Merge tag 'docs-5.13-2' of git://git.lwn.net/linux

[linux-2.6-microblaze.git] / net / ipv4 / udp.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              The User Datagram Protocol (UDP).
 *
 * Authors:     Ross Biro
 *              Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
 *              Arnt Gulbrandsen, <agulbra@nvg.unit.no>
 *              Alan Cox, <alan@lxorguk.ukuu.org.uk>
 *              Hirokazu Takahashi, <taka@valinux.co.jp>
 *
 * Fixes:
 *              Alan Cox        :       verify_area() calls
 *              Alan Cox        :       stopped close while in use off icmp
 *                                      messages. Not a fix but a botch that
 *                                      for udp at least is 'valid'.
 *              Alan Cox        :       Fixed icmp handling properly
 *              Alan Cox        :       Correct error for oversized datagrams
 *              Alan Cox        :       Tidied select() semantics.
 *              Alan Cox        :       udp_err() fixed properly, also now
 *                                      select and read wake correctly on errors
 *              Alan Cox        :       udp_send verify_area moved to avoid mem leak
 *              Alan Cox        :       UDP can count its memory
 *              Alan Cox        :       send to an unknown connection causes
 *                                      an ECONNREFUSED off the icmp, but
 *                                      does NOT close.
 *              Alan Cox        :       Switched to new sk_buff handlers. No more backlog!
 *              Alan Cox        :       Using generic datagram code. Even smaller and the PEEK
 *                                      bug no longer crashes it.
 *              Fred Van Kempen :       Net2e support for sk->broadcast.
 *              Alan Cox        :       Uses skb_free_datagram
 *              Alan Cox        :       Added get/set sockopt support.
 *              Alan Cox        :       Broadcasting without option set returns EACCES.
 *              Alan Cox        :       No wakeup calls. Instead we now use the callbacks.
 *              Alan Cox        :       Use ip_tos and ip_ttl
 *              Alan Cox        :       SNMP Mibs
 *              Alan Cox        :       MSG_DONTROUTE, and 0.0.0.0 support.
 *              Matt Dillon     :       UDP length checks.
 *              Alan Cox        :       Smarter af_inet used properly.
 *              Alan Cox        :       Use new kernel side addressing.
 *              Alan Cox        :       Incorrect return on truncated datagram receive.
 *      Arnt Gulbrandsen        :       New udp_send and stuff
 *              Alan Cox        :       Cache last socket
 *              Alan Cox        :       Route cache
 *              Jon Peatfield   :       Minor efficiency fix to sendto().
 *              Mike Shaver     :       RFC1122 checks.
 *              Alan Cox        :       Nonblocking error fix.
 *      Willy Konynenberg       :       Transparent proxying support.
 *              Mike McLagan    :       Routing by source
 *              David S. Miller :       New socket lookup architecture.
 *                                      Last socket cache retained as it
 *                                      does have a high hit rate.
 *              Olaf Kirch      :       Don't linearise iovec on sendmsg.
 *              Andi Kleen      :       Some cleanups, cache destination entry
 *                                      for connect.
 *      Vitaly E. Lavrov        :       Transparent proxy revived after year coma.
 *              Melvin Smith    :       Check msg_name not msg_namelen in sendto(),
 *                                      return ENOTCONN for unconnected sockets (POSIX)
 *              Janos Farkas    :       don't deliver multi/broadcasts to a different
 *                                      bound-to-device socket
 *      Hirokazu Takahashi      :       HW checksumming for outgoing UDP
 *                                      datagrams.
 *      Hirokazu Takahashi      :       sendfile() on UDP works now.
 *              Arnaldo C. Melo :       convert /proc/net/udp to seq_file
 *      YOSHIFUJI Hideaki @USAGI and:   Support IPV6_V6ONLY socket option, which
 *      Alexey Kuznetsov:               allow both IPv4 and IPv6 sockets to bind
 *                                      a single port at the same time.
 *      Derek Atkins <derek@ihtfp.com>: Add Encapulation Support
 *      James Chapman           :       Add L2TP encapsulation type.
 */

#define pr_fmt(fmt) "UDP: " fmt

#include <linux/uaccess.h>
#include <asm/ioctls.h>
#include <linux/memblock.h>
#include <linux/highmem.h>
#include <linux/swap.h>
#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/module.h>
#include <linux/socket.h>
#include <linux/sockios.h>
#include <linux/igmp.h>
#include <linux/inetdevice.h>
#include <linux/in.h>
#include <linux/errno.h>
#include <linux/timer.h>
#include <linux/mm.h>
#include <linux/inet.h>
#include <linux/netdevice.h>
#include <linux/slab.h>
#include <net/tcp_states.h>
#include <linux/skbuff.h>
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
#include <net/net_namespace.h>
#include <net/icmp.h>
#include <net/inet_hashtables.h>
#include <net/ip_tunnels.h>
#include <net/route.h>
#include <net/checksum.h>
#include <net/xfrm.h>
#include <trace/events/udp.h>
#include <linux/static_key.h>
#include <linux/btf_ids.h>
#include <trace/events/skb.h>
#include <net/busy_poll.h>
#include "udp_impl.h"
#include <net/sock_reuseport.h>
#include <net/addrconf.h>
#include <net/udp_tunnel.h>
#if IS_ENABLED(CONFIG_IPV6)
#include <net/ipv6_stubs.h>
#endif

struct udp_table udp_table __read_mostly;
EXPORT_SYMBOL(udp_table);

long sysctl_udp_mem[3] __read_mostly;
EXPORT_SYMBOL(sysctl_udp_mem);

atomic_long_t udp_memory_allocated;
EXPORT_SYMBOL(udp_memory_allocated);

#define MAX_UDP_PORTS 65536
#define PORTS_PER_CHAIN (MAX_UDP_PORTS / UDP_HTABLE_SIZE_MIN)

static int udp_lib_lport_inuse(struct net *net, __u16 num,
                               const struct udp_hslot *hslot,
                               unsigned long *bitmap,
                               struct sock *sk, unsigned int log)
{
        struct sock *sk2;
        kuid_t uid = sock_i_uid(sk);

        sk_for_each(sk2, &hslot->head) {
                if (net_eq(sock_net(sk2), net) &&
                    sk2 != sk &&
                    (bitmap || udp_sk(sk2)->udp_port_hash == num) &&
                    (!sk2->sk_reuse || !sk->sk_reuse) &&
                    (!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if ||
                     sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
                    inet_rcv_saddr_equal(sk, sk2, true)) {
                        if (sk2->sk_reuseport && sk->sk_reuseport &&
                            !rcu_access_pointer(sk->sk_reuseport_cb) &&
                            uid_eq(uid, sock_i_uid(sk2))) {
                                if (!bitmap)
                                        return 0;
                        } else {
                                if (!bitmap)
                                        return 1;
                                __set_bit(udp_sk(sk2)->udp_port_hash >> log,
                                          bitmap);
                        }
                }
        }
        return 0;
}

/*
 * Note: we still hold spinlock of primary hash chain, so no other writer
 * can insert/delete a socket with local_port == num
 */
static int udp_lib_lport_inuse2(struct net *net, __u16 num,
                                struct udp_hslot *hslot2,
                                struct sock *sk)
{
        struct sock *sk2;
        kuid_t uid = sock_i_uid(sk);
        int res = 0;

        spin_lock(&hslot2->lock);
        udp_portaddr_for_each_entry(sk2, &hslot2->head) {
                if (net_eq(sock_net(sk2), net) &&
                    sk2 != sk &&
                    (udp_sk(sk2)->udp_port_hash == num) &&
                    (!sk2->sk_reuse || !sk->sk_reuse) &&
                    (!sk2->sk_bound_dev_if || !sk->sk_bound_dev_if ||
                     sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
                    inet_rcv_saddr_equal(sk, sk2, true)) {
                        if (sk2->sk_reuseport && sk->sk_reuseport &&
                            !rcu_access_pointer(sk->sk_reuseport_cb) &&
                            uid_eq(uid, sock_i_uid(sk2))) {
                                res = 0;
                        } else {
                                res = 1;
                        }
                        break;
                }
        }
        spin_unlock(&hslot2->lock);
        return res;
}

static int udp_reuseport_add_sock(struct sock *sk, struct udp_hslot *hslot)
{
        struct net *net = sock_net(sk);
        kuid_t uid = sock_i_uid(sk);
        struct sock *sk2;

        sk_for_each(sk2, &hslot->head) {
                if (net_eq(sock_net(sk2), net) &&
                    sk2 != sk &&
                    sk2->sk_family == sk->sk_family &&
                    ipv6_only_sock(sk2) == ipv6_only_sock(sk) &&
                    (udp_sk(sk2)->udp_port_hash == udp_sk(sk)->udp_port_hash) &&
                    (sk2->sk_bound_dev_if == sk->sk_bound_dev_if) &&
                    sk2->sk_reuseport && uid_eq(uid, sock_i_uid(sk2)) &&
                    inet_rcv_saddr_equal(sk, sk2, false)) {
                        return reuseport_add_sock(sk, sk2,
                                                  inet_rcv_saddr_any(sk));
                }
        }

        return reuseport_alloc(sk, inet_rcv_saddr_any(sk));
}

/**
 *  udp_lib_get_port  -  UDP/-Lite port lookup for IPv4 and IPv6
 *
 *  @sk:          socket struct in question
 *  @snum:        port number to look up
 *  @hash2_nulladdr: AF-dependent hash value in secondary hash chains,
 *                   with NULL address
 */
int udp_lib_get_port(struct sock *sk, unsigned short snum,
                     unsigned int hash2_nulladdr)
{
        struct udp_hslot *hslot, *hslot2;
        struct udp_table *udptable = sk->sk_prot->h.udp_table;
        int    error = 1;
        struct net *net = sock_net(sk);

        if (!snum) {
                int low, high, remaining;
                unsigned int rand;
                unsigned short first, last;
                DECLARE_BITMAP(bitmap, PORTS_PER_CHAIN);

                inet_get_local_port_range(net, &low, &high);
                remaining = (high - low) + 1;

                rand = prandom_u32();
                first = reciprocal_scale(rand, remaining) + low;
                /*
                 * force rand to be an odd multiple of UDP_HTABLE_SIZE
                 */
                rand = (rand | 1) * (udptable->mask + 1);
                last = first + udptable->mask + 1;
                do {
                        hslot = udp_hashslot(udptable, net, first);
                        bitmap_zero(bitmap, PORTS_PER_CHAIN);
                        spin_lock_bh(&hslot->lock);
                        udp_lib_lport_inuse(net, snum, hslot, bitmap, sk,
                                            udptable->log);

                        snum = first;
                        /*
                         * Iterate on all possible values of snum for this hash.
                         * Using steps of an odd multiple of UDP_HTABLE_SIZE
                         * give us randomization and full range coverage.
                         */
                        do {
                                if (low <= snum && snum <= high &&
                                    !test_bit(snum >> udptable->log, bitmap) &&
                                    !inet_is_local_reserved_port(net, snum))
                                        goto found;
                                snum += rand;
                        } while (snum != first);
                        spin_unlock_bh(&hslot->lock);
                        cond_resched();
                } while (++first != last);
                goto fail;
        } else {
                hslot = udp_hashslot(udptable, net, snum);
                spin_lock_bh(&hslot->lock);
                if (hslot->count > 10) {
                        int exist;
                        unsigned int slot2 = udp_sk(sk)->udp_portaddr_hash ^ snum;

                        slot2          &= udptable->mask;
                        hash2_nulladdr &= udptable->mask;

                        hslot2 = udp_hashslot2(udptable, slot2);
                        if (hslot->count < hslot2->count)
                                goto scan_primary_hash;

                        exist = udp_lib_lport_inuse2(net, snum, hslot2, sk);
                        if (!exist && (hash2_nulladdr != slot2)) {
                                hslot2 = udp_hashslot2(udptable, hash2_nulladdr);
                                exist = udp_lib_lport_inuse2(net, snum, hslot2,
                                                             sk);
                        }
                        if (exist)
                                goto fail_unlock;
                        else
                                goto found;
                }
scan_primary_hash:
                if (udp_lib_lport_inuse(net, snum, hslot, NULL, sk, 0))
                        goto fail_unlock;
        }
found:
        inet_sk(sk)->inet_num = snum;
        udp_sk(sk)->udp_port_hash = snum;
        udp_sk(sk)->udp_portaddr_hash ^= snum;
        if (sk_unhashed(sk)) {
                if (sk->sk_reuseport &&
                    udp_reuseport_add_sock(sk, hslot)) {
                        inet_sk(sk)->inet_num = 0;
                        udp_sk(sk)->udp_port_hash = 0;
                        udp_sk(sk)->udp_portaddr_hash ^= snum;
                        goto fail_unlock;
                }

                sk_add_node_rcu(sk, &hslot->head);
                hslot->count++;
                sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);

                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);
                spin_lock(&hslot2->lock);
                if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport &&
                    sk->sk_family == AF_INET6)
                        hlist_add_tail_rcu(&udp_sk(sk)->udp_portaddr_node,
                                           &hslot2->head);
                else
                        hlist_add_head_rcu(&udp_sk(sk)->udp_portaddr_node,
                                           &hslot2->head);
                hslot2->count++;
                spin_unlock(&hslot2->lock);
        }
        sock_set_flag(sk, SOCK_RCU_FREE);
        error = 0;
fail_unlock:
        spin_unlock_bh(&hslot->lock);
fail:
        return error;
}
EXPORT_SYMBOL(udp_lib_get_port);

int udp_v4_get_port(struct sock *sk, unsigned short snum)
{
        unsigned int hash2_nulladdr =
                ipv4_portaddr_hash(sock_net(sk), htonl(INADDR_ANY), snum);
        unsigned int hash2_partial =
                ipv4_portaddr_hash(sock_net(sk), inet_sk(sk)->inet_rcv_saddr, 0);

