net/netfilter/nft_synproxy.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #include <linux/types.h>
   3 #include <net/ip.h>
   4 #include <net/tcp.h>
   5 #include <net/netlink.h>
   6 #include <net/netfilter/nf_tables.h>
   7 #include <net/netfilter/nf_conntrack.h>
   8 #include <net/netfilter/nf_conntrack_synproxy.h>
   9 #include <net/netfilter/nf_synproxy.h>
  10 #include <linux/netfilter/nf_tables.h>
  11 #include <linux/netfilter/nf_synproxy.h>
  12
  13 struct nft_synproxy {
  14         struct nf_synproxy_info info;
  15 };
  16
  17 static const struct nla_policy nft_synproxy_policy[NFTA_SYNPROXY_MAX + 1] = {
  18         [NFTA_SYNPROXY_MSS]             = { .type = NLA_U16 },
  19         [NFTA_SYNPROXY_WSCALE]          = { .type = NLA_U8 },
  20         [NFTA_SYNPROXY_FLAGS]           = { .type = NLA_U32 },
  21 };
  22
  23 static void nft_synproxy_tcp_options(struct synproxy_options *opts,
  24                                      const struct tcphdr *tcp,
  25                                      struct synproxy_net *snet,
  26                                      struct nf_synproxy_info *info,
  27                                      const struct nft_synproxy *priv)
  28 {
  29         this_cpu_inc(snet->stats->syn_received);
  30         if (tcp->ece && tcp->cwr)
  31                 opts->options |= NF_SYNPROXY_OPT_ECN;
  32
  33         opts->options &= priv->info.options;
  34         opts->mss_encode = opts->mss_option;
  35         opts->mss_option = info->mss;
  36         if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
  37                 synproxy_init_timestamp_cookie(info, opts);
  38         else
  39                 opts->options &= ~(NF_SYNPROXY_OPT_WSCALE |
  40                                    NF_SYNPROXY_OPT_SACK_PERM |
  41                                    NF_SYNPROXY_OPT_ECN);
  42 }
  43
  44 static void nft_synproxy_eval_v4(const struct nft_synproxy *priv,
  45                                  struct nft_regs *regs,
  46                                  const struct nft_pktinfo *pkt,
  47                                  const struct tcphdr *tcp,
  48                                  struct tcphdr *_tcph,
  49                                  struct synproxy_options *opts)
  50 {
  51         struct nf_synproxy_info info = priv->info;
  52         struct net *net = nft_net(pkt);
  53         struct synproxy_net *snet = synproxy_pernet(net);
  54         struct sk_buff *skb = pkt->skb;
  55
  56         if (tcp->syn) {
  57                 /* Initial SYN from client */
  58                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  59                 synproxy_send_client_synack(net, skb, tcp, opts);
  60                 consume_skb(skb);
  61                 regs->verdict.code = NF_STOLEN;
  62         } else if (tcp->ack) {
  63                 /* ACK from client */
  64                 if (synproxy_recv_client_ack(net, skb, tcp, opts,
  65                                              ntohl(tcp->seq))) {
  66                         consume_skb(skb);
  67                         regs->verdict.code = NF_STOLEN;
  68                 } else {
  69                         regs->verdict.code = NF_DROP;
  70                 }
  71         }
  72 }
  73
  74 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
  75 static void nft_synproxy_eval_v6(const struct nft_synproxy *priv,
  76                                  struct nft_regs *regs,
  77                                  const struct nft_pktinfo *pkt,
  78                                  const struct tcphdr *tcp,
  79                                  struct tcphdr *_tcph,
  80                                  struct synproxy_options *opts)
  81 {
  82         struct nf_synproxy_info info = priv->info;
  83         struct net *net = nft_net(pkt);
  84         struct synproxy_net *snet = synproxy_pernet(net);
  85         struct sk_buff *skb = pkt->skb;
  86
  87         if (tcp->syn) {
  88                 /* Initial SYN from client */
  89                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  90                 synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
  91                 consume_skb(skb);
  92                 regs->verdict.code = NF_STOLEN;
  93         } else if (tcp->ack) {
  94                 /* ACK from client */
  95                 if (synproxy_recv_client_ack_ipv6(net, skb, tcp, opts,
  96                                                   ntohl(tcp->seq))) {
  97                         consume_skb(skb);
  98                         regs->verdict.code = NF_STOLEN;
  99                 } else {
 100                         regs->verdict.code = NF_DROP;
 101                 }
 102         }
 103 }
 104 #endif /* CONFIG_NF_TABLES_IPV6*/
 105
 106 static void nft_synproxy_do_eval(const struct nft_synproxy *priv,
 107                                  struct nft_regs *regs,
 108                                  const struct nft_pktinfo *pkt)
 109 {
 110         struct synproxy_options opts = {};
 111         struct sk_buff *skb = pkt->skb;
 112         int thoff = nft_thoff(pkt);
 113         const struct tcphdr *tcp;
