tcp: Fix data-races around sysctl_tcp_syncookies.

While reading sysctl_tcp_syncookies, it can be changed concurrently.
Thus, we need to add READ_ONCE() to its readers.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/core/filter.c b/net/core/filter.c
index 2a6a0b0..7950f75 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -7041,7 +7041,7 @@ BPF_CALL_5(bpf_tcp_check_syncookie, struct sock *, sk, void *, iph, u32, iph_len
        if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
                return -EINVAL;
 
-       if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+       if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
                return -EINVAL;
 
        if (!th->ack || th->rst || th->syn)
@@ -7116,7 +7116,7 @@ BPF_CALL_5(bpf_tcp_gen_syncookie, struct sock *, sk, void *, iph, u32, iph_len,
        if (sk->sk_protocol != IPPROTO_TCP || sk->sk_state != TCP_LISTEN)
                return -EINVAL;
 
-       if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies)
+       if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies))
                return -ENOENT;
 
        if (!th->syn || th->ack || th->fin || th->rst)

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index b387c48..9b234b4 100644 (file)
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -340,7 +340,8 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb)
        struct flowi4 fl4;
        u32 tsoff = 0;
 
-       if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+       if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+           !th->ack || th->rst)
                goto out;
 
        if (tcp_synq_no_recent_overflow(sk))

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3ec4edc..8271eaa 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6797,11 +6797,14 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 {
        struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
        const char *msg = "Dropping request";
-       bool want_cookie = false;
        struct net *net = sock_net(sk);
+       bool want_cookie = false;
+       u8 syncookies;
+
+       syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
 
 #ifdef CONFIG_SYN_COOKIES
-       if (net->ipv4.sysctl_tcp_syncookies) {
+       if (syncookies) {
                msg = "Sending cookies";
                want_cookie = true;
                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
@@ -6809,8 +6812,7 @@ static bool tcp_syn_flood_action(const struct sock *sk, const char *proto)
 #endif
                __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
 
-       if (!queue->synflood_warned &&
-           net->ipv4.sysctl_tcp_syncookies != 2 &&
+       if (!queue->synflood_warned && syncookies != 2 &&
            xchg(&queue->synflood_warned, 1) == 0)
                net_info_ratelimited("%s: Possible SYN flooding on port %d. %s.  Check SNMP counters.\n",
                                     proto, sk->sk_num, msg);
@@ -6859,7 +6861,7 @@ u16 tcp_get_syncookie_mss(struct request_sock_ops *rsk_ops,
        struct tcp_sock *tp = tcp_sk(sk);
        u16 mss;
 
-       if (sock_net(sk)->ipv4.sysctl_tcp_syncookies != 2 &&
+       if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) != 2 &&
            !inet_csk_reqsk_queue_is_full(sk))
                return 0;
 
@@ -6893,13 +6895,15 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
        bool want_cookie = false;
        struct dst_entry *dst;
        struct flowi fl;
+       u8 syncookies;
+
+       syncookies = READ_ONCE(net->ipv4.sysctl_tcp_syncookies);
 
        /* TW buckets are converted to open requests without
         * limitations, they conserve resources and peer is
         * evidently real one.
         */
-       if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
-            inet_csk_reqsk_queue_is_full(sk)) && !isn) {
+       if ((syncookies == 2 || inet_csk_reqsk_queue_is_full(sk)) && !isn) {
                want_cookie = tcp_syn_flood_action(sk, rsk_ops->slab_name);
                if (!want_cookie)
                        goto drop;
@@ -6949,7 +6953,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 
        if (!want_cookie && !isn) {
                /* Kill the following clause, if you dislike this way. */
-               if (!net->ipv4.sysctl_tcp_syncookies &&
+               if (!syncookies &&
                    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
                     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
                    !tcp_peer_is_proven(req, dst)) {

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 9cc123f..5014aa6 100644 (file)
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -141,7 +141,8 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
        __u8 rcv_wscale;
        u32 tsoff = 0;
 
-       if (!sock_net(sk)->ipv4.sysctl_tcp_syncookies || !th->ack || th->rst)
+       if (!READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syncookies) ||
+           !th->ack || th->rst)
                goto out;
 
        if (tcp_synq_no_recent_overflow(sk))