        /* precompute partial secondary hash */
        udp_sk(sk)->udp_portaddr_hash = hash2_partial;
        return udp_lib_get_port(sk, snum, hash2_nulladdr);
}

static int compute_score(struct sock *sk, struct net *net,
                         __be32 saddr, __be16 sport,
                         __be32 daddr, unsigned short hnum,
                         int dif, int sdif)
{
        int score;
        struct inet_sock *inet;
        bool dev_match;

        if (!net_eq(sock_net(sk), net) ||
            udp_sk(sk)->udp_port_hash != hnum ||
            ipv6_only_sock(sk))
                return -1;

        if (sk->sk_rcv_saddr != daddr)
                return -1;

        score = (sk->sk_family == PF_INET) ? 2 : 1;

        inet = inet_sk(sk);
        if (inet->inet_daddr) {
                if (inet->inet_daddr != saddr)
                        return -1;
                score += 4;
        }

        if (inet->inet_dport) {
                if (inet->inet_dport != sport)
                        return -1;
                score += 4;
        }

        dev_match = udp_sk_bound_dev_eq(net, sk->sk_bound_dev_if,
                                        dif, sdif);
        if (!dev_match)
                return -1;
        score += 4;

        if (READ_ONCE(sk->sk_incoming_cpu) == raw_smp_processor_id())
                score++;
        return score;
}

static u32 udp_ehashfn(const struct net *net, const __be32 laddr,
                       const __u16 lport, const __be32 faddr,
                       const __be16 fport)
{
        static u32 udp_ehash_secret __read_mostly;

        net_get_random_once(&udp_ehash_secret, sizeof(udp_ehash_secret));

        return __inet_ehashfn(laddr, lport, faddr, fport,
                              udp_ehash_secret + net_hash_mix(net));
}

static struct sock *lookup_reuseport(struct net *net, struct sock *sk,
                                     struct sk_buff *skb,
                                     __be32 saddr, __be16 sport,
                                     __be32 daddr, unsigned short hnum)
{
        struct sock *reuse_sk = NULL;
        u32 hash;

        if (sk->sk_reuseport && sk->sk_state != TCP_ESTABLISHED) {
                hash = udp_ehashfn(net, daddr, hnum, saddr, sport);
                reuse_sk = reuseport_select_sock(sk, hash, skb,
                                                 sizeof(struct udphdr));
        }
        return reuse_sk;
}

/* called with rcu_read_lock() */
static struct sock *udp4_lib_lookup2(struct net *net,
                                     __be32 saddr, __be16 sport,
                                     __be32 daddr, unsigned int hnum,
                                     int dif, int sdif,
                                     struct udp_hslot *hslot2,
                                     struct sk_buff *skb)
{
        struct sock *sk, *result;
        int score, badness;

        result = NULL;
        badness = 0;
        udp_portaddr_for_each_entry_rcu(sk, &hslot2->head) {
                score = compute_score(sk, net, saddr, sport,
                                      daddr, hnum, dif, sdif);
                if (score > badness) {
                        result = lookup_reuseport(net, sk, skb,
                                                  saddr, sport, daddr, hnum);
                        /* Fall back to scoring if group has connections */
                        if (result && !reuseport_has_conns(sk, false))
                                return result;

                        result = result ? : sk;
                        badness = score;
                }
        }
        return result;
}

static struct sock *udp4_lookup_run_bpf(struct net *net,
                                        struct udp_table *udptable,
                                        struct sk_buff *skb,
                                        __be32 saddr, __be16 sport,
                                        __be32 daddr, u16 hnum)
{
        struct sock *sk, *reuse_sk;
        bool no_reuseport;

        if (udptable != &udp_table)
                return NULL; /* only UDP is supported */

        no_reuseport = bpf_sk_lookup_run_v4(net, IPPROTO_UDP,
                                            saddr, sport, daddr, hnum, &sk);
        if (no_reuseport || IS_ERR_OR_NULL(sk))
                return sk;

        reuse_sk = lookup_reuseport(net, sk, skb, saddr, sport, daddr, hnum);
        if (reuse_sk)
                sk = reuse_sk;
        return sk;
}

/* UDP is nearly always wildcards out the wazoo, it makes no sense to try
 * harder than this. -DaveM
 */
struct sock *__udp4_lib_lookup(struct net *net, __be32 saddr,
                __be16 sport, __be32 daddr, __be16 dport, int dif,
                int sdif, struct udp_table *udptable, struct sk_buff *skb)
{
        unsigned short hnum = ntohs(dport);
        unsigned int hash2, slot2;
        struct udp_hslot *hslot2;
        struct sock *result, *sk;

        hash2 = ipv4_portaddr_hash(net, daddr, hnum);
        slot2 = hash2 & udptable->mask;
        hslot2 = &udptable->hash2[slot2];

        /* Lookup connected or non-wildcard socket */
        result = udp4_lib_lookup2(net, saddr, sport,
                                  daddr, hnum, dif, sdif,
                                  hslot2, skb);
        if (!IS_ERR_OR_NULL(result) && result->sk_state == TCP_ESTABLISHED)
                goto done;

        /* Lookup redirect from BPF */
        if (static_branch_unlikely(&bpf_sk_lookup_enabled)) {
                sk = udp4_lookup_run_bpf(net, udptable, skb,
                                         saddr, sport, daddr, hnum);
                if (sk) {
                        result = sk;
                        goto done;
                }
        }

        /* Got non-wildcard socket or error on first lookup */
        if (result)
                goto done;

        /* Lookup wildcard sockets */
        hash2 = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum);
        slot2 = hash2 & udptable->mask;
        hslot2 = &udptable->hash2[slot2];

        result = udp4_lib_lookup2(net, saddr, sport,
                                  htonl(INADDR_ANY), hnum, dif, sdif,
                                  hslot2, skb);
done:
        if (IS_ERR(result))
                return NULL;
        return result;
}
EXPORT_SYMBOL_GPL(__udp4_lib_lookup);

static inline struct sock *__udp4_lib_lookup_skb(struct sk_buff *skb,
                                                 __be16 sport, __be16 dport,
                                                 struct udp_table *udptable)
{
        const struct iphdr *iph = ip_hdr(skb);

        return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
                                 iph->daddr, dport, inet_iif(skb),
                                 inet_sdif(skb), udptable, skb);
}

struct sock *udp4_lib_lookup_skb(const struct sk_buff *skb,
                                 __be16 sport, __be16 dport)
{
        const struct iphdr *iph = ip_hdr(skb);

        return __udp4_lib_lookup(dev_net(skb->dev), iph->saddr, sport,
                                 iph->daddr, dport, inet_iif(skb),
                                 inet_sdif(skb), &udp_table, NULL);
}

/* Must be called under rcu_read_lock().
 * Does increment socket refcount.
 */
#if IS_ENABLED(CONFIG_NF_TPROXY_IPV4) || IS_ENABLED(CONFIG_NF_SOCKET_IPV4)
struct sock *udp4_lib_lookup(struct net *net, __be32 saddr, __be16 sport,
                             __be32 daddr, __be16 dport, int dif)
{
        struct sock *sk;

        sk = __udp4_lib_lookup(net, saddr, sport, daddr, dport,
                               dif, 0, &udp_table, NULL);
        if (sk && !refcount_inc_not_zero(&sk->sk_refcnt))
                sk = NULL;
        return sk;
}
EXPORT_SYMBOL_GPL(udp4_lib_lookup);
#endif

static inline bool __udp_is_mcast_sock(struct net *net, struct sock *sk,
                                       __be16 loc_port, __be32 loc_addr,
                                       __be16 rmt_port, __be32 rmt_addr,
                                       int dif, int sdif, unsigned short hnum)
{
        struct inet_sock *inet = inet_sk(sk);

        if (!net_eq(sock_net(sk), net) ||
            udp_sk(sk)->udp_port_hash != hnum ||
            (inet->inet_daddr && inet->inet_daddr != rmt_addr) ||
            (inet->inet_dport != rmt_port && inet->inet_dport) ||
            (inet->inet_rcv_saddr && inet->inet_rcv_saddr != loc_addr) ||
            ipv6_only_sock(sk) ||
            !udp_sk_bound_dev_eq(net, sk->sk_bound_dev_if, dif, sdif))
                return false;
        if (!ip_mc_sf_allow(sk, loc_addr, rmt_addr, dif, sdif))
                return false;
        return true;
}

DEFINE_STATIC_KEY_FALSE(udp_encap_needed_key);
void udp_encap_enable(void)
{
        static_branch_inc(&udp_encap_needed_key);
}
EXPORT_SYMBOL(udp_encap_enable);

void udp_encap_disable(void)
{
        static_branch_dec(&udp_encap_needed_key);
}
EXPORT_SYMBOL(udp_encap_disable);

/* Handler for tunnels with arbitrary destination ports: no socket lookup, go
 * through error handlers in encapsulations looking for a match.
 */
static int __udp4_lib_err_encap_no_sk(struct sk_buff *skb, u32 info)
{
        int i;

        for (i = 0; i < MAX_IPTUN_ENCAP_OPS; i++) {
                int (*handler)(struct sk_buff *skb, u32 info);
                const struct ip_tunnel_encap_ops *encap;

                encap = rcu_dereference(iptun_encaps[i]);
                if (!encap)
                        continue;
                handler = encap->err_handler;
                if (handler && !handler(skb, info))
                        return 0;
        }

        return -ENOENT;
}

/* Try to match ICMP errors to UDP tunnels by looking up a socket without
 * reversing source and destination port: this will match tunnels that force the
 * same destination port on both endpoints (e.g. VXLAN, GENEVE). Note that
 * lwtunnels might actually break this assumption by being configured with
 * different destination ports on endpoints, in this case we won't be able to
 * trace ICMP messages back to them.
 *
 * If this doesn't match any socket, probe tunnels with arbitrary destination
 * ports (e.g. FoU, GUE): there, the receiving socket is useless, as the port
 * we've sent packets to won't necessarily match the local destination port.
 *
 * Then ask the tunnel implementation to match the error against a valid
 * association.
 *
 * Return an error if we can't find a match, the socket if we need further
 * processing, zero otherwise.
 */
static struct sock *__udp4_lib_err_encap(struct net *net,
                                         const struct iphdr *iph,
                                         struct udphdr *uh,
                                         struct udp_table *udptable,
                                         struct sk_buff *skb, u32 info)
{
        int network_offset, transport_offset;
        struct sock *sk;

        network_offset = skb_network_offset(skb);
        transport_offset = skb_transport_offset(skb);

        /* Network header needs to point to the outer IPv4 header inside ICMP */
        skb_reset_network_header(skb);

        /* Transport header needs to point to the UDP header */
        skb_set_transport_header(skb, iph->ihl << 2);

        sk = __udp4_lib_lookup(net, iph->daddr, uh->source,
                               iph->saddr, uh->dest, skb->dev->ifindex, 0,
                               udptable, NULL);
        if (sk) {
                int (*lookup)(struct sock *sk, struct sk_buff *skb);
                struct udp_sock *up = udp_sk(sk);

                lookup = READ_ONCE(up->encap_err_lookup);
                if (!lookup || lookup(sk, skb))
                        sk = NULL;
        }

        if (!sk)
                sk = ERR_PTR(__udp4_lib_err_encap_no_sk(skb, info));

        skb_set_transport_header(skb, transport_offset);
        skb_set_network_header(skb, network_offset);

        return sk;
}

/*
 * This routine is called by the ICMP module when it gets some
 * sort of error condition.  If err < 0 then the socket should
 * be closed and the error returned to the user.  If err > 0
 * it's just the icmp type << 8 | icmp code.
 * Header points to the ip header of the error packet. We move
 * on past this. Then (as it used to claim before adjustment)
 * header points to the first 8 bytes of the udp header.  We need
 * to find the appropriate port.
 */

int __udp4_lib_err(struct sk_buff *skb, u32 info, struct udp_table *udptable)
{
        struct inet_sock *inet;
        const struct iphdr *iph = (const struct iphdr *)skb->data;
        struct udphdr *uh = (struct udphdr *)(skb->data+(iph->ihl<<2));
        const int type = icmp_hdr(skb)->type;
        const int code = icmp_hdr(skb)->code;
        bool tunnel = false;
        struct sock *sk;
        int harderr;
        int err;
        struct net *net = dev_net(skb->dev);

        sk = __udp4_lib_lookup(net, iph->daddr, uh->dest,
                               iph->saddr, uh->source, skb->dev->ifindex,
                               inet_sdif(skb), udptable, NULL);
        if (!sk || udp_sk(sk)->encap_type) {
                /* No socket for error: try tunnels before discarding */
                sk = ERR_PTR(-ENOENT);
                if (static_branch_unlikely(&udp_encap_needed_key)) {
                        sk = __udp4_lib_err_encap(net, iph, uh, udptable, skb,
                                                  info);
                        if (!sk)
                                return 0;
                }

                if (IS_ERR(sk)) {
                        __ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
                        return PTR_ERR(sk);
                }

                tunnel = true;
        }

        err = 0;
        harderr = 0;
        inet = inet_sk(sk);

        switch (type) {
        default:
        case ICMP_TIME_EXCEEDED:
                err = EHOSTUNREACH;
                break;
        case ICMP_SOURCE_QUENCH:
                goto out;
        case ICMP_PARAMETERPROB:
                err = EPROTO;
                harderr = 1;
                break;
        case ICMP_DEST_UNREACH:
                if (code == ICMP_FRAG_NEEDED) { /* Path MTU discovery */
                        ipv4_sk_update_pmtu(skb, sk, info);
                        if (inet->pmtudisc != IP_PMTUDISC_DONT) {
                                err = EMSGSIZE;
                                harderr = 1;
                                break;
                        }
                        goto out;
                }
                err = EHOSTUNREACH;
                if (code <= NR_ICMP_UNREACH) {
                        harderr = icmp_err_convert[code].fatal;
                        err = icmp_err_convert[code].errno;
                }
                break;
        case ICMP_REDIRECT:
                ipv4_sk_redirect(skb, sk);
                goto out;
        }