 114         struct tcphdr _tcph;
 115
 116         if (pkt->tprot != IPPROTO_TCP) {
 117                 regs->verdict.code = NFT_BREAK;
 118                 return;
 119         }
 120
 121         if (nf_ip_checksum(skb, nft_hook(pkt), thoff, IPPROTO_TCP)) {
 122                 regs->verdict.code = NF_DROP;
 123                 return;
 124         }
 125
 126         tcp = skb_header_pointer(skb, thoff,
 127                                  sizeof(struct tcphdr),
 128                                  &_tcph);
 129         if (!tcp) {
 130                 regs->verdict.code = NF_DROP;
 131                 return;
 132         }
 133
 134         if (!synproxy_parse_options(skb, thoff, tcp, &opts)) {
 135                 regs->verdict.code = NF_DROP;
 136                 return;
 137         }
 138
 139         switch (skb->protocol) {
 140         case htons(ETH_P_IP):
 141                 nft_synproxy_eval_v4(priv, regs, pkt, tcp, &_tcph, &opts);
 142                 return;
 143 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 144         case htons(ETH_P_IPV6):
 145                 nft_synproxy_eval_v6(priv, regs, pkt, tcp, &_tcph, &opts);
 146                 return;
 147 #endif
 148         }
 149         regs->verdict.code = NFT_BREAK;
 150 }
 151
 152 static int nft_synproxy_do_init(const struct nft_ctx *ctx,
 153                                 const struct nlattr * const tb[],
 154                                 struct nft_synproxy *priv)
 155 {
 156         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 157         u32 flags;
 158         int err;
 159
 160         if (tb[NFTA_SYNPROXY_MSS])
 161                 priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
 162         if (tb[NFTA_SYNPROXY_WSCALE])
 163                 priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
 164         if (tb[NFTA_SYNPROXY_FLAGS]) {
 165                 flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
 166                 if (flags & ~NF_SYNPROXY_OPT_MASK)
 167                         return -EOPNOTSUPP;
 168                 priv->info.options = flags;
 169         }
 170
 171         err = nf_ct_netns_get(ctx->net, ctx->family);
 172         if (err)
 173                 return err;
 174
 175         switch (ctx->family) {
 176         case NFPROTO_IPV4:
 177                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 178                 if (err)
 179                         goto nf_ct_failure;
 180                 break;
 181 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 182         case NFPROTO_IPV6:
 183                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 184                 if (err)
 185                         goto nf_ct_failure;
 186                 break;
 187 #endif
 188         case NFPROTO_INET:
 189         case NFPROTO_BRIDGE:
 190                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 191                 if (err)
 192                         goto nf_ct_failure;
 193                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 194                 if (err) {
 195                         nf_synproxy_ipv4_fini(snet, ctx->net);
 196                         goto nf_ct_failure;
 197                 }
 198                 break;
 199         }
 200
 201         return 0;
 202
 203 nf_ct_failure:
 204         nf_ct_netns_put(ctx->net, ctx->family);
 205         return err;
 206 }
 207
 208 static void nft_synproxy_do_destroy(const struct nft_ctx *ctx)
 209 {
 210         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 211
 212         switch (ctx->family) {
 213         case NFPROTO_IPV4:
 214                 nf_synproxy_ipv4_fini(snet, ctx->net);
 215                 break;
 216 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 217         case NFPROTO_IPV6:
 218                 nf_synproxy_ipv6_fini(snet, ctx->net);
 219                 break;
 220 #endif
 221         case NFPROTO_INET:
 222         case NFPROTO_BRIDGE:
 223                 nf_synproxy_ipv4_fini(snet, ctx->net);
 224                 nf_synproxy_ipv6_fini(snet, ctx->net);
 225                 break;
 226         }
 227         nf_ct_netns_put(ctx->net, ctx->family);
 228 }
 229
 230 static int nft_synproxy_do_dump(struct sk_buff *skb, struct nft_synproxy *priv)
 231 {
 232         if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
 233             nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
 234             nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
 235                 goto nla_put_failure;
 236
 237         return 0;
 238
 239 nla_put_failure:
 240         return -1;
 241 }
 242
 243 static void nft_synproxy_eval(const struct nft_expr *expr,
 244                               struct nft_regs *regs,
 245                               const struct nft_pktinfo *pkt)
 246 {
 247         const struct nft_synproxy *priv = nft_expr_priv(expr);
 248
 249         nft_synproxy_do_eval(priv, regs, pkt);
 250 }
 251
 252 static int nft_synproxy_validate(const struct nft_ctx *ctx,
 253                                  const struct nft_expr *expr,
