net/bridge/netfilter/nft_reject_bridge.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2014 Pablo Neira Ayuso <pablo@netfilter.org>
   4  */
   5
   6 #include <linux/kernel.h>
   7 #include <linux/init.h>
   8 #include <linux/module.h>
   9 #include <linux/netlink.h>
  10 #include <linux/netfilter.h>
  11 #include <linux/netfilter/nf_tables.h>
  12 #include <net/netfilter/nf_tables.h>
  13 #include <net/netfilter/nft_reject.h>
  14 #include <net/netfilter/ipv4/nf_reject.h>
  15 #include <net/netfilter/ipv6/nf_reject.h>
  16 #include <linux/ip.h>
  17 #include <net/ip.h>
  18 #include <net/ip6_checksum.h>
  19 #include <linux/netfilter_bridge.h>
  20 #include <linux/netfilter_ipv6.h>
  21 #include "../br_private.h"
  22
  23 static void nft_reject_br_push_etherhdr(struct sk_buff *oldskb,
  24                                         struct sk_buff *nskb)
  25 {
  26         struct ethhdr *eth;
  27
  28         eth = skb_push(nskb, ETH_HLEN);
  29         skb_reset_mac_header(nskb);
  30         ether_addr_copy(eth->h_source, eth_hdr(oldskb)->h_dest);
  31         ether_addr_copy(eth->h_dest, eth_hdr(oldskb)->h_source);
  32         eth->h_proto = eth_hdr(oldskb)->h_proto;
  33         skb_pull(nskb, ETH_HLEN);
  34
  35         if (skb_vlan_tag_present(oldskb)) {
  36                 u16 vid = skb_vlan_tag_get(oldskb);
  37
  38                 __vlan_hwaccel_put_tag(nskb, oldskb->vlan_proto, vid);
  39         }
  40 }
  41
  42 static int nft_bridge_iphdr_validate(struct sk_buff *skb)
  43 {
  44         struct iphdr *iph;
  45         u32 len;
  46
  47         if (!pskb_may_pull(skb, sizeof(struct iphdr)))
  48                 return 0;
  49
  50         iph = ip_hdr(skb);
  51         if (iph->ihl < 5 || iph->version != 4)
  52                 return 0;
  53
  54         len = ntohs(iph->tot_len);
  55         if (skb->len < len)
  56                 return 0;
  57         else if (len < (iph->ihl*4))
  58                 return 0;
  59
  60         if (!pskb_may_pull(skb, iph->ihl*4))
  61                 return 0;
  62
  63         return 1;
  64 }
  65
  66 /* We cannot use oldskb->dev, it can be either bridge device (NF_BRIDGE INPUT)
  67  * or the bridge port (NF_BRIDGE PREROUTING).
  68  */
  69 static void nft_reject_br_send_v4_tcp_reset(struct net *net,
  70                                             struct sk_buff *oldskb,
  71                                             const struct net_device *dev,
  72                                             int hook)
  73 {
  74         struct sk_buff *nskb;
  75         struct iphdr *niph;
  76         const struct tcphdr *oth;
  77         struct tcphdr _oth;
  78
  79         if (!nft_bridge_iphdr_validate(oldskb))
  80                 return;
  81
  82         oth = nf_reject_ip_tcphdr_get(oldskb, &_oth, hook);
  83         if (!oth)
  84                 return;
  85
  86         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct tcphdr) +
  87                          LL_MAX_HEADER, GFP_ATOMIC);
  88         if (!nskb)
  89                 return;
  90
  91         skb_reserve(nskb, LL_MAX_HEADER);
  92         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_TCP,
  93                                    net->ipv4.sysctl_ip_default_ttl);
  94         nf_reject_ip_tcphdr_put(nskb, oldskb, oth);
  95         niph->tot_len = htons(nskb->len);
  96         ip_send_check(niph);
  97
  98         nft_reject_br_push_etherhdr(oldskb, nskb);
  99
 100         br_forward(br_port_get_rcu(dev), nskb, false, true);
 101 }
 102
 103 static void nft_reject_br_send_v4_unreach(struct net *net,
 104                                           struct sk_buff *oldskb,
 105                                           const struct net_device *dev,
 106                                           int hook, u8 code)
 107 {
 108         struct sk_buff *nskb;
 109         struct iphdr *niph;
 110         struct icmphdr *icmph;
 111         unsigned int len;
 112         __wsum csum;
 113         u8 proto;
 114
 115         if (!nft_bridge_iphdr_validate(oldskb))
 116                 return;
 117
 118         /* IP header checks: fragment. */
 119         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
 120                 return;
 121
 122         /* RFC says return as much as we can without exceeding 576 bytes. */
 123         len = min_t(unsigned int, 536, oldskb->len);
 124
 125         if (!pskb_may_pull(oldskb, len))