        /*
         *      RFC1122: OK.  Passes ICMP errors back to application, as per
         *      4.1.3.3.
         */
        if (tunnel) {
                /* ...not for tunnels though: we don't have a sending socket */
                goto out;
        }
        if (!inet->recverr) {
                if (!harderr || sk->sk_state != TCP_ESTABLISHED)
                        goto out;
        } else
                ip_icmp_error(sk, skb, err, uh->dest, info, (u8 *)(uh+1));

        sk->sk_err = err;
        sk->sk_error_report(sk);
out:
        return 0;
}

int udp_err(struct sk_buff *skb, u32 info)
{
        return __udp4_lib_err(skb, info, &udp_table);
}

/*
 * Throw away all pending data and cancel the corking. Socket is locked.
 */
void udp_flush_pending_frames(struct sock *sk)
{
        struct udp_sock *up = udp_sk(sk);

        if (up->pending) {
                up->len = 0;
                up->pending = 0;
                ip_flush_pending_frames(sk);
        }
}
EXPORT_SYMBOL(udp_flush_pending_frames);

/**
 *      udp4_hwcsum  -  handle outgoing HW checksumming
 *      @skb:   sk_buff containing the filled-in UDP header
 *              (checksum field must be zeroed out)
 *      @src:   source IP address
 *      @dst:   destination IP address
 */
void udp4_hwcsum(struct sk_buff *skb, __be32 src, __be32 dst)
{
        struct udphdr *uh = udp_hdr(skb);
        int offset = skb_transport_offset(skb);
        int len = skb->len - offset;
        int hlen = len;
        __wsum csum = 0;

        if (!skb_has_frag_list(skb)) {
                /*
                 * Only one fragment on the socket.
                 */
                skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct udphdr, check);
                uh->check = ~csum_tcpudp_magic(src, dst, len,
                                               IPPROTO_UDP, 0);
        } else {
                struct sk_buff *frags;

                /*
                 * HW-checksum won't work as there are two or more
                 * fragments on the socket so that all csums of sk_buffs
                 * should be together
                 */
                skb_walk_frags(skb, frags) {
                        csum = csum_add(csum, frags->csum);
                        hlen -= frags->len;
                }

                csum = skb_checksum(skb, offset, hlen, csum);
                skb->ip_summed = CHECKSUM_NONE;

                uh->check = csum_tcpudp_magic(src, dst, len, IPPROTO_UDP, csum);
                if (uh->check == 0)
                        uh->check = CSUM_MANGLED_0;
        }
}
EXPORT_SYMBOL_GPL(udp4_hwcsum);

/* Function to set UDP checksum for an IPv4 UDP packet. This is intended
 * for the simple case like when setting the checksum for a UDP tunnel.
 */
void udp_set_csum(bool nocheck, struct sk_buff *skb,
                  __be32 saddr, __be32 daddr, int len)
{
        struct udphdr *uh = udp_hdr(skb);

        if (nocheck) {
                uh->check = 0;
        } else if (skb_is_gso(skb)) {
                uh->check = ~udp_v4_check(len, saddr, daddr, 0);
        } else if (skb->ip_summed == CHECKSUM_PARTIAL) {
                uh->check = 0;
                uh->check = udp_v4_check(len, saddr, daddr, lco_csum(skb));
                if (uh->check == 0)
                        uh->check = CSUM_MANGLED_0;
        } else {
                skb->ip_summed = CHECKSUM_PARTIAL;
                skb->csum_start = skb_transport_header(skb) - skb->head;
                skb->csum_offset = offsetof(struct udphdr, check);
                uh->check = ~udp_v4_check(len, saddr, daddr, 0);
        }
}
EXPORT_SYMBOL(udp_set_csum);

static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
                        struct inet_cork *cork)
{
        struct sock *sk = skb->sk;
        struct inet_sock *inet = inet_sk(sk);
        struct udphdr *uh;
        int err;
        int is_udplite = IS_UDPLITE(sk);
        int offset = skb_transport_offset(skb);
        int len = skb->len - offset;
        int datalen = len - sizeof(*uh);
        __wsum csum = 0;

        /*
         * Create a UDP header
         */
        uh = udp_hdr(skb);
        uh->source = inet->inet_sport;
        uh->dest = fl4->fl4_dport;
        uh->len = htons(len);
        uh->check = 0;

        if (cork->gso_size) {
                const int hlen = skb_network_header_len(skb) +
                                 sizeof(struct udphdr);

                if (hlen + cork->gso_size > cork->fragsize) {
                        kfree_skb(skb);
                        return -EINVAL;
                }
                if (skb->len > cork->gso_size * UDP_MAX_SEGMENTS) {
                        kfree_skb(skb);
                        return -EINVAL;
                }
                if (sk->sk_no_check_tx) {
                        kfree_skb(skb);
                        return -EINVAL;
                }
                if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
                    dst_xfrm(skb_dst(skb))) {
                        kfree_skb(skb);
                        return -EIO;
                }

                if (datalen > cork->gso_size) {
                        skb_shinfo(skb)->gso_size = cork->gso_size;
                        skb_shinfo(skb)->gso_type = SKB_GSO_UDP_L4;
                        skb_shinfo(skb)->gso_segs = DIV_ROUND_UP(datalen,
                                                                 cork->gso_size);
                }
                goto csum_partial;
        }

        if (is_udplite)                                  /*     UDP-Lite      */
                csum = udplite_csum(skb);

        else if (sk->sk_no_check_tx) {                   /* UDP csum off */

                skb->ip_summed = CHECKSUM_NONE;
                goto send;

        } else if (skb->ip_summed == CHECKSUM_PARTIAL) { /* UDP hardware csum */
csum_partial:

                udp4_hwcsum(skb, fl4->saddr, fl4->daddr);
                goto send;

        } else
                csum = udp_csum(skb);

        /* add protocol-dependent pseudo-header */
        uh->check = csum_tcpudp_magic(fl4->saddr, fl4->daddr, len,
                                      sk->sk_protocol, csum);
        if (uh->check == 0)
                uh->check = CSUM_MANGLED_0;

send:
        err = ip_send_skb(sock_net(sk), skb);
        if (err) {
                if (err == -ENOBUFS && !inet->recverr) {
                        UDP_INC_STATS(sock_net(sk),
                                      UDP_MIB_SNDBUFERRORS, is_udplite);
                        err = 0;
                }
        } else
                UDP_INC_STATS(sock_net(sk),
                              UDP_MIB_OUTDATAGRAMS, is_udplite);
        return err;
}

/*
 * Push out all pending data as one UDP datagram. Socket is locked.
 */
int udp_push_pending_frames(struct sock *sk)
{
        struct udp_sock  *up = udp_sk(sk);
        struct inet_sock *inet = inet_sk(sk);
        struct flowi4 *fl4 = &inet->cork.fl.u.ip4;
        struct sk_buff *skb;
        int err = 0;

        skb = ip_finish_skb(sk, fl4);
        if (!skb)
                goto out;

        err = udp_send_skb(skb, fl4, &inet->cork.base);

out:
        up->len = 0;
        up->pending = 0;
        return err;
}
EXPORT_SYMBOL(udp_push_pending_frames);

static int __udp_cmsg_send(struct cmsghdr *cmsg, u16 *gso_size)
{
        switch (cmsg->cmsg_type) {
        case UDP_SEGMENT:
                if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u16)))
                        return -EINVAL;
                *gso_size = *(__u16 *)CMSG_DATA(cmsg);
                return 0;
        default:
                return -EINVAL;
        }
}

int udp_cmsg_send(struct sock *sk, struct msghdr *msg, u16 *gso_size)
{
        struct cmsghdr *cmsg;
        bool need_ip = false;
        int err;

        for_each_cmsghdr(cmsg, msg) {
                if (!CMSG_OK(msg, cmsg))
                        return -EINVAL;

                if (cmsg->cmsg_level != SOL_UDP) {
                        need_ip = true;
                        continue;
                }

                err = __udp_cmsg_send(cmsg, gso_size);
                if (err)
                        return err;
        }

        return need_ip;
}
EXPORT_SYMBOL_GPL(udp_cmsg_send);

int udp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
{
        struct inet_sock *inet = inet_sk(sk);
        struct udp_sock *up = udp_sk(sk);
        DECLARE_SOCKADDR(struct sockaddr_in *, usin, msg->msg_name);
        struct flowi4 fl4_stack;
        struct flowi4 *fl4;
        int ulen = len;
        struct ipcm_cookie ipc;
        struct rtable *rt = NULL;
        int free = 0;
        int connected = 0;
        __be32 daddr, faddr, saddr;
        __be16 dport;
        u8  tos;
        int err, is_udplite = IS_UDPLITE(sk);
        int corkreq = up->corkflag || msg->msg_flags&MSG_MORE;
        int (*getfrag)(void *, char *, int, int, int, struct sk_buff *);
        struct sk_buff *skb;
        struct ip_options_data opt_copy;

        if (len > 0xFFFF)
                return -EMSGSIZE;

        /*
         *      Check the flags.
         */

        if (msg->msg_flags & MSG_OOB) /* Mirror BSD error message compatibility */
                return -EOPNOTSUPP;

        getfrag = is_udplite ? udplite_getfrag : ip_generic_getfrag;

        fl4 = &inet->cork.fl.u.ip4;
        if (up->pending) {
                /*
                 * There are pending frames.
                 * The socket lock must be held while it's corked.
                 */
                lock_sock(sk);
                if (likely(up->pending)) {
                        if (unlikely(up->pending != AF_INET)) {
                                release_sock(sk);
                                return -EINVAL;
                        }
                        goto do_append_data;
                }
                release_sock(sk);
        }
        ulen += sizeof(struct udphdr);

        /*
         *      Get and verify the address.
         */
        if (usin) {
                if (msg->msg_namelen < sizeof(*usin))
                        return -EINVAL;
                if (usin->sin_family != AF_INET) {
                        if (usin->sin_family != AF_UNSPEC)
                                return -EAFNOSUPPORT;
                }

                daddr = usin->sin_addr.s_addr;
                dport = usin->sin_port;
                if (dport == 0)
                        return -EINVAL;
        } else {
                if (sk->sk_state != TCP_ESTABLISHED)
                        return -EDESTADDRREQ;
                daddr = inet->inet_daddr;
                dport = inet->inet_dport;
                /* Open fast path for connected socket.
                   Route will not be used, if at least one option is set.
                 */
                connected = 1;
        }

        ipcm_init_sk(&ipc, inet);
        ipc.gso_size = up->gso_size;

        if (msg->msg_controllen) {
                err = udp_cmsg_send(sk, msg, &ipc.gso_size);
                if (err > 0)
                        err = ip_cmsg_send(sk, msg, &ipc,
                                           sk->sk_family == AF_INET6);
                if (unlikely(err < 0)) {
                        kfree(ipc.opt);
                        return err;
                }
                if (ipc.opt)
                        free = 1;
                connected = 0;
        }
        if (!ipc.opt) {
                struct ip_options_rcu *inet_opt;

                rcu_read_lock();
                inet_opt = rcu_dereference(inet->inet_opt);
                if (inet_opt) {
                        memcpy(&opt_copy, inet_opt,
                               sizeof(*inet_opt) + inet_opt->opt.optlen);
                        ipc.opt = &opt_copy.opt;
                }
                rcu_read_unlock();
        }

        if (cgroup_bpf_enabled(BPF_CGROUP_UDP4_SENDMSG) && !connected) {
                err = BPF_CGROUP_RUN_PROG_UDP4_SENDMSG_LOCK(sk,
                                            (struct sockaddr *)usin, &ipc.addr);
                if (err)
                        goto out_free;
                if (usin) {
                        if (usin->sin_port == 0) {
                                /* BPF program set invalid port. Reject it. */
                                err = -EINVAL;
                                goto out_free;
                        }
                        daddr = usin->sin_addr.s_addr;
                        dport = usin->sin_port;
                }
        }

        saddr = ipc.addr;
        ipc.addr = faddr = daddr;

        if (ipc.opt && ipc.opt->opt.srr) {
                if (!daddr) {
                        err = -EINVAL;
                        goto out_free;
                }
                faddr = ipc.opt->opt.faddr;
                connected = 0;
        }
        tos = get_rttos(&ipc, inet);
        if (sock_flag(sk, SOCK_LOCALROUTE) ||
            (msg->msg_flags & MSG_DONTROUTE) ||
            (ipc.opt && ipc.opt->opt.is_strictroute)) {
                tos |= RTO_ONLINK;
                connected = 0;
        }

        if (ipv4_is_multicast(daddr)) {
                if (!ipc.oif || netif_index_is_l3_master(sock_net(sk), ipc.oif))
                        ipc.oif = inet->mc_index;
                if (!saddr)
                        saddr = inet->mc_addr;
                connected = 0;
        } else if (!ipc.oif) {
                ipc.oif = inet->uc_index;
        } else if (ipv4_is_lbcast(daddr) && inet->uc_index) {
                /* oif is set, packet is to local broadcast and
                 * uc_index is set. oif is most likely set
                 * by sk_bound_dev_if. If uc_index != oif check if the
                 * oif is an L3 master and uc_index is an L3 slave.
                 * If so, we want to allow the send using the uc_index.
                 */
                if (ipc.oif != inet->uc_index &&
                    ipc.oif == l3mdev_master_ifindex_by_index(sock_net(sk),
                                                              inet->uc_index)) {
                        ipc.oif = inet->uc_index;
                }
        }

        if (connected)
                rt = (struct rtable *)sk_dst_check(sk, 0);

        if (!rt) {
                struct net *net = sock_net(sk);
                __u8 flow_flags = inet_sk_flowi_flags(sk);

                fl4 = &fl4_stack;

                flowi4_init_output(fl4, ipc.oif, ipc.sockc.mark, tos,
                                   RT_SCOPE_UNIVERSE, sk->sk_protocol,
                                   flow_flags,
                                   faddr, saddr, dport, inet->inet_sport,
                                   sk->sk_uid);

                security_sk_classify_flow(sk, flowi4_to_flowi_common(fl4));
                rt = ip_route_output_flow(net, fl4, sk);
                if (IS_ERR(rt)) {
                        err = PTR_ERR(rt);
                        rt = NULL;
                        if (err == -ENETUNREACH)
                                IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
                        goto out;
                }

                err = -EACCES;
                if ((rt->rt_flags & RTCF_BROADCAST) &&
                    !sock_flag(sk, SOCK_BROADCAST))
                        goto out;
                if (connected)
                        sk_dst_set(sk, dst_clone(&rt->dst));
        }

        if (msg->msg_flags&MSG_CONFIRM)
                goto do_confirm;
back_from_confirm:

        saddr = fl4->saddr;
        if (!ipc.addr)
                daddr = ipc.addr = fl4->daddr;

