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 = (struct ethhdr *)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         void *payload;
 111         __wsum csum;
 112         u8 proto;
 113
 114         if (!nft_bridge_iphdr_validate(oldskb))
 115                 return;
 116
 117         /* IP header checks: fragment. */
 118         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
 119                 return;
 120
 121         /* RFC says return as much as we can without exceeding 576 bytes. */
 122         len = min_t(unsigned int, 536, oldskb->len);
 123
 124         if (!pskb_may_pull(oldskb, len))
 125                 return;
 126
 127         if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
 128                 return;
 129
 130         if (ip_hdr(oldskb)->protocol == IPPROTO_TCP ||
 131             ip_hdr(oldskb)->protocol == IPPROTO_UDP)
 132                 proto = ip_hdr(oldskb)->protocol;
 133         else
 134                 proto = 0;
 135
 136         if (!skb_csum_unnecessary(oldskb) &&
 137             nf_ip_checksum(oldskb, hook, ip_hdrlen(oldskb), proto))
 138                 return;
 139
 140         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmphdr) +
 141                          LL_MAX_HEADER + len, GFP_ATOMIC);
 142         if (!nskb)
 143                 return;
 144
 145         skb_reserve(nskb, LL_MAX_HEADER);
 146         niph = nf_reject_iphdr_put(nskb, oldskb, IPPROTO_ICMP,
 147                                    net->ipv4.sysctl_ip_default_ttl);
 148
 149         skb_reset_transport_header(nskb);
 150         icmph = skb_put_zero(nskb, sizeof(struct icmphdr));
 151         icmph->type     = ICMP_DEST_UNREACH;
 152         icmph->code     = code;
 153
 154         payload = skb_put_data(nskb, skb_network_header(oldskb), len);
 155
 156         csum = csum_partial((void *)icmph, len + sizeof(struct icmphdr), 0);
 157         icmph->checksum = csum_fold(csum);
 158
 159         niph->tot_len   = htons(nskb->len);
 160         ip_send_check(niph);
 161
 162         nft_reject_br_push_etherhdr(oldskb, nskb);
 163
 164         br_forward(br_port_get_rcu(dev), nskb, false, true);
 165 }
 166
 167 static int nft_bridge_ip6hdr_validate(struct sk_buff *skb)
 168 {
 169         struct ipv6hdr *hdr;
 170         u32 pkt_len;
 171
 172         if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 173                 return 0;
 174
 175         hdr = ipv6_hdr(skb);
 176         if (hdr->version != 6)
 177                 return 0;
 178
 179         pkt_len = ntohs(hdr->payload_len);
 180         if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
 181                 return 0;
 182
 183         return 1;
 184 }
 185
 186 static void nft_reject_br_send_v6_tcp_reset(struct net *net,
 187                                             struct sk_buff *oldskb,
 188                                             const struct net_device *dev,
 189                                             int hook)
 190 {
 191         struct sk_buff *nskb;
 192         const struct tcphdr *oth;
 193         struct tcphdr _oth;
 194         unsigned int otcplen;
 195         struct ipv6hdr *nip6h;
 196
 197         if (!nft_bridge_ip6hdr_validate(oldskb))
 198                 return;
 199
 200         oth = nf_reject_ip6_tcphdr_get(oldskb, &_oth, &otcplen, hook);
 201         if (!oth)
 202                 return;
 203
 204         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct tcphdr) +
 205                          LL_MAX_HEADER, GFP_ATOMIC);
 206         if (!nskb)
 207                 return;
 208
 209         skb_reserve(nskb, LL_MAX_HEADER);
 210         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_TCP,
 211                                      net->ipv6.devconf_all->hop_limit);
 212         nf_reject_ip6_tcphdr_put(nskb, oldskb, oth, otcplen);
 213         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 214
 215         nft_reject_br_push_etherhdr(oldskb, nskb);
 216
 217         br_forward(br_port_get_rcu(dev), nskb, false, true);
 218 }
 219
 220 static bool reject6_br_csum_ok(struct sk_buff *skb, int hook)
 221 {
 222         const struct ipv6hdr *ip6h = ipv6_hdr(skb);
 223         int thoff;
 224         __be16 fo;
 225         u8 proto = ip6h->nexthdr;
 226
 227         if (skb_csum_unnecessary(skb))
 228                 return true;
 229
 230         if (ip6h->payload_len &&
 231             pskb_trim_rcsum(skb, ntohs(ip6h->payload_len) + sizeof(*ip6h)))
