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