        /* Lockless fast path for the non-corking case. */
        if (!corkreq) {
                struct inet_cork cork;

                skb = ip_make_skb(sk, fl4, getfrag, msg, ulen,
                                  sizeof(struct udphdr), &ipc, &rt,
                                  &cork, msg->msg_flags);
                err = PTR_ERR(skb);
                if (!IS_ERR_OR_NULL(skb))
                        err = udp_send_skb(skb, fl4, &cork);
                goto out;
        }

        lock_sock(sk);
        if (unlikely(up->pending)) {
                /* The socket is already corked while preparing it. */
                /* ... which is an evident application bug. --ANK */
                release_sock(sk);

                net_dbg_ratelimited("socket already corked\n");
                err = -EINVAL;
                goto out;
        }
        /*
         *      Now cork the socket to pend data.
         */
        fl4 = &inet->cork.fl.u.ip4;
        fl4->daddr = daddr;
        fl4->saddr = saddr;
        fl4->fl4_dport = dport;
        fl4->fl4_sport = inet->inet_sport;
        up->pending = AF_INET;

do_append_data:
        up->len += ulen;
        err = ip_append_data(sk, fl4, getfrag, msg, ulen,
                             sizeof(struct udphdr), &ipc, &rt,
                             corkreq ? msg->msg_flags|MSG_MORE : msg->msg_flags);
        if (err)
                udp_flush_pending_frames(sk);
        else if (!corkreq)
                err = udp_push_pending_frames(sk);
        else if (unlikely(skb_queue_empty(&sk->sk_write_queue)))
                up->pending = 0;
        release_sock(sk);

out:
        ip_rt_put(rt);
out_free:
        if (free)
                kfree(ipc.opt);
        if (!err)
                return len;
        /*
         * ENOBUFS = no kernel mem, SOCK_NOSPACE = no sndbuf space.  Reporting
         * ENOBUFS might not be good (it's not tunable per se), but otherwise
         * we don't have a good statistic (IpOutDiscards but it can be too many
         * things).  We could add another new stat but at least for now that
         * seems like overkill.
         */
        if (err == -ENOBUFS || test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
                UDP_INC_STATS(sock_net(sk),
                              UDP_MIB_SNDBUFERRORS, is_udplite);
        }
        return err;

do_confirm:
        if (msg->msg_flags & MSG_PROBE)
                dst_confirm_neigh(&rt->dst, &fl4->daddr);
        if (!(msg->msg_flags&MSG_PROBE) || len)
                goto back_from_confirm;
        err = 0;
        goto out;
}
EXPORT_SYMBOL(udp_sendmsg);

int udp_sendpage(struct sock *sk, struct page *page, int offset,
                 size_t size, int flags)
{
        struct inet_sock *inet = inet_sk(sk);
        struct udp_sock *up = udp_sk(sk);
        int ret;

        if (flags & MSG_SENDPAGE_NOTLAST)
                flags |= MSG_MORE;

        if (!up->pending) {
                struct msghdr msg = {   .msg_flags = flags|MSG_MORE };

                /* Call udp_sendmsg to specify destination address which
                 * sendpage interface can't pass.
                 * This will succeed only when the socket is connected.
                 */
                ret = udp_sendmsg(sk, &msg, 0);
                if (ret < 0)
                        return ret;
        }

        lock_sock(sk);

        if (unlikely(!up->pending)) {
                release_sock(sk);

                net_dbg_ratelimited("cork failed\n");
                return -EINVAL;
        }

        ret = ip_append_page(sk, &inet->cork.fl.u.ip4,
                             page, offset, size, flags);
        if (ret == -EOPNOTSUPP) {
                release_sock(sk);
                return sock_no_sendpage(sk->sk_socket, page, offset,
                                        size, flags);
        }
        if (ret < 0) {
                udp_flush_pending_frames(sk);
                goto out;
        }

        up->len += size;
        if (!(up->corkflag || (flags&MSG_MORE)))
                ret = udp_push_pending_frames(sk);
        if (!ret)
                ret = size;
out:
        release_sock(sk);
        return ret;
}

#define UDP_SKB_IS_STATELESS 0x80000000

/* all head states (dst, sk, nf conntrack) except skb extensions are
 * cleared by udp_rcv().
 *
 * We need to preserve secpath, if present, to eventually process
 * IP_CMSG_PASSSEC at recvmsg() time.
 *
 * Other extensions can be cleared.
 */
static bool udp_try_make_stateless(struct sk_buff *skb)
{
        if (!skb_has_extensions(skb))
                return true;

        if (!secpath_exists(skb)) {
                skb_ext_reset(skb);
                return true;
        }

        return false;
}

static void udp_set_dev_scratch(struct sk_buff *skb)
{
        struct udp_dev_scratch *scratch = udp_skb_scratch(skb);

        BUILD_BUG_ON(sizeof(struct udp_dev_scratch) > sizeof(long));
        scratch->_tsize_state = skb->truesize;
#if BITS_PER_LONG == 64
        scratch->len = skb->len;
        scratch->csum_unnecessary = !!skb_csum_unnecessary(skb);
        scratch->is_linear = !skb_is_nonlinear(skb);
#endif
        if (udp_try_make_stateless(skb))
                scratch->_tsize_state |= UDP_SKB_IS_STATELESS;
}

static void udp_skb_csum_unnecessary_set(struct sk_buff *skb)
{
        /* We come here after udp_lib_checksum_complete() returned 0.
         * This means that __skb_checksum_complete() might have
         * set skb->csum_valid to 1.
         * On 64bit platforms, we can set csum_unnecessary
         * to true, but only if the skb is not shared.
         */
#if BITS_PER_LONG == 64
        if (!skb_shared(skb))
                udp_skb_scratch(skb)->csum_unnecessary = true;
#endif
}

static int udp_skb_truesize(struct sk_buff *skb)
{
        return udp_skb_scratch(skb)->_tsize_state & ~UDP_SKB_IS_STATELESS;
}

static bool udp_skb_has_head_state(struct sk_buff *skb)
{
        return !(udp_skb_scratch(skb)->_tsize_state & UDP_SKB_IS_STATELESS);
}

/* fully reclaim rmem/fwd memory allocated for skb */
static void udp_rmem_release(struct sock *sk, int size, int partial,
                             bool rx_queue_lock_held)
{
        struct udp_sock *up = udp_sk(sk);
        struct sk_buff_head *sk_queue;
        int amt;

        if (likely(partial)) {
                up->forward_deficit += size;
                size = up->forward_deficit;
                if (size < (sk->sk_rcvbuf >> 2) &&
                    !skb_queue_empty(&up->reader_queue))
                        return;
        } else {
                size += up->forward_deficit;
        }
        up->forward_deficit = 0;

        /* acquire the sk_receive_queue for fwd allocated memory scheduling,
         * if the called don't held it already
         */
        sk_queue = &sk->sk_receive_queue;
        if (!rx_queue_lock_held)
                spin_lock(&sk_queue->lock);


        sk->sk_forward_alloc += size;
        amt = (sk->sk_forward_alloc - partial) & ~(SK_MEM_QUANTUM - 1);
        sk->sk_forward_alloc -= amt;

        if (amt)
                __sk_mem_reduce_allocated(sk, amt >> SK_MEM_QUANTUM_SHIFT);

        atomic_sub(size, &sk->sk_rmem_alloc);

        /* this can save us from acquiring the rx queue lock on next receive */
        skb_queue_splice_tail_init(sk_queue, &up->reader_queue);

        if (!rx_queue_lock_held)
                spin_unlock(&sk_queue->lock);
}

/* Note: called with reader_queue.lock held.
 * Instead of using skb->truesize here, find a copy of it in skb->dev_scratch
 * This avoids a cache line miss while receive_queue lock is held.
 * Look at __udp_enqueue_schedule_skb() to find where this copy is done.
 */
void udp_skb_destructor(struct sock *sk, struct sk_buff *skb)
{
        prefetch(&skb->data);
        udp_rmem_release(sk, udp_skb_truesize(skb), 1, false);
}
EXPORT_SYMBOL(udp_skb_destructor);

/* as above, but the caller held the rx queue lock, too */
static void udp_skb_dtor_locked(struct sock *sk, struct sk_buff *skb)
{
        prefetch(&skb->data);
        udp_rmem_release(sk, udp_skb_truesize(skb), 1, true);
}

/* Idea of busylocks is to let producers grab an extra spinlock
 * to relieve pressure on the receive_queue spinlock shared by consumer.
 * Under flood, this means that only one producer can be in line
 * trying to acquire the receive_queue spinlock.
 * These busylock can be allocated on a per cpu manner, instead of a
 * per socket one (that would consume a cache line per socket)
 */
static int udp_busylocks_log __read_mostly;
static spinlock_t *udp_busylocks __read_mostly;

static spinlock_t *busylock_acquire(void *ptr)
{
        spinlock_t *busy;

        busy = udp_busylocks + hash_ptr(ptr, udp_busylocks_log);
        spin_lock(busy);
        return busy;
}

static void busylock_release(spinlock_t *busy)
{
        if (busy)
                spin_unlock(busy);
}

int __udp_enqueue_schedule_skb(struct sock *sk, struct sk_buff *skb)
{
        struct sk_buff_head *list = &sk->sk_receive_queue;
        int rmem, delta, amt, err = -ENOMEM;
        spinlock_t *busy = NULL;
        int size;

        /* try to avoid the costly atomic add/sub pair when the receive
         * queue is full; always allow at least a packet
         */
        rmem = atomic_read(&sk->sk_rmem_alloc);
        if (rmem > sk->sk_rcvbuf)
                goto drop;

        /* Under mem pressure, it might be helpful to help udp_recvmsg()
         * having linear skbs :
         * - Reduce memory overhead and thus increase receive queue capacity
         * - Less cache line misses at copyout() time
         * - Less work at consume_skb() (less alien page frag freeing)
         */
        if (rmem > (sk->sk_rcvbuf >> 1)) {
                skb_condense(skb);

                busy = busylock_acquire(sk);
        }
        size = skb->truesize;
        udp_set_dev_scratch(skb);

        /* we drop only if the receive buf is full and the receive
         * queue contains some other skb
         */
        rmem = atomic_add_return(size, &sk->sk_rmem_alloc);
        if (rmem > (size + (unsigned int)sk->sk_rcvbuf))
                goto uncharge_drop;

        spin_lock(&list->lock);
        if (size >= sk->sk_forward_alloc) {
                amt = sk_mem_pages(size);
                delta = amt << SK_MEM_QUANTUM_SHIFT;
                if (!__sk_mem_raise_allocated(sk, delta, amt, SK_MEM_RECV)) {
                        err = -ENOBUFS;
                        spin_unlock(&list->lock);
                        goto uncharge_drop;
                }

                sk->sk_forward_alloc += delta;
        }

        sk->sk_forward_alloc -= size;

        /* no need to setup a destructor, we will explicitly release the
         * forward allocated memory on dequeue
         */
        sock_skb_set_dropcount(sk, skb);

        __skb_queue_tail(list, skb);
        spin_unlock(&list->lock);

        if (!sock_flag(sk, SOCK_DEAD))
                sk->sk_data_ready(sk);

        busylock_release(busy);
        return 0;

uncharge_drop:
        atomic_sub(skb->truesize, &sk->sk_rmem_alloc);

drop:
        atomic_inc(&sk->sk_drops);
        busylock_release(busy);
        return err;
}
EXPORT_SYMBOL_GPL(__udp_enqueue_schedule_skb);

void udp_destruct_sock(struct sock *sk)
{
        /* reclaim completely the forward allocated memory */
        struct udp_sock *up = udp_sk(sk);
        unsigned int total = 0;
        struct sk_buff *skb;

        skb_queue_splice_tail_init(&sk->sk_receive_queue, &up->reader_queue);
        while ((skb = __skb_dequeue(&up->reader_queue)) != NULL) {
                total += skb->truesize;
                kfree_skb(skb);
        }
        udp_rmem_release(sk, total, 0, true);

        inet_sock_destruct(sk);
}
EXPORT_SYMBOL_GPL(udp_destruct_sock);

int udp_init_sock(struct sock *sk)
{
        skb_queue_head_init(&udp_sk(sk)->reader_queue);
        sk->sk_destruct = udp_destruct_sock;
        return 0;
}
EXPORT_SYMBOL_GPL(udp_init_sock);

void skb_consume_udp(struct sock *sk, struct sk_buff *skb, int len)
{
        if (unlikely(READ_ONCE(sk->sk_peek_off) >= 0)) {
                bool slow = lock_sock_fast(sk);

                sk_peek_offset_bwd(sk, len);
                unlock_sock_fast(sk, slow);
        }

        if (!skb_unref(skb))
                return;

