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->tot_len = htons(nskb->len);
  93         ip_send_check(niph);
  94
  95         nft_reject_br_push_etherhdr(oldskb, nskb);
  96
  97         br_forward(br_port_get_rcu(dev), nskb, false, true);
  98 }
  99
 100 static void nft_reject_br_send_v4_unreach(struct net *net,
 101                                           struct sk_buff *oldskb,
 102                                           const struct net_device *dev,
 103                                           int hook, u8 code)
 104 {
 105         struct sk_buff *nskb;
 106         struct iphdr *niph;
 107         struct icmphdr *icmph;
 108         unsigned int len;
 109         __wsum csum;
 110         u8 proto;
 111
 112         if (!nft_bridge_iphdr_validate(oldskb))
 113                 return;
 114
 115         /* IP header checks: fragment. */
 116         if (ip_hdr(oldskb)->frag_off & htons(IP_OFFSET))
 117                 return;
 118
 119         /* RFC says return as much as we can without exceeding 576 bytes. */
 120         len = min_t(unsigned int, 536, oldskb->len);
 121
 122         if (!pskb_may_pull(oldskb, len))
 123                 return;
 124
 125         if (pskb_trim_rcsum(oldskb, ntohs(ip_hdr(oldskb)->tot_len)))
 126                 return;
 127
 128         if (ip_hdr(oldskb)->protocol == IPPROTO_TCP ||
 129             ip_hdr(oldskb)->protocol == IPPROTO_UDP)
 130                 proto = ip_hdr(oldskb)->protocol;
 131         else
 132                 proto = 0;
 133
 134         if (!skb_csum_unnecessary(oldskb) &&
 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         thoff = ipv6_skip_exthdr(skb, ((u8*)(ip6h+1) - skb->data), &proto, &fo);
 233         if (thoff < 0 || thoff >= skb->len || (fo & htons(~0x7)) != 0)
 234                 return false;
 235
 236         return nf_ip6_checksum(skb, hook, thoff, proto) == 0;
 237 }
 238
 239 static void nft_reject_br_send_v6_unreach(struct net *net,
 240                                           struct sk_buff *oldskb,
 241                                           const struct net_device *dev,
 242                                           int hook, u8 code)
 243 {
 244         struct sk_buff *nskb;
 245         struct ipv6hdr *nip6h;
 246         struct icmp6hdr *icmp6h;
 247         unsigned int len;
 248
 249         if (!nft_bridge_ip6hdr_validate(oldskb))
 250                 return;
 251
 252         /* Include "As much of invoking packet as possible without the ICMPv6
 253          * packet exceeding the minimum IPv6 MTU" in the ICMP payload.
 254          */
 255         len = min_t(unsigned int, 1220, oldskb->len);
 256
 257         if (!pskb_may_pull(oldskb, len))
 258                 return;
 259
 260         if (!reject6_br_csum_ok(oldskb, hook))
 261                 return;
 262
 263         nskb = alloc_skb(sizeof(struct ipv6hdr) + sizeof(struct icmp6hdr) +
 264                          LL_MAX_HEADER + len, GFP_ATOMIC);
 265         if (!nskb)
 266                 return;
 267
 268         skb_reserve(nskb, LL_MAX_HEADER);
 269         nip6h = nf_reject_ip6hdr_put(nskb, oldskb, IPPROTO_ICMPV6,
 270                                      net->ipv6.devconf_all->hop_limit);
 271
 272         skb_reset_transport_header(nskb);
 273         icmp6h = skb_put_zero(nskb, sizeof(struct icmp6hdr));
 274         icmp6h->icmp6_type = ICMPV6_DEST_UNREACH;
 275         icmp6h->icmp6_code = code;
 276
 277         skb_put_data(nskb, skb_network_header(oldskb), len);
 278         nip6h->payload_len = htons(nskb->len - sizeof(struct ipv6hdr));
 279
 280         icmp6h->icmp6_cksum =
 281                 csum_ipv6_magic(&nip6h->saddr, &nip6h->daddr,
 282                                 nskb->len - sizeof(struct ipv6hdr),
 283                                 IPPROTO_ICMPV6,
 284                                 csum_partial(icmp6h,
 285                                              nskb->len - sizeof(struct ipv6hdr),
 286                                              0));
 287
 288         nft_reject_br_push_etherhdr(oldskb, nskb);
 289
 290         br_forward(br_port_get_rcu(dev), nskb, false, true);
 291 }
 292
 293 static void nft_reject_bridge_eval(const struct nft_expr *expr,
 294                                    struct nft_regs *regs,
 295                                    const struct nft_pktinfo *pkt)
 296 {
 297         struct nft_reject *priv = nft_expr_priv(expr);
 298         const unsigned char *dest = eth_hdr(pkt->skb)->h_dest;
 299
 300         if (is_broadcast_ether_addr(dest) ||
 301             is_multicast_ether_addr(dest))
 302                 goto out;
 303
 304         switch (eth_hdr(pkt->skb)->h_proto) {
 305         case htons(ETH_P_IP):
 306                 switch (priv->type) {
 307                 case NFT_REJECT_ICMP_UNREACH:
 308                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 309                                                       nft_in(pkt),
 310                                                       nft_hook(pkt),
 311                                                       priv->icmp_code);
 312                         break;
 313                 case NFT_REJECT_TCP_RST:
 314                         nft_reject_br_send_v4_tcp_reset(nft_net(pkt), pkt->skb,
 315                                                         nft_in(pkt),
 316                                                         nft_hook(pkt));
 317                         break;
 318                 case NFT_REJECT_ICMPX_UNREACH:
 319                         nft_reject_br_send_v4_unreach(nft_net(pkt), pkt->skb,