 126                 return;
 127
 128         if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
 129                 return;
 130
 131         proto = ip_hdr(oldskb)->protocol;
 132
 133         if (!skb_csum_unnecessary(oldskb) &&
 134             nf_reject_verify_csum(proto) &&
 135             nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
 136                 return;
 137
 138         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
 139                          LL_MAX_HEADER + len, GFP_ATOMIC);
 140         if (!nskb)
 141                 return;
 142
 143         skb_reserve(nskb, LL_MAX_HEADER);
 144         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
 145                                    net->ipv4.sysctl_ip_default_ttl);
 146
 147         skb_reset_transport_header(nskb);
 148         icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
 149         icmph->type     = ICMP_DEST_UNREACH;
 150         icmph->code     = code;
 151
 152         skb_put_data(nskb, skb_network_header(oldskb), len);
 153
 154         csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
 155         icmph->checksum = csum_fold(csum);
 156
 157         niph->tot_len   = htons(nskb->len);
 158         ip_send_check(niph);
 159
 160         nft_reject_br_push_etherhdr(oldskb, nskb);
 161
 162         br_forward(br_port_get_rcu(dev), nskb, false, true);
 163 }
 164
 165 static int nft_bridge_ip6hdr_validate(struct sk_buff *skb)
 166 {
 167         struct ipv6hdr *hdr;
 168         u32 pkt_len;
 169
 170         if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 171                 return 0;
 172
 173         hdr = ipv6_hdr(skb);
 174         if (hdr->version != 6)
 175                 return 0;
 176
 177         pkt_len = ntohs(hdr->payload_len);
 178         if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
 179                 return 0;
 180
 181         return 1;
 182 }
 183
 184 static void nft_reject_br_send_v6_tcp_reset(struct net *net,
 185                                             struct sk_buff *oldskb,
 186                                             const struct net_device *dev,
 187                                             int hook)
 188 {
 189         struct sk_buff *nskb;
 190         const struct tcphdr *oth;
 191         struct tcphdr _oth;
 192         unsigned int otcplen;
 193         struct ipv6hdr *nip6h;
 194
 195         if (!nft_bridge_ip6hdr_validate(oldskb))
 196                 return;
 197
 198         oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
 199         if (!oth)
 200                 return;
 201
 202         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
 203                          LL_MAX_HEADER, GFP_ATOMIC);
 204         if (!nskb)
 205                 return;
 206
 207         skb_reserve(nskb, LL_MAX_HEADER);
 208         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
 209                                      net->ipv6.devconf_all->hop_limit);
 210         nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
 211         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 212
 213         nft_reject_br_push_etherhdr(oldskb, nskb);
 214
 215         br_forward(br_port_get_rcu(dev), nskb, false, true);
 216 }
 217
 218 static bool reject6_br_csum_ok(struct sk_buff *skb, int hook)
 219 {
 220         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 221         int thoff;
 222         __be16 fo;
 223         u8 proto = ip6h->nexthdr;
 224
 225         if (skb_csum_unnecessary(skb))
 226                 return true;
 227
 228         if (ip6h->payload_len &&
 229             pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
 230                 return false;
 231
 232         ip6h = ipv6_hdr(skb);
 233         thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
 234         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 235                 return false;
 236
 237         if (!nf_reject_verify_csum(proto))
 238                 return true;
 239
 240         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
 241 }
 242
 243 static void nft_reject_br_send_v6_unreach(struct net *net,
 244                                           struct sk_buff *oldskb,
 245                                           const struct net_device *dev,
 246                                           int hook, u8 code)
 247 {
 248         struct sk_buff *nskb;
 249         struct ipv6hdr *nip6h;