        /* In the more common cases we cleared the head states previously,
         * see __udp_queue_rcv_skb().
         */
        if (unlikely(udp_skb_has_head_state(skb)))
                skb_release_head_state(skb);
        __consume_stateless_skb(skb);
}
EXPORT_SYMBOL_GPL(skb_consume_udp);

static struct sk_buff *__first_packet_length(struct sock *sk,
                                             struct sk_buff_head *rcvq,
                                             int *total)
{
        struct sk_buff *skb;

        while ((skb = skb_peek(rcvq)) != NULL) {
                if (udp_lib_checksum_complete(skb)) {
                        __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
                                        IS_UDPLITE(sk));
                        __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
                                        IS_UDPLITE(sk));
                        atomic_inc(&sk->sk_drops);
                        __skb_unlink(skb, rcvq);
                        *total += skb->truesize;
                        kfree_skb(skb);
                } else {
                        udp_skb_csum_unnecessary_set(skb);
                        break;
                }
        }
        return skb;
}

/**
 *      first_packet_length     - return length of first packet in receive queue
 *      @sk: socket
 *
 *      Drops all bad checksum frames, until a valid one is found.
 *      Returns the length of found skb, or -1 if none is found.
 */
static int first_packet_length(struct sock *sk)
{
        struct sk_buff_head *rcvq = &udp_sk(sk)->reader_queue;
        struct sk_buff_head *sk_queue = &sk->sk_receive_queue;
        struct sk_buff *skb;
        int total = 0;
        int res;

        spin_lock_bh(&rcvq->lock);
        skb = __first_packet_length(sk, rcvq, &total);
        if (!skb && !skb_queue_empty_lockless(sk_queue)) {
                spin_lock(&sk_queue->lock);
                skb_queue_splice_tail_init(sk_queue, rcvq);
                spin_unlock(&sk_queue->lock);

                skb = __first_packet_length(sk, rcvq, &total);
        }
        res = skb ? skb->len : -1;
        if (total)
                udp_rmem_release(sk, total, 1, false);
        spin_unlock_bh(&rcvq->lock);
        return res;
}

/*
 *      IOCTL requests applicable to the UDP protocol
 */

int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
{
        switch (cmd) {
        case SIOCOUTQ:
        {
                int amount = sk_wmem_alloc_get(sk);

                return put_user(amount, (int __user *)arg);
        }

        case SIOCINQ:
        {
                int amount = max_t(int, 0, first_packet_length(sk));

                return put_user(amount, (int __user *)arg);
        }

        default:
                return -ENOIOCTLCMD;
        }

        return 0;
}
EXPORT_SYMBOL(udp_ioctl);

struct sk_buff *__skb_recv_udp(struct sock *sk, unsigned int flags,
                               int noblock, int *off, int *err)
{
        struct sk_buff_head *sk_queue = &sk->sk_receive_queue;
        struct sk_buff_head *queue;
        struct sk_buff *last;
        long timeo;
        int error;

        queue = &udp_sk(sk)->reader_queue;
        flags |= noblock ? MSG_DONTWAIT : 0;
        timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT);
        do {
                struct sk_buff *skb;

                error = sock_error(sk);
                if (error)
                        break;

                error = -EAGAIN;
                do {
                        spin_lock_bh(&queue->lock);
                        skb = __skb_try_recv_from_queue(sk, queue, flags, off,
                                                        err, &last);
                        if (skb) {
                                if (!(flags & MSG_PEEK))
                                        udp_skb_destructor(sk, skb);
                                spin_unlock_bh(&queue->lock);
                                return skb;
                        }

                        if (skb_queue_empty_lockless(sk_queue)) {
                                spin_unlock_bh(&queue->lock);
                                goto busy_check;
                        }

                        /* refill the reader queue and walk it again
                         * keep both queues locked to avoid re-acquiring
                         * the sk_receive_queue lock if fwd memory scheduling
                         * is needed.
                         */
                        spin_lock(&sk_queue->lock);
                        skb_queue_splice_tail_init(sk_queue, queue);

                        skb = __skb_try_recv_from_queue(sk, queue, flags, off,
                                                        err, &last);
                        if (skb && !(flags & MSG_PEEK))
                                udp_skb_dtor_locked(sk, skb);
                        spin_unlock(&sk_queue->lock);
                        spin_unlock_bh(&queue->lock);
                        if (skb)
                                return skb;

busy_check:
                        if (!sk_can_busy_loop(sk))
                                break;

                        sk_busy_loop(sk, flags & MSG_DONTWAIT);
                } while (!skb_queue_empty_lockless(sk_queue));

                /* sk_queue is empty, reader_queue may contain peeked packets */
        } while (timeo &&
                 !__skb_wait_for_more_packets(sk, &sk->sk_receive_queue,
                                              &error, &timeo,
                                              (struct sk_buff *)sk_queue));

        *err = error;
        return NULL;
}
EXPORT_SYMBOL(__skb_recv_udp);

int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
                  sk_read_actor_t recv_actor)
{
        int copied = 0;

        while (1) {
                struct sk_buff *skb;
                int err, used;

                skb = skb_recv_udp(sk, 0, 1, &err);
                if (!skb)
                        return err;
                used = recv_actor(desc, skb, 0, skb->len);
                if (used <= 0) {
                        if (!copied)
                                copied = used;
                        break;
                } else if (used <= skb->len) {
                        copied += used;
                }

                if (!desc->count)
                        break;
        }

        return copied;
}
EXPORT_SYMBOL(udp_read_sock);

/*
 *      This should be easy, if there is something there we
 *      return it, otherwise we block.
 */

int udp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int noblock,
                int flags, int *addr_len)
{
        struct inet_sock *inet = inet_sk(sk);
        DECLARE_SOCKADDR(struct sockaddr_in *, sin, msg->msg_name);
        struct sk_buff *skb;
        unsigned int ulen, copied;
        int off, err, peeking = flags & MSG_PEEK;
        int is_udplite = IS_UDPLITE(sk);
        bool checksum_valid = false;

        if (flags & MSG_ERRQUEUE)
                return ip_recv_error(sk, msg, len, addr_len);

try_again:
        off = sk_peek_offset(sk, flags);
        skb = __skb_recv_udp(sk, flags, noblock, &off, &err);
        if (!skb)
                return err;

        ulen = udp_skb_len(skb);
        copied = len;
        if (copied > ulen - off)
                copied = ulen - off;
        else if (copied < ulen)
                msg->msg_flags |= MSG_TRUNC;

        /*
         * If checksum is needed at all, try to do it while copying the
         * data.  If the data is truncated, or if we only want a partial
         * coverage checksum (UDP-Lite), do it before the copy.
         */

        if (copied < ulen || peeking ||
            (is_udplite && UDP_SKB_CB(skb)->partial_cov)) {
                checksum_valid = udp_skb_csum_unnecessary(skb) ||
                                !__udp_lib_checksum_complete(skb);
                if (!checksum_valid)
                        goto csum_copy_err;
        }

        if (checksum_valid || udp_skb_csum_unnecessary(skb)) {
                if (udp_skb_is_linear(skb))
                        err = copy_linear_skb(skb, copied, off, &msg->msg_iter);
                else
                        err = skb_copy_datagram_msg(skb, off, msg, copied);
        } else {
                err = skb_copy_and_csum_datagram_msg(skb, off, msg);

                if (err == -EINVAL)
                        goto csum_copy_err;
        }

        if (unlikely(err)) {
                if (!peeking) {
                        atomic_inc(&sk->sk_drops);
                        UDP_INC_STATS(sock_net(sk),
                                      UDP_MIB_INERRORS, is_udplite);
                }
                kfree_skb(skb);
                return err;
        }

        if (!peeking)
                UDP_INC_STATS(sock_net(sk),
                              UDP_MIB_INDATAGRAMS, is_udplite);

        sock_recv_ts_and_drops(msg, sk, skb);

        /* Copy the address. */
        if (sin) {
                sin->sin_family = AF_INET;
                sin->sin_port = udp_hdr(skb)->source;
                sin->sin_addr.s_addr = ip_hdr(skb)->saddr;
                memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
                *addr_len = sizeof(*sin);

                BPF_CGROUP_RUN_PROG_UDP4_RECVMSG_LOCK(sk,
                                                      (struct sockaddr *)sin);
        }

        if (udp_sk(sk)->gro_enabled)
                udp_cmsg_recv(msg, sk, skb);

        if (inet->cmsg_flags)
                ip_cmsg_recv_offset(msg, sk, skb, sizeof(struct udphdr), off);

        err = copied;
        if (flags & MSG_TRUNC)
                err = ulen;

        skb_consume_udp(sk, skb, peeking ? -err : err);
        return err;

csum_copy_err:
        if (!__sk_queue_drop_skb(sk, &udp_sk(sk)->reader_queue, skb, flags,
                                 udp_skb_destructor)) {
                UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
                UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
        }
        kfree_skb(skb);

        /* starting over for a new packet, but check if we need to yield */
        cond_resched();
        msg->msg_flags &= ~MSG_TRUNC;
        goto try_again;
}

int udp_pre_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
{
        /* This check is replicated from __ip4_datagram_connect() and
         * intended to prevent BPF program called below from accessing bytes
         * that are out of the bound specified by user in addr_len.
         */
        if (addr_len < sizeof(struct sockaddr_in))
                return -EINVAL;

        return BPF_CGROUP_RUN_PROG_INET4_CONNECT_LOCK(sk, uaddr);
}
EXPORT_SYMBOL(udp_pre_connect);

int __udp_disconnect(struct sock *sk, int flags)
{
        struct inet_sock *inet = inet_sk(sk);
        /*
         *      1003.1g - break association.
         */

        sk->sk_state = TCP_CLOSE;
        inet->inet_daddr = 0;
        inet->inet_dport = 0;
        sock_rps_reset_rxhash(sk);
        sk->sk_bound_dev_if = 0;
        if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK)) {
                inet_reset_saddr(sk);
                if (sk->sk_prot->rehash &&
                    (sk->sk_userlocks & SOCK_BINDPORT_LOCK))
                        sk->sk_prot->rehash(sk);
        }

        if (!(sk->sk_userlocks & SOCK_BINDPORT_LOCK)) {
                sk->sk_prot->unhash(sk);
                inet->inet_sport = 0;
        }
        sk_dst_reset(sk);
        return 0;
}
EXPORT_SYMBOL(__udp_disconnect);

int udp_disconnect(struct sock *sk, int flags)
{
        lock_sock(sk);
        __udp_disconnect(sk, flags);
        release_sock(sk);
        return 0;
}
EXPORT_SYMBOL(udp_disconnect);

void udp_lib_unhash(struct sock *sk)
{
        if (sk_hashed(sk)) {
                struct udp_table *udptable = sk->sk_prot->h.udp_table;
                struct udp_hslot *hslot, *hslot2;

                hslot  = udp_hashslot(udptable, sock_net(sk),
                                      udp_sk(sk)->udp_port_hash);
                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);

                spin_lock_bh(&hslot->lock);
                if (rcu_access_pointer(sk->sk_reuseport_cb))
                        reuseport_detach_sock(sk);
                if (sk_del_node_init_rcu(sk)) {
                        hslot->count--;
                        inet_sk(sk)->inet_num = 0;
                        sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);

                        spin_lock(&hslot2->lock);
                        hlist_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
                        hslot2->count--;
                        spin_unlock(&hslot2->lock);
                }
                spin_unlock_bh(&hslot->lock);
        }
}
EXPORT_SYMBOL(udp_lib_unhash);

/*
 * inet_rcv_saddr was changed, we must rehash secondary hash
 */
void udp_lib_rehash(struct sock *sk, u16 newhash)
{
        if (sk_hashed(sk)) {
                struct udp_table *udptable = sk->sk_prot->h.udp_table;
                struct udp_hslot *hslot, *hslot2, *nhslot2;

                hslot2 = udp_hashslot2(udptable, udp_sk(sk)->udp_portaddr_hash);
                nhslot2 = udp_hashslot2(udptable, newhash);
                udp_sk(sk)->udp_portaddr_hash = newhash;

                if (hslot2 != nhslot2 ||
                    rcu_access_pointer(sk->sk_reuseport_cb)) {
                        hslot = udp_hashslot(udptable, sock_net(sk),
                                             udp_sk(sk)->udp_port_hash);
                        /* we must lock primary chain too */
                        spin_lock_bh(&hslot->lock);
                        if (rcu_access_pointer(sk->sk_reuseport_cb))
                                reuseport_detach_sock(sk);

                        if (hslot2 != nhslot2) {
                                spin_lock(&hslot2->lock);
                                hlist_del_init_rcu(&udp_sk(sk)->udp_portaddr_node);
                                hslot2->count--;
                                spin_unlock(&hslot2->lock);

                                spin_lock(&nhslot2->lock);
                                hlist_add_head_rcu(&udp_sk(sk)->udp_portaddr_node,
                                                         &nhslot2->head);
                                nhslot2->count++;
                                spin_unlock(&nhslot2->lock);
                        }