 254                                  const struct nft_data **data)
 255 {
 256         return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
 257                                                     (1 << NF_INET_FORWARD));
 258 }
 259
 260 static int nft_synproxy_init(const struct nft_ctx *ctx,
 261                              const struct nft_expr *expr,
 262                              const struct nlattr * const tb[])
 263 {
 264         struct nft_synproxy *priv = nft_expr_priv(expr);
 265
 266         return nft_synproxy_do_init(ctx, tb, priv);
 267 }
 268
 269 static void nft_synproxy_destroy(const struct nft_ctx *ctx,
 270                                  const struct nft_expr *expr)
 271 {
 272         nft_synproxy_do_destroy(ctx);
 273 }
 274
 275 static int nft_synproxy_dump(struct sk_buff *skb, const struct nft_expr *expr)
 276 {
 277         struct nft_synproxy *priv = nft_expr_priv(expr);
 278
 279         return nft_synproxy_do_dump(skb, priv);
 280 }
 281
 282 static struct nft_expr_type nft_synproxy_type;
 283 static const struct nft_expr_ops nft_synproxy_ops = {
 284         .eval           = nft_synproxy_eval,
 285         .size           = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
 286         .init           = nft_synproxy_init,
 287         .destroy        = nft_synproxy_destroy,
 288         .dump           = nft_synproxy_dump,
 289         .type           = &nft_synproxy_type,
 290         .validate       = nft_synproxy_validate,
 291 };
 292
 293 static struct nft_expr_type nft_synproxy_type __read_mostly = {
 294         .ops            = &nft_synproxy_ops,
 295         .name           = "synproxy",
 296         .owner          = THIS_MODULE,
 297         .policy         = nft_synproxy_policy,
 298         .maxattr        = NFTA_SYNPROXY_MAX,
 299 };
 300
 301 static int nft_synproxy_obj_init(const struct nft_ctx *ctx,
 302                                  const struct nlattr * const tb[],
 303                                  struct nft_object *obj)
 304 {
 305         struct nft_synproxy *priv = nft_obj_data(obj);
 306
 307         return nft_synproxy_do_init(ctx, tb, priv);
 308 }
 309
 310 static void nft_synproxy_obj_destroy(const struct nft_ctx *ctx,
 311                                      struct nft_object *obj)
 312 {
 313         nft_synproxy_do_destroy(ctx);
 314 }
 315
 316 static int nft_synproxy_obj_dump(struct sk_buff *skb,
 317                                  struct nft_object *obj, bool reset)
 318 {
 319         struct nft_synproxy *priv = nft_obj_data(obj);
 320
 321         return nft_synproxy_do_dump(skb, priv);
 322 }
 323
 324 static void nft_synproxy_obj_eval(struct nft_object *obj,
 325                                   struct nft_regs *regs,
 326                                   const struct nft_pktinfo *pkt)
 327 {
 328         const struct nft_synproxy *priv = nft_obj_data(obj);
 329
 330         nft_synproxy_do_eval(priv, regs, pkt);
 331 }
 332
 333 static void nft_synproxy_obj_update(struct nft_object *obj,
 334                                     struct nft_object *newobj)
 335 {
 336         struct nft_synproxy *newpriv = nft_obj_data(newobj);
 337         struct nft_synproxy *priv = nft_obj_data(obj);
 338
 339         priv->info = newpriv->info;
 340 }
 341
 342 static struct nft_object_type nft_synproxy_obj_type;
 343 static const struct nft_object_ops nft_synproxy_obj_ops = {
 344         .type           = &nft_synproxy_obj_type,
 345         .size           = sizeof(struct nft_synproxy),
 346         .init           = nft_synproxy_obj_init,
 347         .destroy        = nft_synproxy_obj_destroy,
 348         .dump           = nft_synproxy_obj_dump,
 349         .eval           = nft_synproxy_obj_eval,
 350         .update         = nft_synproxy_obj_update,
 351 };
 352
 353 static struct nft_object_type nft_synproxy_obj_type __read_mostly = {
 354         .type           = NFT_OBJECT_SYNPROXY,
 355         .ops            = &nft_synproxy_obj_ops,
 356         .maxattr        = NFTA_SYNPROXY_MAX,
 357         .policy         = nft_synproxy_policy,
 358         .owner          = THIS_MODULE,
 359 };
 360
 361 static int __init nft_synproxy_module_init(void)
 362 {
 363         int err;
 364
 365         err = nft_register_obj(&nft_synproxy_obj_type);
 366         if (err < 0)
 367                 return err;
 368
 369         err = nft_register_expr(&nft_synproxy_type);
 370         if (err < 0)
 371                 goto err;
 372
 373         return 0;
 374
 375 err:
 376         nft_unregister_obj(&nft_synproxy_obj_type);
 377         return err;
 378 }
 379
 380 static void __exit nft_synproxy_module_exit(void)
 381 {
 382         nft_unregister_expr(&nft_synproxy_type);
 383         nft_unregister_obj(&nft_synproxy_obj_type);
 384 }
 385
 386 module_init(nft_synproxy_module_init);
 387 module_exit(nft_synproxy_module_exit);
 388
 389 MODULE_LICENSE("GPL");
 390 MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
 391 MODULE_ALIAS_NFT_EXPR("synproxy");
 392 MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_SYNPROXY);
 393 MODULE_DESCRIPTION("nftables SYNPROXY expression support");