 250         struct icmp6hdr *icmp6h;
 251         unsigned int len;
 252
 253         if (!nft_bridge_ip6hdr_validate(oldskb))
 254                 return;
 255
 256         /* Include "As much of invoking packet as possible without the ICMPv6
 257          * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
 258          */
 259         len = min_t(unsigned int, 1220, oldskb->len);
 260
 261         if (!pskb_may_pull(oldskb, len))
 262                 return;
 263
 264         if (!reject6_br_csum_ok(oldskb, hook))
 265                 return;
 266
 267         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
 268                          LL_MAX_HEADER + len, GFP_ATOMIC);
 269         if (!nskb)
 270                 return;
 271
 272         skb_reserve(nskb, LL_MAX_HEADER);
 273         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
 274                                      net->ipv6.devconf_all->hop_limit);
 275
 276         skb_reset_transport_header(nskb);
 277         icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
 278         icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
 279         icmp6h->icmp6_code = code;
 280
 281         skb_put_data(nskb, skb_network_header(oldskb), len);
 282         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 283
 284         icmp6h->icmp6_cksum =
 285                 csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
 286                                 nskb->len - sizeof(struct ipv6hdr),
 287                                 IPPROTO_ICMPV6,
 288                                 csum_partial(icmp6h,
 289                                              nskb->len - sizeof(struct ipv6hdr),
 290                                              0));
 291
 292         nft_reject_br_push_etherhdr(oldskb, nskb);
 293
 294         br_forward(br_port_get_rcu(dev), nskb, false, true);
 295 }
 296
 297 static void nft_reject_bridge_eval(const struct nft_expr *expr,
 298                                    struct nft_regs *regs,
 299                                    const struct nft_pktinfo *pkt)
 300 {
 301         struct nft_reject *priv = nft_expr_priv(expr);
 302         const unsigned char *dest = eth_hdr(pkt->skb)->h_dest;
 303
 304         if (is_broadcast_ether_addr(dest) ||
 305             is_multicast_ether_addr(dest))
 306                 goto out;
 307
 308         switch (eth_hdr(pkt->skb)->h_proto) {
 309         case htons(ETH_P_IP):
 310                 switch (priv->type) {
 311                 case NFT_REJECT_ICMP_UNREACH:
 312                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 313                                                       nft_in(pkt),
 314                                                       nft_hook(pkt),
 315                                                       priv->icmp_code);
 316                         break;
 317                 case NFT_REJECT_TCP_RST:
 318                         nft_reject_br_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
 319                                                         nft_in(pkt),
 320                                                         nft_hook(pkt));
 321                         break;
 322                 case NFT_REJECT_ICMPX_UNREACH:
 323                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 324                                                       nft_in(pkt),
 325                                                       nft_hook(pkt),
 326                                                       nft_reject_icmp_code(priv->icmp_code));
 327                         break;
 328                 }
 329                 break;
 330         case htons(ETH_P_IPV6):
 331                 switch (priv->type) {
 332                 case NFT_REJECT_ICMP_UNREACH:
 333                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 334                                                       nft_in(pkt),
 335                                                       nft_hook(pkt),
 336                                                       priv->icmp_code);
 337                         break;
 338                 case NFT_REJECT_TCP_RST:
 339                         nft_reject_br_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
 340                                                         nft_in(pkt),
 341                                                         nft_hook(pkt));
 342                         break;