 232                 return false;
 233
 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         void *payload;
 251
 252         if (!nft_bridge_ip6hdr_validate(oldskb))
 253                 return;
 254
 255         /* Include "As much of invoking packet as possible without the ICMPv6
 256          * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
 257          */
 258         len = min_t(unsigned int, 1220, oldskb->len);
 259
 260         if (!pskb_may_pull(oldskb, len))
 261                 return;
 262
 263         if (!reject6_br_csum_ok(oldskb, hook))
 264                 return;
 265
 266         nskb = alloc_skb(sizeof(struct iphdr) + sizeof(struct icmp6hdr) +
 267                          LL_MAX_HEADER + len, GFP_ATOMIC);
 268         if (!nskb)
 269                 return;
 270
 271         skb_reserve(nskb, LL_MAX_HEADER);
 272         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
 273                                      net->ipv6.devconf_all->hop_limit);
 274
 275         skb_reset_transport_header(nskb);
 276         icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
 277         icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
 278         icmp6h->icmp6_code = code;
 279
 280         payload = skb_put_data(nskb, skb_network_header(oldskb), len);
 281         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 282
 283         icmp6h->icmp6_cksum =
 284                 csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
 285                                 nskb->len - sizeof(struct ipv6hdr),
 286                                 IPPROTO_ICMPV6,
 287                                 csum_partial(icmp6h,
 288                                              nskb->len - sizeof(struct ipv6hdr),
 289                                              0));
 290
 291         nft_reject_br_push_etherhdr(oldskb, nskb);
 292
 293         br_forward(br_port_get_rcu(dev), nskb, false, true);
 294 }
 295
 296 static void nft_reject_bridge_eval(const struct nft_expr *expr,
 297                                    struct nft_regs *regs,
 298                                    const struct nft_pktinfo *pkt)
 299 {
 300         struct nft_reject *priv = nft_expr_priv(expr);
 301         const unsigned char *dest = eth_hdr(pkt->skb)->h_dest;
 302
 303         if (is_broadcast_ether_addr(dest) ||
 304             is_multicast_ether_addr(dest))
 305                 goto out;
 306
 307         switch (eth_hdr(pkt->skb)->h_proto) {
 308         case htons(ETH_P_IP):
 309                 switch (priv->type) {
 310                 case NFT_REJECT_ICMP_UNREACH:
 311                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 312                                                       nft_in(pkt),
 313                                                       nft_hook(pkt),
 314                                                       priv->icmp_code);
 315                         break;
 316                 case NFT_REJECT_TCP_RST:
 317                         nft_reject_br_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
 318                                                         nft_in(pkt),
 319                                                         nft_hook(pkt));
 320                         break;
 321                 case NFT_REJECT_ICMPX_UNREACH:
 322                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 323                                                       nft_in(pkt),
 324                                                       nft_hook(pkt),
 325                                                       nft_reject_icmp_code(priv->icmp_code));
 326                         break;
 327                 }
 328                 break;
 329         case htons(ETH_P_IPV6):
 330                 switch (priv->type) {
 331                 case NFT_REJECT_ICMP_UNREACH:
 332                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 333                                                       nft_in(pkt),
 334                                                       nft_hook(pkt),
 335                                                       priv->icmp_code);
 336                         break;
 337                 case NFT_REJECT_TCP_RST:
 338                         nft_reject_br_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
 339                                                         nft_in(pkt),
 340                                                         nft_hook(pkt));