                        spin_unlock_bh(&hslot->lock);
                }
        }
}
EXPORT_SYMBOL(udp_lib_rehash);

void udp_v4_rehash(struct sock *sk)
{
        u16 new_hash = ipv4_portaddr_hash(sock_net(sk),
                                          inet_sk(sk)->inet_rcv_saddr,
                                          inet_sk(sk)->inet_num);
        udp_lib_rehash(sk, new_hash);
}

static int __udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
        int rc;

        if (inet_sk(sk)->inet_daddr) {
                sock_rps_save_rxhash(sk, skb);
                sk_mark_napi_id(sk, skb);
                sk_incoming_cpu_update(sk);
        } else {
                sk_mark_napi_id_once(sk, skb);
        }

        rc = __udp_enqueue_schedule_skb(sk, skb);
        if (rc < 0) {
                int is_udplite = IS_UDPLITE(sk);

                /* Note that an ENOMEM error is charged twice */
                if (rc == -ENOMEM)
                        UDP_INC_STATS(sock_net(sk), UDP_MIB_RCVBUFERRORS,
                                        is_udplite);
                else
                        UDP_INC_STATS(sock_net(sk), UDP_MIB_MEMERRORS,
                                      is_udplite);
                UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
                kfree_skb(skb);
                trace_udp_fail_queue_rcv_skb(rc, sk);
                return -1;
        }

        return 0;
}

/* returns:
 *  -1: error
 *   0: success
 *  >0: "udp encap" protocol resubmission
 *
 * Note that in the success and error cases, the skb is assumed to
 * have either been requeued or freed.
 */
static int udp_queue_rcv_one_skb(struct sock *sk, struct sk_buff *skb)
{
        struct udp_sock *up = udp_sk(sk);
        int is_udplite = IS_UDPLITE(sk);

        /*
         *      Charge it to the socket, dropping if the queue is full.
         */
        if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
                goto drop;
        nf_reset_ct(skb);

        if (static_branch_unlikely(&udp_encap_needed_key) && up->encap_type) {
                int (*encap_rcv)(struct sock *sk, struct sk_buff *skb);

                /*
                 * This is an encapsulation socket so pass the skb to
                 * the socket's udp_encap_rcv() hook. Otherwise, just
                 * fall through and pass this up the UDP socket.
                 * up->encap_rcv() returns the following value:
                 * =0 if skb was successfully passed to the encap
                 *    handler or was discarded by it.
                 * >0 if skb should be passed on to UDP.
                 * <0 if skb should be resubmitted as proto -N
                 */

                /* if we're overly short, let UDP handle it */
                encap_rcv = READ_ONCE(up->encap_rcv);
                if (encap_rcv) {
                        int ret;

                        /* Verify checksum before giving to encap */
                        if (udp_lib_checksum_complete(skb))
                                goto csum_error;

                        ret = encap_rcv(sk, skb);
                        if (ret <= 0) {
                                __UDP_INC_STATS(sock_net(sk),
                                                UDP_MIB_INDATAGRAMS,
                                                is_udplite);
                                return -ret;
                        }
                }

                /* FALLTHROUGH -- it's a UDP Packet */
        }

        /*
         *      UDP-Lite specific tests, ignored on UDP sockets
         */
        if ((up->pcflag & UDPLITE_RECV_CC)  &&  UDP_SKB_CB(skb)->partial_cov) {

                /*
                 * MIB statistics other than incrementing the error count are
                 * disabled for the following two types of errors: these depend
                 * on the application settings, not on the functioning of the
                 * protocol stack as such.
                 *
                 * RFC 3828 here recommends (sec 3.3): "There should also be a
                 * way ... to ... at least let the receiving application block
                 * delivery of packets with coverage values less than a value
                 * provided by the application."
                 */
                if (up->pcrlen == 0) {          /* full coverage was set  */
                        net_dbg_ratelimited("UDPLite: partial coverage %d while full coverage %d requested\n",
                                            UDP_SKB_CB(skb)->cscov, skb->len);
                        goto drop;
                }
                /* The next case involves violating the min. coverage requested
                 * by the receiver. This is subtle: if receiver wants x and x is
                 * greater than the buffersize/MTU then receiver will complain
                 * that it wants x while sender emits packets of smaller size y.
                 * Therefore the above ...()->partial_cov statement is essential.
                 */
                if (UDP_SKB_CB(skb)->cscov  <  up->pcrlen) {
                        net_dbg_ratelimited("UDPLite: coverage %d too small, need min %d\n",
                                            UDP_SKB_CB(skb)->cscov, up->pcrlen);
                        goto drop;
                }
        }

        prefetch(&sk->sk_rmem_alloc);
        if (rcu_access_pointer(sk->sk_filter) &&
            udp_lib_checksum_complete(skb))
                        goto csum_error;

        if (sk_filter_trim_cap(sk, skb, sizeof(struct udphdr)))
                goto drop;

        udp_csum_pull_header(skb);

        ipv4_pktinfo_prepare(sk, skb);
        return __udp_queue_rcv_skb(sk, skb);

csum_error:
        __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS, is_udplite);
drop:
        __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS, is_udplite);
        atomic_inc(&sk->sk_drops);
        kfree_skb(skb);
        return -1;
}

static int udp_queue_rcv_skb(struct sock *sk, struct sk_buff *skb)
{
        struct sk_buff *next, *segs;
        int ret;

        if (likely(!udp_unexpected_gso(sk, skb)))
                return udp_queue_rcv_one_skb(sk, skb);

        BUILD_BUG_ON(sizeof(struct udp_skb_cb) > SKB_GSO_CB_OFFSET);
        __skb_push(skb, -skb_mac_offset(skb));
        segs = udp_rcv_segment(sk, skb, true);
        skb_list_walk_safe(segs, skb, next) {
                __skb_pull(skb, skb_transport_offset(skb));

                udp_post_segment_fix_csum(skb);
                ret = udp_queue_rcv_one_skb(sk, skb);
                if (ret > 0)
                        ip_protocol_deliver_rcu(dev_net(skb->dev), skb, ret);
        }
        return 0;
}

/* For TCP sockets, sk_rx_dst is protected by socket lock
 * For UDP, we use xchg() to guard against concurrent changes.
 */
bool udp_sk_rx_dst_set(struct sock *sk, struct dst_entry *dst)
{
        struct dst_entry *old;

        if (dst_hold_safe(dst)) {
                old = xchg(&sk->sk_rx_dst, dst);
                dst_release(old);
                return old != dst;
        }
        return false;
}
EXPORT_SYMBOL(udp_sk_rx_dst_set);

/*
 *      Multicasts and broadcasts go to each listener.
 *
 *      Note: called only from the BH handler context.
 */
static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
                                    struct udphdr  *uh,
                                    __be32 saddr, __be32 daddr,
                                    struct udp_table *udptable,
                                    int proto)
{
        struct sock *sk, *first = NULL;
        unsigned short hnum = ntohs(uh->dest);
        struct udp_hslot *hslot = udp_hashslot(udptable, net, hnum);
        unsigned int hash2 = 0, hash2_any = 0, use_hash2 = (hslot->count > 10);
        unsigned int offset = offsetof(typeof(*sk), sk_node);
        int dif = skb->dev->ifindex;
        int sdif = inet_sdif(skb);
        struct hlist_node *node;
        struct sk_buff *nskb;

        if (use_hash2) {
                hash2_any = ipv4_portaddr_hash(net, htonl(INADDR_ANY), hnum) &
                            udptable->mask;
                hash2 = ipv4_portaddr_hash(net, daddr, hnum) & udptable->mask;
start_lookup:
                hslot = &udptable->hash2[hash2];
                offset = offsetof(typeof(*sk), __sk_common.skc_portaddr_node);
        }

        sk_for_each_entry_offset_rcu(sk, node, &hslot->head, offset) {
                if (!__udp_is_mcast_sock(net, sk, uh->dest, daddr,
                                         uh->source, saddr, dif, sdif, hnum))
                        continue;

                if (!first) {
                        first = sk;
                        continue;
                }
                nskb = skb_clone(skb, GFP_ATOMIC);

                if (unlikely(!nskb)) {
                        atomic_inc(&sk->sk_drops);
                        __UDP_INC_STATS(net, UDP_MIB_RCVBUFERRORS,
                                        IS_UDPLITE(sk));
                        __UDP_INC_STATS(net, UDP_MIB_INERRORS,
                                        IS_UDPLITE(sk));
                        continue;
                }
                if (udp_queue_rcv_skb(sk, nskb) > 0)
                        consume_skb(nskb);
        }

        /* Also lookup *:port if we are using hash2 and haven't done so yet. */
        if (use_hash2 && hash2 != hash2_any) {
                hash2 = hash2_any;
                goto start_lookup;
        }

        if (first) {
                if (udp_queue_rcv_skb(first, skb) > 0)
                        consume_skb(skb);
        } else {
                kfree_skb(skb);
                __UDP_INC_STATS(net, UDP_MIB_IGNOREDMULTI,
                                proto == IPPROTO_UDPLITE);
        }
        return 0;
}

/* Initialize UDP checksum. If exited with zero value (success),
 * CHECKSUM_UNNECESSARY means, that no more checks are required.
 * Otherwise, csum completion requires checksumming packet body,
 * including udp header and folding it to skb->csum.
 */
static inline int udp4_csum_init(struct sk_buff *skb, struct udphdr *uh,
                                 int proto)
{
        int err;

        UDP_SKB_CB(skb)->partial_cov = 0;
        UDP_SKB_CB(skb)->cscov = skb->len;

        if (proto == IPPROTO_UDPLITE) {
                err = udplite_checksum_init(skb, uh);
                if (err)
                        return err;

                if (UDP_SKB_CB(skb)->partial_cov) {
                        skb->csum = inet_compute_pseudo(skb, proto);
                        return 0;
                }
        }

        /* Note, we are only interested in != 0 or == 0, thus the
         * force to int.
         */
        err = (__force int)skb_checksum_init_zero_check(skb, proto, uh->check,
                                                        inet_compute_pseudo);
        if (err)
                return err;

        if (skb->ip_summed == CHECKSUM_COMPLETE && !skb->csum_valid) {
                /* If SW calculated the value, we know it's bad */
                if (skb->csum_complete_sw)
                        return 1;

                /* HW says the value is bad. Let's validate that.
                 * skb->csum is no longer the full packet checksum,
                 * so don't treat it as such.
                 */
                skb_checksum_complete_unset(skb);
        }

        return 0;
}

/* wrapper for udp_queue_rcv_skb tacking care of csum conversion and
 * return code conversion for ip layer consumption
 */
static int udp_unicast_rcv_skb(struct sock *sk, struct sk_buff *skb,
                               struct udphdr *uh)
{
        int ret;

        if (inet_get_convert_csum(sk) && uh->check && !IS_UDPLITE(sk))
                skb_checksum_try_convert(skb, IPPROTO_UDP, inet_compute_pseudo);

        ret = udp_queue_rcv_skb(sk, skb);

        /* a return value > 0 means to resubmit the input, but
         * it wants the return to be -protocol, or 0
         */
        if (ret > 0)
                return -ret;
        return 0;
}

/*
 *      All we need to do is get the socket, and then do a checksum.
 */

int __udp4_lib_rcv(struct sk_buff *skb, struct udp_table *udptable,
                   int proto)
{
        struct sock *sk;
        struct udphdr *uh;
        unsigned short ulen;
        struct rtable *rt = skb_rtable(skb);
        __be32 saddr, daddr;
        struct net *net = dev_net(skb->dev);
        bool refcounted;

        /*
         *  Validate the packet.
         */
        if (!pskb_may_pull(skb, sizeof(struct udphdr)))
                goto drop;              /* No space for header. */

        uh   = udp_hdr(skb);
        ulen = ntohs(uh->len);
        saddr = ip_hdr(skb)->saddr;
        daddr = ip_hdr(skb)->daddr;

        if (ulen > skb->len)
                goto short_packet;

        if (proto == IPPROTO_UDP) {
                /* UDP validates ulen. */
                if (ulen < sizeof(*uh) || pskb_trim_rcsum(skb, ulen))
                        goto short_packet;
                uh = udp_hdr(skb);
        }

        if (udp4_csum_init(skb, uh, proto))
                goto csum_error;

        sk = skb_steal_sock(skb, &refcounted);
        if (sk) {
                struct dst_entry *dst = skb_dst(skb);
                int ret;

                if (unlikely(sk->sk_rx_dst != dst))
                        udp_sk_rx_dst_set(sk, dst);

                ret = udp_unicast_rcv_skb(sk, skb, uh);
                if (refcounted)
                        sock_put(sk);
                return ret;
        }

        if (rt->rt_flags & (RTCF_BROADCAST|RTCF_MULTICAST))
                return __udp4_lib_mcast_deliver(net, skb, uh,
                                                saddr, daddr, udptable, proto);

        sk = __udp4_lib_lookup_skb(skb, uh->source, uh->dest, udptable);
        if (sk)
                return udp_unicast_rcv_skb(sk, skb, uh);

        if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
                goto drop;
        nf_reset_ct(skb);

        /* No socket. Drop packet silently, if checksum is wrong */
        if (udp_lib_checksum_complete(skb))
                goto csum_error;

        __UDP_INC_STATS(net, UDP_MIB_NOPORTS, proto == IPPROTO_UDPLITE);
        icmp_send(skb, ICMP_DEST_UNREACH, ICMP_PORT_UNREACH, 0);

