net/bridge/netfilter/nft_reject_bridge.c

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