 341                         break;
 342                 case NFT_REJECT_ICMPX_UNREACH:
 343                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 344                                                       nft_in(pkt),
 345                                                       nft_hook(pkt),
 346                                                       nft_reject_icmpv6_code(priv->icmp_code));
 347                         break;
 348                 }
 349                 break;
 350         default:
 351                 /* No explicit way to reject this protocol, drop it. */
 352                 break;
 353         }
 354 out:
 355         regs->verdict.code = NF_DROP;
 356 }
 357
 358 static int nft_reject_bridge_validate(const struct nft_ctx *ctx,
 359                                       const struct nft_expr *expr,
 360                                       const struct nft_data **data)
 361 {
 362         return nft_chain_validate_hooks(ctx->chain, (1 << NF_BR_PRE_ROUTING) |
 363                                                     (1 << NF_BR_LOCAL_IN));
 364 }
 365
 366 static int nft_reject_bridge_init(const struct nft_ctx *ctx,
 367                                   const struct nft_expr *expr,
 368                                   const struct nlattr * const tb[])
 369 {
 370         struct nft_reject *priv = nft_expr_priv(expr);
 371         int icmp_code;
 372
 373         if (tb[NFTA_REJECT_TYPE] == NULL)
 374                 return -EINVAL;
 375
 376         priv->type = ntohl(nla_get_be32(tb[NFTA_REJECT_TYPE]));
 377         switch (priv->type) {
 378         case NFT_REJECT_ICMP_UNREACH:
 379         case NFT_REJECT_ICMPX_UNREACH:
 380                 if (tb[NFTA_REJECT_ICMP_CODE] == NULL)
 381                         return -EINVAL;
 382
 383                 icmp_code = nla_get_u8(tb[NFTA_REJECT_ICMP_CODE]);
 384                 if (priv->type == NFT_REJECT_ICMPX_UNREACH &&
 385                     icmp_code > NFT_REJECT_ICMPX_MAX)
 386                         return -EINVAL;
 387
 388                 priv->icmp_code = icmp_code;
 389                 break;
 390         case NFT_REJECT_TCP_RST:
 391                 break;
 392         default:
 393                 return -EINVAL;
 394         }
 395         return 0;
 396 }
 397
 398 static int nft_reject_bridge_dump(struct sk_buff *skb,
 399                                   const struct nft_expr *expr)
 400 {
 401         const struct nft_reject *priv = nft_expr_priv(expr);
 402
 403         if (nla_put_be32(skb, NFTA_REJECT_TYPE, htonl(priv->type)))
 404                 goto nla_put_failure;
 405
 406         switch (priv->type) {
 407         case NFT_REJECT_ICMP_UNREACH:
 408         case NFT_REJECT_ICMPX_UNREACH:
 409                 if (nla_put_u8(skb, NFTA_REJECT_ICMP_CODE, priv->icmp_code))
 410                         goto nla_put_failure;
 411                 break;
 412         default:
 413                 break;
 414         }
 415
 416         return 0;
 417
 418 nla_put_failure:
 419         return -1;
 420 }
 421
 422 static struct nft_expr_type nft_reject_bridge_type;
 423 static const struct nft_expr_ops nft_reject_bridge_ops = {
 424         .type           = &nft_reject_bridge_type,
 425         .size           = NFT_EXPR_SIZE(sizeof(struct nft_reject)),
 426         .eval           = nft_reject_bridge_eval,
 427         .init           = nft_reject_bridge_init,
 428         .dump           = nft_reject_bridge_dump,
 429         .validate       = nft_reject_bridge_validate,
 430 };
 431
 432 static struct nft_expr_type nft_reject_bridge_type __read_mostly = {
 433         .family         = NFPROTO_BRIDGE,
 434         .name           = "reject",
 435         .ops            = &nft_reject_bridge_ops,
 436         .policy         = nft_reject_policy,
 437         .maxattr        = NFTA_REJECT_MAX,
 438         .owner          = THIS_MODULE,
 439 };
 440
 441 static int __init nft_reject_bridge_module_init(void)
 442 {
 443         return nft_register_expr(&nft_reject_bridge_type);
 444 }
 445
 446 static void __exit nft_reject_bridge_module_exit(void)
 447 {
 448         nft_unregister_expr(&nft_reject_bridge_type);
 449 }
 450
 451 module_init(nft_reject_bridge_module_init);
 452 module_exit(nft_reject_bridge_module_exit);
 453
 454 MODULE_LICENSE("GPL");
 455 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
 456 MODULE_ALIAS_NFT_AF_EXPR(AF_BRIDGE, "reject");