 320                                                       nft_in(pkt),
 321                                                       nft_hook(pkt),
 322                                                       nft_reject_icmp_code(priv->icmp_code));
 323                         break;
 324                 }
 325                 break;
 326         case htons(ETH_P_IPV6):
 327                 switch (priv->type) {
 328                 case NFT_REJECT_ICMP_UNREACH:
 329                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 330                                                       nft_in(pkt),
 331                                                       nft_hook(pkt),
 332                                                       priv->icmp_code);
 333                         break;
 334                 case NFT_REJECT_TCP_RST:
 335                         nft_reject_br_send_v6_tcp_reset(nft_net(pkt), pkt->skb,
 336                                                         nft_in(pkt),
 337                                                         nft_hook(pkt));
 338                         break;
 339                 case NFT_REJECT_ICMPX_UNREACH:
 340                         nft_reject_br_send_v6_unreach(nft_net(pkt), pkt->skb,
 341                                                       nft_in(pkt),
 342                                                       nft_hook(pkt),
 343                                                       nft_reject_icmpv6_code(priv->icmp_code));
 344                         break;
 345                 }
 346                 break;
 347         default:
 348                 /* No explicit way to reject this protocol, drop it. */
 349                 break;
 350         }
 351 out:
 352         regs->verdict.code = NF_DROP;
 353 }
 354
 355 static int nft_reject_bridge_validate(const struct nft_ctx *ctx,
 356                                       const struct nft_expr *expr,
 357                                       const struct nft_data **data)
 358 {
 359         return nft_chain_validate_hooks(ctx->chain, (1 << NF_BR_PRE_ROUTING) |
 360                                                     (1 << NF_BR_LOCAL_IN));
 361 }
 362
 363 static int nft_reject_bridge_init(const struct nft_ctx *ctx,
 364                                   const struct nft_expr *expr,
 365                                   const struct nlattr * const tb[])
 366 {
 367         struct nft_reject *priv = nft_expr_priv(expr);
 368         int icmp_code;
 369
 370         if (tb[NFTA_REJECT_TYPE] == NULL)
 371                 return -EINVAL;
 372
 373         priv->type = ntohl(nla_get_be32(tb[NFTA_REJECT_TYPE]));
 374         switch (priv->type) {
 375         case NFT_REJECT_ICMP_UNREACH:
 376         case NFT_REJECT_ICMPX_UNREACH:
 377                 if (tb[NFTA_REJECT_ICMP_CODE] == NULL)
 378                         return -EINVAL;
 379
 380                 icmp_code = nla_get_u8(tb[NFTA_REJECT_ICMP_CODE]);
 381                 if (priv->type == NFT_REJECT_ICMPX_UNREACH &&
 382                     icmp_code > NFT_REJECT_ICMPX_MAX)
 383                         return -EINVAL;
 384
 385                 priv->icmp_code = icmp_code;
 386                 break;
 387         case NFT_REJECT_TCP_RST:
 388                 break;
 389         default:
 390                 return -EINVAL;
 391         }
 392         return 0;
 393 }
 394
 395 static int nft_reject_bridge_dump(struct sk_buff *skb,
 396                                   const struct nft_expr *expr)
 397 {
 398         const struct nft_reject *priv = nft_expr_priv(expr);
 399
 400         if (nla_put_be32(skb, NFTA_REJECT_TYPE, htonl(priv->type)))
 401                 goto nla_put_failure;
 402
 403         switch (priv->type) {
 404         case NFT_REJECT_ICMP_UNREACH:
 405         case NFT_REJECT_ICMPX_UNREACH:
 406                 if (nla_put_u8(skb, NFTA_REJECT_ICMP_CODE, priv->icmp_code))
 407                         goto nla_put_failure;
 408                 break;
 409         default:
 410                 break;
 411         }
 412
 413         return 0;
 414
 415 nla_put_failure:
 416         return -1;
 417 }
 418
 419 static struct nft_expr_type nft_reject_bridge_type;
 420 static const struct nft_expr_ops nft_reject_bridge_ops = {
 421         .type           = &nft_reject_bridge_type,
 422         .size           = NFT_EXPR_SIZE(sizeof(struct nft_reject)),
 423         .eval           = nft_reject_bridge_eval,
 424         .init           = nft_reject_bridge_init,
 425         .dump           = nft_reject_bridge_dump,
 426         .validate       = nft_reject_bridge_validate,
 427 };
 428
 429 static struct nft_expr_type nft_reject_bridge_type __read_mostly = {
 430         .family         = NFPROTO_BRIDGE,
 431         .name           = "reject",
 432         .ops            = &nft_reject_bridge_ops,
 433         .policy         = nft_reject_policy,
 434         .maxattr        = NFTA_REJECT_MAX,
 435         .owner          = THIS_MODULE,
 436 };
 437
 438 static int __init nft_reject_bridge_module_init(void)
 439 {
 440         return nft_register_expr(&nft_reject_bridge_type);
 441 }
 442
 443 static void __exit nft_reject_bridge_module_exit(void)
 444 {
 445         nft_unregister_expr(&nft_reject_bridge_type);
 446 }
 447
 448 module_init(nft_reject_bridge_module_init);
 449 module_exit(nft_reject_bridge_module_exit);
 450
 451 MODULE_LICENSE("GPL");
 452 MODULE_AUTHOR("Pablo Neira Ayuso <pablo@netfilter.org>");
 453 MODULE_ALIAS_NFT_AF_EXPR(AF_BRIDGE, "reject");