 343                 case NFT_REJECT_ICMPX_UNREACH:
 344                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 345                                                       nft_in(pkt),
 346                                                       nft_hook(pkt),
 347                                                       nft_reject_icmpv6_code(priv->icmp_code));
 348                         break;
 349                 }
 350                 break;
 351         default:
 352                 /* No explicit way to reject this protocol, drop it. */
 353                 break;
 354         }
 355 out:
 356         regs->verdict.code = NF_DROP;
 357 }
 358
 359 static int nft_reject_bridge_validate(const struct nft_ctx *ctx,
 360                                       const struct nft_expr *expr,
 361                                       const struct nft_data **data)
 362 {
 363         return nft_chain_validate_hooks(ctx->chain, (1 << NF_BR_PRE_ROUTING) |
 364                                                     (1 << NF_BR_LOCAL_IN));
 365 }
 366
 367 static int nft_reject_bridge_init(const struct nft_ctx *ctx,
 368                                   const struct nft_expr *expr,
 369                                   const struct nlattr * const tb[])
 370 {
 371         struct nft_reject *priv = nft_expr_priv(expr);
 372         int icmp_code;
 373
 374         if (tb[NFTA_REJECT_TYPE] == NULL)
 375                 return -EINVAL;
 376
 377         priv->type = ntohl(nla_get_be32(tb[NFTA_REJECT_TYPE]));
 378         switch (priv->type) {
 379         case NFT_REJECT_ICMP_UNREACH:
 380         case NFT_REJECT_ICMPX_UNREACH:
 381                 if (tb[NFTA_REJECT_ICMP_CODE] == NULL)
 382                         return -EINVAL;
 383
 384                 icmp_code = nla_get_u8(tb[NFTA_REJECT_ICMP_CODE]);
 385                 if (priv->type == NFT_REJECT_ICMPX_UNREACH &&
 386                     icmp_code > NFT_REJECT_ICMPX_MAX)
 387                         return -EINVAL;
 388
 389                 priv->icmp_code = icmp_code;
 390                 break;
 391         case NFT_REJECT_TCP_RST:
 392                 break;
 393         default:
 394                 return -EINVAL;
 395         }
 396         return 0;
 397 }
 398
 399 static int nft_reject_bridge_dump(struct sk_buff *skb,
 400                                   const struct nft_expr *expr)
 401 {
 402         const struct nft_reject *priv = nft_expr_priv(expr);
 403
 404         if (nla_put_be32(skb, NFTA_REJECT_TYPE, htonl(priv->type)))
 405                 goto nla_put_failure;
 406
 407         switch (priv->type) {
 408         case NFT_REJECT_ICMP_UNREACH:
 409         case NFT_REJECT_ICMPX_UNREACH:
 410                 if (nla_put_u8(skb, NFTA_REJECT_ICMP_CODE, priv->icmp_code))
 411                         goto nla_put_failure;
 412                 break;
 413         default:
 414                 break;
 415         }
 416
 417         return 0;
 418
 419 nla_put_failure:
 420         return -1;
 421 }
 422
 423 static struct nft_expr_type nft_reject_bridge_type;
 424 static const struct nft_expr_ops nft_reject_bridge_ops = {
 425         .type           = &nft_reject_bridge_type,
 426         .size           = NFT_EXPR_SIZE(sizeof(struct nft_reject)),
 427         .eval           = nft_reject_bridge_eval,
 428         .init           = nft_reject_bridge_init,
 429         .dump           = nft_reject_bridge_dump,
 430         .validate       = nft_reject_bridge_validate,
 431 };
 432
 433 static struct nft_expr_type nft_reject_bridge_type __read_mostly = {
 434         .family         = NFPROTO_BRIDGE,
 435         .name           = "reject",
 436         .ops            = &nft_reject_bridge_ops,
 437         .policy         = nft_reject_policy,
 438         .maxattr        = NFTA_REJECT_MAX,
 439         .owner          = THIS_MODULE,
 440 };
 441
 442 static int __init nft_reject_bridge_module_init(void)
 443 {
 444         return nft_register_expr(&nft_reject_bridge_type);
 445 }
 446
 447 static void __exit nft_reject_bridge_module_exit(void)
 448 {
 449         nft_unregister_expr(&nft_reject_bridge_type);
 450 }
 451
 452 module_init(nft_reject_bridge_module_init);
 453 module_exit(nft_reject_bridge_module_exit);
 454
 455 MODULE_LICENSE("GPL");
 456 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
 457 MODULE_ALIAS_NFT_AF_EXPR(AF_BRIDGE, "reject");
 458 MODULE_DESCRIPTION("Reject packets from bridge via nftables");