        /*
         * Hmm.  We got an UDP packet to a port to which we
         * don't wanna listen.  Ignore it.
         */
        kfree_skb(skb);
        return 0;

short_packet:
        net_dbg_ratelimited("UDP%s: short packet: From %pI4:%u %d/%d to %pI4:%u\n",
                            proto == IPPROTO_UDPLITE ? "Lite" : "",
                            &saddr, ntohs(uh->source),
                            ulen, skb->len,
                            &daddr, ntohs(uh->dest));
        goto drop;

csum_error:
        /*
         * RFC1122: OK.  Discards the bad packet silently (as far as
         * the network is concerned, anyway) as per 4.1.3.4 (MUST).
         */
        net_dbg_ratelimited("UDP%s: bad checksum. From %pI4:%u to %pI4:%u ulen %d\n",
                            proto == IPPROTO_UDPLITE ? "Lite" : "",
                            &saddr, ntohs(uh->source), &daddr, ntohs(uh->dest),
                            ulen);
        __UDP_INC_STATS(net, UDP_MIB_CSUMERRORS, proto == IPPROTO_UDPLITE);
drop:
        __UDP_INC_STATS(net, UDP_MIB_INERRORS, proto == IPPROTO_UDPLITE);
        kfree_skb(skb);
        return 0;
}

/* We can only early demux multicast if there is a single matching socket.
 * If more than one socket found returns NULL
 */
static struct sock *__udp4_lib_mcast_demux_lookup(struct net *net,
                                                  __be16 loc_port, __be32 loc_addr,
                                                  __be16 rmt_port, __be32 rmt_addr,
                                                  int dif, int sdif)
{
        struct sock *sk, *result;
        unsigned short hnum = ntohs(loc_port);
        unsigned int slot = udp_hashfn(net, hnum, udp_table.mask);
        struct udp_hslot *hslot = &udp_table.hash[slot];

        /* Do not bother scanning a too big list */
        if (hslot->count > 10)
                return NULL;

        result = NULL;
        sk_for_each_rcu(sk, &hslot->head) {
                if (__udp_is_mcast_sock(net, sk, loc_port, loc_addr,
                                        rmt_port, rmt_addr, dif, sdif, hnum)) {
                        if (result)
                                return NULL;
                        result = sk;
                }
        }

        return result;
}

/* For unicast we should only early demux connected sockets or we can
 * break forwarding setups.  The chains here can be long so only check
 * if the first socket is an exact match and if not move on.
 */
static struct sock *__udp4_lib_demux_lookup(struct net *net,
                                            __be16 loc_port, __be32 loc_addr,
                                            __be16 rmt_port, __be32 rmt_addr,
                                            int dif, int sdif)
{
        unsigned short hnum = ntohs(loc_port);
        unsigned int hash2 = ipv4_portaddr_hash(net, loc_addr, hnum);
        unsigned int slot2 = hash2 & udp_table.mask;
        struct udp_hslot *hslot2 = &udp_table.hash2[slot2];
        INET_ADDR_COOKIE(acookie, rmt_addr, loc_addr);
        const __portpair ports = INET_COMBINED_PORTS(rmt_port, hnum);
        struct sock *sk;

        udp_portaddr_for_each_entry_rcu(sk, &hslot2->head) {
                if (INET_MATCH(sk, net, acookie, rmt_addr,
                               loc_addr, ports, dif, sdif))
                        return sk;
                /* Only check first socket in chain */
                break;
        }
        return NULL;
}

int udp_v4_early_demux(struct sk_buff *skb)
{
        struct net *net = dev_net(skb->dev);
        struct in_device *in_dev = NULL;
        const struct iphdr *iph;
        const struct udphdr *uh;
        struct sock *sk = NULL;
        struct dst_entry *dst;
        int dif = skb->dev->ifindex;
        int sdif = inet_sdif(skb);
        int ours;

        /* validate the packet */
        if (!pskb_may_pull(skb, skb_transport_offset(skb) + sizeof(struct udphdr)))
                return 0;

        iph = ip_hdr(skb);
        uh = udp_hdr(skb);

        if (skb->pkt_type == PACKET_MULTICAST) {
                in_dev = __in_dev_get_rcu(skb->dev);

                if (!in_dev)
                        return 0;

                ours = ip_check_mc_rcu(in_dev, iph->daddr, iph->saddr,
                                       iph->protocol);
                if (!ours)
                        return 0;

                sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
                                                   uh->source, iph->saddr,
                                                   dif, sdif);
        } else if (skb->pkt_type == PACKET_HOST) {
                sk = __udp4_lib_demux_lookup(net, uh->dest, iph->daddr,
                                             uh->source, iph->saddr, dif, sdif);
        }

        if (!sk || !refcount_inc_not_zero(&sk->sk_refcnt))
                return 0;

        skb->sk = sk;
        skb->destructor = sock_efree;
        dst = READ_ONCE(sk->sk_rx_dst);

        if (dst)
                dst = dst_check(dst, 0);
        if (dst) {
                u32 itag = 0;

                /* set noref for now.
                 * any place which wants to hold dst has to call
                 * dst_hold_safe()
                 */
                skb_dst_set_noref(skb, dst);

                /* for unconnected multicast sockets we need to validate
                 * the source on each packet
                 */
                if (!inet_sk(sk)->inet_daddr && in_dev)
                        return ip_mc_validate_source(skb, iph->daddr,
                                                     iph->saddr,
                                                     iph->tos & IPTOS_RT_MASK,
                                                     skb->dev, in_dev, &itag);
        }
        return 0;
}

int udp_rcv(struct sk_buff *skb)
{
        return __udp4_lib_rcv(skb, &udp_table, IPPROTO_UDP);
}

void udp_destroy_sock(struct sock *sk)
{
        struct udp_sock *up = udp_sk(sk);
        bool slow = lock_sock_fast(sk);
        udp_flush_pending_frames(sk);
        unlock_sock_fast(sk, slow);
        if (static_branch_unlikely(&udp_encap_needed_key)) {
                if (up->encap_type) {
                        void (*encap_destroy)(struct sock *sk);
                        encap_destroy = READ_ONCE(up->encap_destroy);
                        if (encap_destroy)
                                encap_destroy(sk);
                }
                if (up->encap_enabled)
                        static_branch_dec(&udp_encap_needed_key);
        }
}

/*
 *      Socket option code for UDP
 */
int udp_lib_setsockopt(struct sock *sk, int level, int optname,
                       sockptr_t optval, unsigned int optlen,
                       int (*push_pending_frames)(struct sock *))
{
        struct udp_sock *up = udp_sk(sk);
        int val, valbool;
        int err = 0;
        int is_udplite = IS_UDPLITE(sk);

        if (optlen < sizeof(int))
                return -EINVAL;

        if (copy_from_sockptr(&val, optval, sizeof(val)))
                return -EFAULT;

        valbool = val ? 1 : 0;

        switch (optname) {
        case UDP_CORK:
                if (val != 0) {
                        up->corkflag = 1;
                } else {
                        up->corkflag = 0;
                        lock_sock(sk);
                        push_pending_frames(sk);
                        release_sock(sk);
                }
                break;

        case UDP_ENCAP:
                switch (val) {
                case 0:
#ifdef CONFIG_XFRM
                case UDP_ENCAP_ESPINUDP:
                case UDP_ENCAP_ESPINUDP_NON_IKE:
#if IS_ENABLED(CONFIG_IPV6)
                        if (sk->sk_family == AF_INET6)
                                up->encap_rcv = ipv6_stub->xfrm6_udp_encap_rcv;
                        else
#endif
                                up->encap_rcv = xfrm4_udp_encap_rcv;
#endif
                        fallthrough;
                case UDP_ENCAP_L2TPINUDP:
                        up->encap_type = val;
                        lock_sock(sk);
                        udp_tunnel_encap_enable(sk->sk_socket);
                        release_sock(sk);
                        break;
                default:
                        err = -ENOPROTOOPT;
                        break;
                }
                break;

        case UDP_NO_CHECK6_TX:
                up->no_check6_tx = valbool;
                break;

        case UDP_NO_CHECK6_RX:
                up->no_check6_rx = valbool;
                break;

        case UDP_SEGMENT:
                if (val < 0 || val > USHRT_MAX)
                        return -EINVAL;
                up->gso_size = val;
                break;

        case UDP_GRO:
                lock_sock(sk);

                /* when enabling GRO, accept the related GSO packet type */
                if (valbool)
                        udp_tunnel_encap_enable(sk->sk_socket);
                up->gro_enabled = valbool;
                up->accept_udp_l4 = valbool;
                release_sock(sk);
                break;

        /*
         *      UDP-Lite's partial checksum coverage (RFC 3828).
         */
        /* The sender sets actual checksum coverage length via this option.
         * The case coverage > packet length is handled by send module. */
        case UDPLITE_SEND_CSCOV:
                if (!is_udplite)         /* Disable the option on UDP sockets */
                        return -ENOPROTOOPT;
                if (val != 0 && val < 8) /* Illegal coverage: use default (8) */
                        val = 8;
                else if (val > USHRT_MAX)
                        val = USHRT_MAX;
                up->pcslen = val;
                up->pcflag |= UDPLITE_SEND_CC;
                break;

        /* The receiver specifies a minimum checksum coverage value. To make
         * sense, this should be set to at least 8 (as done below). If zero is
         * used, this again means full checksum coverage.                     */
        case UDPLITE_RECV_CSCOV:
                if (!is_udplite)         /* Disable the option on UDP sockets */
                        return -ENOPROTOOPT;
                if (val != 0 && val < 8) /* Avoid silly minimal values.       */
                        val = 8;
                else if (val > USHRT_MAX)
                        val = USHRT_MAX;
                up->pcrlen = val;
                up->pcflag |= UDPLITE_RECV_CC;
                break;

        default:
                err = -ENOPROTOOPT;
                break;
        }

        return err;
}
EXPORT_SYMBOL(udp_lib_setsockopt);

int udp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
                   unsigned int optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_setsockopt(sk, level, optname,
                                          optval, optlen,
                                          udp_push_pending_frames);
        return ip_setsockopt(sk, level, optname, optval, optlen);
}

int udp_lib_getsockopt(struct sock *sk, int level, int optname,
                       char __user *optval, int __user *optlen)
{
        struct udp_sock *up = udp_sk(sk);
        int val, len;

        if (get_user(len, optlen))
                return -EFAULT;

        len = min_t(unsigned int, len, sizeof(int));

        if (len < 0)
                return -EINVAL;

        switch (optname) {
        case UDP_CORK:
                val = up->corkflag;
                break;

        case UDP_ENCAP:
                val = up->encap_type;
                break;

        case UDP_NO_CHECK6_TX:
                val = up->no_check6_tx;
                break;

        case UDP_NO_CHECK6_RX:
                val = up->no_check6_rx;
                break;

        case UDP_SEGMENT:
                val = up->gso_size;
                break;

        case UDP_GRO:
                val = up->gro_enabled;
                break;

        /* The following two cannot be changed on UDP sockets, the return is
         * always 0 (which corresponds to the full checksum coverage of UDP). */
        case UDPLITE_SEND_CSCOV:
                val = up->pcslen;
                break;

        case UDPLITE_RECV_CSCOV:
                val = up->pcrlen;
                break;

        default:
                return -ENOPROTOOPT;
        }

        if (put_user(len, optlen))
                return -EFAULT;
        if (copy_to_user(optval, &val, len))
                return -EFAULT;
        return 0;
}
EXPORT_SYMBOL(udp_lib_getsockopt);

int udp_getsockopt(struct sock *sk, int level, int optname,
                   char __user *optval, int __user *optlen)
{
        if (level == SOL_UDP  ||  level == SOL_UDPLITE)
                return udp_lib_getsockopt(sk, level, optname, optval, optlen);
        return ip_getsockopt(sk, level, optname, optval, optlen);
}

/**
 *      udp_poll - wait for a UDP event.
 *      @file: - file struct
 *      @sock: - socket
 *      @wait: - poll table
 *
 *      This is same as datagram poll, except for the special case of
 *      blocking sockets. If application is using a blocking fd
 *      and a packet with checksum error is in the queue;
 *      then it could get return from select indicating data available
 *      but then block when reading it. Add special case code
 *      to work around these arguably broken applications.
 */
__poll_t udp_poll(struct file *file, struct socket *sock, poll_table *wait)
{
        __poll_t mask = datagram_poll(file, sock, wait);
        struct sock *sk = sock->sk;

        if (!skb_queue_empty_lockless(&udp_sk(sk)->reader_queue))
                mask |= EPOLLIN | EPOLLRDNORM;

        /* Check for false positives due to checksum errors */
        if ((mask & EPOLLRDNORM) && !(file->f_flags & O_NONBLOCK) &&
            !(sk->sk_shutdown & RCV_SHUTDOWN) && first_packet_length(sk) == -1)
                mask &= ~(EPOLLIN | EPOLLRDNORM);

        return mask;

}
EXPORT_SYMBOL(udp_poll);

int udp_abort(struct sock *sk, int err)
{
        lock_sock(sk);

        sk->sk_err = err;
        sk->sk_error_report(sk);
        __udp_disconnect(sk, 0);

        release_sock(sk);

        return 0;
}
EXPORT_SYMBOL_GPL(udp_abort);

struct proto udp_prot = {
        .name                   = "UDP",
        .owner                  = THIS_MODULE,
        .close                  = udp_lib_close,
        .pre_connect            = udp_pre_connect,
        .connect                = ip4_datagram_connect,
        .disconnect             = udp_disconnect,
        .ioctl                  = udp_ioctl,
        .init                   = udp_init_sock,
        .destroy                = udp_destroy_sock,
        .setsockopt             = udp_setsockopt,
        .getsockopt             = udp_getsockopt,
        .sendmsg                = udp_sendmsg,
        .recvmsg                = udp_recvmsg,
        .sendpage               = udp_sendpage,
        .release_cb             = ip4_datagram_release_cb,
        .hash                   = udp_lib_hash,
        .unhash                 = udp_lib_unhash,
        .rehash                 = udp_v4_rehash,
        .get_port               = udp_v4_get_port,
#ifdef CONFIG_BPF_SYSCALL
        .psock_update_sk_prot   = udp_bpf_update_proto,
#endif
        .memory_allocated       = &udp_memory_allocated,
        .sysctl_mem             = sysctl_udp_mem,
        .sysctl_wmem_offset     = offsetof(struct net, ipv4.sysctl_udp_wmem_min),
        .sysctl_rmem_offset     = offsetof(struct net, ipv4.sysctl_udp_rmem_min),
        .obj_size               = sizeof(struct udp_sock),
        .h.udp_table            = &udp_table,
        .diag_destroy           = udp_abort,
};
EXPORT_SYMBOL(udp_prot);

/* ------------------------------------------------------------------------ */
#ifdef CONFIG_PROC_FS

static struct sock *udp_get_first(struct seq_file *seq, int start)
{
        struct sock *sk;
        struct udp_seq_afinfo *afinfo;
        struct udp_iter_state *state = seq->private;
        struct net *net = seq_file_net(seq);

        if (state->bpf_seq_afinfo)
                afinfo = state->bpf_seq_afinfo;
        else
                afinfo = PDE_DATA(file_inode(seq->file));

        for (state->bucket = start; state->bucket <= afinfo->udp_table->mask;
             ++state->bucket) {
                struct udp_hslot *hslot = &afinfo->udp_table->hash[state->bucket];

                if (hlist_empty(&hslot->head))
                        continue;

                spin_lock_bh(&hslot->lock);
                sk_for_each(sk, &hslot->head) {
                        if (!net_eq(sock_net(sk), net))
                                continue;
                        if (afinfo->family == AF_UNSPEC ||
                            sk->sk_family == afinfo->family)
                                goto found;
                }
                spin_unlock_bh(&hslot->lock);
        }
        sk = NULL;
found:
        return sk;
}

static struct sock *udp_get_next(struct seq_file *seq, struct sock *sk)
{
        struct udp_seq_afinfo *afinfo;
        struct udp_iter_state *state = seq->private;
        struct net *net = seq_file_net(seq);

        if (state->bpf_seq_afinfo)
                afinfo = state->bpf_seq_afinfo;
        else
                afinfo = PDE_DATA(file_inode(seq->file));

        do {
                sk = sk_next(sk);
        } while (sk && (!net_eq(sock_net(sk), net) ||
                        (afinfo->family != AF_UNSPEC &&
                         sk->sk_family != afinfo->family)));

        if (!sk) {
                if (state->bucket <= afinfo->udp_table->mask)
                        spin_unlock_bh(&afinfo->udp_table->hash[state->bucket].lock);
                return udp_get_first(seq, state->bucket + 1);
        }
        return sk;
}

static struct sock *udp_get_idx(struct seq_file *seq, loff_t pos)
{
        struct sock *sk = udp_get_first(seq, 0);

        if (sk)
                while (pos && (sk = udp_get_next(seq, sk)) != NULL)
                        --pos;
        return pos ? NULL : sk;
}

void *udp_seq_start(struct seq_file *seq, loff_t *pos)
{
        struct udp_iter_state *state = seq->private;
        state->bucket = MAX_UDP_PORTS;

        return *pos ? udp_get_idx(seq, *pos-1) : SEQ_START_TOKEN;
}
EXPORT_SYMBOL(udp_seq_start);

void *udp_seq_next(struct seq_file *seq, void *v, loff_t *pos)
{
        struct sock *sk;

        if (v == SEQ_START_TOKEN)
                sk = udp_get_idx(seq, 0);
        else
                sk = udp_get_next(seq, v);

        ++*pos;
        return sk;
}
EXPORT_SYMBOL(udp_seq_next);

void udp_seq_stop(struct seq_file *seq, void *v)
{
        struct udp_seq_afinfo *afinfo;
        struct udp_iter_state *state = seq->private;

        if (state->bpf_seq_afinfo)
                afinfo = state->bpf_seq_afinfo;
        else
                afinfo = PDE_DATA(file_inode(seq->file));

        if (state->bucket <= afinfo->udp_table->mask)
                spin_unlock_bh(&afinfo->udp_table->hash[state->bucket].lock);
}
EXPORT_SYMBOL(udp_seq_stop);

/* ------------------------------------------------------------------------ */
static void udp4_format_sock(struct sock *sp, struct seq_file *f,
                int bucket)
{
        struct inet_sock *inet = inet_sk(sp);
        __be32 dest = inet->inet_daddr;
        __be32 src  = inet->inet_rcv_saddr;
        __u16 destp       = ntohs(inet->inet_dport);
        __u16 srcp        = ntohs(inet->inet_sport);

        seq_printf(f, "%5d: %08X:%04X %08X:%04X"
                " %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %u",
                bucket, src, srcp, dest, destp, sp->sk_state,
                sk_wmem_alloc_get(sp),
                udp_rqueue_get(sp),
                0, 0L, 0,
                from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
                0, sock_i_ino(sp),
                refcount_read(&sp->sk_refcnt), sp,
                atomic_read(&sp->sk_drops));
}

int udp4_seq_show(struct seq_file *seq, void *v)
{
        seq_setwidth(seq, 127);
        if (v == SEQ_START_TOKEN)
                seq_puts(seq, "  sl  local_address rem_address   st tx_queue "
                           "rx_queue tr tm->when retrnsmt   uid  timeout "
                           "inode ref pointer drops");
        else {
                struct udp_iter_state *state = seq->private;

                udp4_format_sock(v, seq, state->bucket);
        }
        seq_pad(seq, '\n');
        return 0;
}

#ifdef CONFIG_BPF_SYSCALL
struct bpf_iter__udp {
        __bpf_md_ptr(struct bpf_iter_meta *, meta);
        __bpf_md_ptr(struct udp_sock *, udp_sk);
        uid_t uid __aligned(8);
        int bucket __aligned(8);
};

static int udp_prog_seq_show(struct bpf_prog *prog, struct bpf_iter_meta *meta,
                             struct udp_sock *udp_sk, uid_t uid, int bucket)
{
        struct bpf_iter__udp ctx;

        meta->seq_num--;  /* skip SEQ_START_TOKEN */
        ctx.meta = meta;
        ctx.udp_sk = udp_sk;
        ctx.uid = uid;
        ctx.bucket = bucket;
        return bpf_iter_run_prog(prog, &ctx);
}

static int bpf_iter_udp_seq_show(struct seq_file *seq, void *v)
{
        struct udp_iter_state *state = seq->private;
        struct bpf_iter_meta meta;
        struct bpf_prog *prog;
        struct sock *sk = v;
        uid_t uid;

        if (v == SEQ_START_TOKEN)
                return 0;

        uid = from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk));
        meta.seq = seq;
        prog = bpf_iter_get_info(&meta, false);
        return udp_prog_seq_show(prog, &meta, v, uid, state->bucket);
}

static void bpf_iter_udp_seq_stop(struct seq_file *seq, void *v)
{
        struct bpf_iter_meta meta;
        struct bpf_prog *prog;

        if (!v) {
                meta.seq = seq;
                prog = bpf_iter_get_info(&meta, true);
                if (prog)
                        (void)udp_prog_seq_show(prog, &meta, v, 0, 0);
        }

        udp_seq_stop(seq, v);
}

static const struct seq_operations bpf_iter_udp_seq_ops = {
        .start          = udp_seq_start,
        .next           = udp_seq_next,
        .stop           = bpf_iter_udp_seq_stop,
        .show           = bpf_iter_udp_seq_show,
};
#endif

const struct seq_operations udp_seq_ops = {
        .start          = udp_seq_start,
        .next           = udp_seq_next,
        .stop           = udp_seq_stop,
        .show           = udp4_seq_show,
};
EXPORT_SYMBOL(udp_seq_ops);

static struct udp_seq_afinfo udp4_seq_afinfo = {
        .family         = AF_INET,
        .udp_table      = &udp_table,
};

static int __net_init udp4_proc_init_net(struct net *net)
{
        if (!proc_create_net_data("udp", 0444, net->proc_net, &udp_seq_ops,
                        sizeof(struct udp_iter_state), &udp4_seq_afinfo))
                return -ENOMEM;
        return 0;
}

static void __net_exit udp4_proc_exit_net(struct net *net)
{
        remove_proc_entry("udp", net->proc_net);
}

static struct pernet_operations udp4_net_ops = {
        .init = udp4_proc_init_net,
        .exit = udp4_proc_exit_net,
};

int __init udp4_proc_init(void)
{
        return register_pernet_subsys(&udp4_net_ops);
}

void udp4_proc_exit(void)
{
        unregister_pernet_subsys(&udp4_net_ops);
}
#endif /* CONFIG_PROC_FS */

static __initdata unsigned long uhash_entries;
static int __init set_uhash_entries(char *str)
{
        ssize_t ret;

        if (!str)
                return 0;

        ret = kstrtoul(str, 0, &uhash_entries);
        if (ret)
                return 0;

        if (uhash_entries && uhash_entries < UDP_HTABLE_SIZE_MIN)
                uhash_entries = UDP_HTABLE_SIZE_MIN;
        return 1;
}
__setup("uhash_entries=", set_uhash_entries);

void __init udp_table_init(struct udp_table *table, const char *name)
{
        unsigned int i;

        table->hash = alloc_large_system_hash(name,
                                              2 * sizeof(struct udp_hslot),
                                              uhash_entries,
                                              21, /* one slot per 2 MB */
                                              0,
                                              &table->log,
                                              &table->mask,
                                              UDP_HTABLE_SIZE_MIN,
                                              64 * 1024);

        table->hash2 = table->hash + (table->mask + 1);
        for (i = 0; i <= table->mask; i++) {
                INIT_HLIST_HEAD(&table->hash[i].head);
                table->hash[i].count = 0;
                spin_lock_init(&table->hash[i].lock);
        }
        for (i = 0; i <= table->mask; i++) {
                INIT_HLIST_HEAD(&table->hash2[i].head);
                table->hash2[i].count = 0;
                spin_lock_init(&table->hash2[i].lock);
        }
}

u32 udp_flow_hashrnd(void)
{
        static u32 hashrnd __read_mostly;

        net_get_random_once(&hashrnd, sizeof(hashrnd));

        return hashrnd;
}
EXPORT_SYMBOL(udp_flow_hashrnd);

static void __udp_sysctl_init(struct net *net)
{
        net->ipv4.sysctl_udp_rmem_min = SK_MEM_QUANTUM;
        net->ipv4.sysctl_udp_wmem_min = SK_MEM_QUANTUM;

#ifdef CONFIG_NET_L3_MASTER_DEV
        net->ipv4.sysctl_udp_l3mdev_accept = 0;
#endif
}

static int __net_init udp_sysctl_init(struct net *net)
{
        __udp_sysctl_init(net);
        return 0;
}

static struct pernet_operations __net_initdata udp_sysctl_ops = {
        .init   = udp_sysctl_init,
};

#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
DEFINE_BPF_ITER_FUNC(udp, struct bpf_iter_meta *meta,
                     struct udp_sock *udp_sk, uid_t uid, int bucket)

static int bpf_iter_init_udp(void *priv_data, struct bpf_iter_aux_info *aux)
{
        struct udp_iter_state *st = priv_data;
        struct udp_seq_afinfo *afinfo;
        int ret;

        afinfo = kmalloc(sizeof(*afinfo), GFP_USER | __GFP_NOWARN);
        if (!afinfo)
                return -ENOMEM;

        afinfo->family = AF_UNSPEC;
        afinfo->udp_table = &udp_table;
        st->bpf_seq_afinfo = afinfo;
        ret = bpf_iter_init_seq_net(priv_data, aux);
        if (ret)
                kfree(afinfo);
        return ret;
}

static void bpf_iter_fini_udp(void *priv_data)
{
        struct udp_iter_state *st = priv_data;

        kfree(st->bpf_seq_afinfo);
        bpf_iter_fini_seq_net(priv_data);
}

static const struct bpf_iter_seq_info udp_seq_info = {
        .seq_ops                = &bpf_iter_udp_seq_ops,
        .init_seq_private       = bpf_iter_init_udp,
        .fini_seq_private       = bpf_iter_fini_udp,
        .seq_priv_size          = sizeof(struct udp_iter_state),
};

static struct bpf_iter_reg udp_reg_info = {
        .target                 = "udp",
        .ctx_arg_info_size      = 1,
        .ctx_arg_info           = {
                { offsetof(struct bpf_iter__udp, udp_sk),
                  PTR_TO_BTF_ID_OR_NULL },
        },
        .seq_info               = &udp_seq_info,
};

static void __init bpf_iter_register(void)
{
        udp_reg_info.ctx_arg_info[0].btf_id = btf_sock_ids[BTF_SOCK_TYPE_UDP];
        if (bpf_iter_reg_target(&udp_reg_info))
                pr_warn("Warning: could not register bpf iterator udp\n");
}
#endif

void __init udp_init(void)
{
        unsigned long limit;
        unsigned int i;

        udp_table_init(&udp_table, "UDP");
        limit = nr_free_buffer_pages() / 8;
        limit = max(limit, 128UL);
        sysctl_udp_mem[0] = limit / 4 * 3;
        sysctl_udp_mem[1] = limit;
        sysctl_udp_mem[2] = sysctl_udp_mem[0] * 2;

        __udp_sysctl_init(&init_net);

        /* 16 spinlocks per cpu */
        udp_busylocks_log = ilog2(nr_cpu_ids) + 4;
        udp_busylocks = kmalloc(sizeof(spinlock_t) << udp_busylocks_log,
                                GFP_KERNEL);
        if (!udp_busylocks)
                panic("UDP: failed to alloc udp_busylocks\n");
        for (i = 0; i < (1U << udp_busylocks_log); i++)
                spin_lock_init(udp_busylocks + i);

        if (register_pernet_subsys(&udp_sysctl_ops))
                panic("UDP: failed to init sysctl parameters.\n");

#if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
        bpf_iter_register();
#endif
}