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                                      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;
  35         opts->mss = 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_expr *expr,
  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 nft_synproxy *priv = nft_expr_priv(expr);
  52         struct nf_synproxy_info info = priv->info;
  53         struct net *net = nft_net(pkt);
  54         struct synproxy_net *snet = synproxy_pernet(net);
  55         struct sk_buff *skb = pkt->skb;
  56
  57         if (tcp->syn) {
  58                 /* Initial SYN from client */
  59                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  60                 synproxy_send_client_synack(net, skb, tcp, opts);
  61                 consume_skb(skb);
  62                 regs->verdict.code = NF_STOLEN;
  63         } else if (tcp->ack) {
  64                 /* ACK from client */
  65                 if (synproxy_recv_client_ack(net, skb, tcp, opts,
  66                                              ntohl(tcp->seq))) {
  67                         consume_skb(skb);
  68                         regs->verdict.code = NF_STOLEN;
  69                 } else {
  70                         regs->verdict.code = NF_DROP;
  71                 }
  72         }
  73 }
  74
  75 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
  76 static void nft_synproxy_eval_v6(const struct nft_expr *expr,
  77                                  struct nft_regs *regs,
  78                                  const struct nft_pktinfo *pkt,
  79                                  const struct tcphdr *tcp,
  80                                  struct tcphdr *_tcph,
  81                                  struct synproxy_options *opts)
  82 {
  83         struct nft_synproxy *priv = nft_expr_priv(expr);
  84         struct nf_synproxy_info info = priv->info;
  85         struct net *net = nft_net(pkt);
  86         struct synproxy_net *snet = synproxy_pernet(net);
  87         struct sk_buff *skb = pkt->skb;
  88
  89         if (tcp->syn) {
  90                 /* Initial SYN from client */
  91                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  92                 synproxy_send_client_synack_ipv6(net, skb, tcp, opts);
  93                 consume_skb(skb);
  94                 regs->verdict.code = NF_STOLEN;
  95         } else if (tcp->ack) {
  96                 /* ACK from client */
  97                 if (synproxy_recv_client_ack_ipv6(net, skb, tcp, opts,
  98                                                   ntohl(tcp->seq))) {
  99                         consume_skb(skb);
 100                         regs->verdict.code = NF_STOLEN;
 101                 } else {
 102                         regs->verdict.code = NF_DROP;
 103                 }
 104         }
 105 }
 106 #endif /* CONFIG_NF_TABLES_IPV6*/
 107
 108 static void nft_synproxy_eval(const struct nft_expr *expr,
 109                               struct nft_regs *regs,
 110                               const struct nft_pktinfo *pkt)
 111 {
 112         struct synproxy_options opts = {};
 113         struct sk_buff *skb = pkt->skb;
 114         int thoff = pkt->xt.thoff;
 115         const struct tcphdr *tcp;
 116         struct tcphdr _tcph;
 117
 118         if (pkt->tprot != IPPROTO_TCP) {
 119                 regs->verdict.code = NFT_BREAK;
 120                 return;
 121         }
 122
 123         if (nf_ip_checksum(skb, nft_hook(pkt), thoff, IPPROTO_TCP)) {
 124                 regs->verdict.code = NF_DROP;
 125                 return;
 126         }
 127
 128         tcp = skb_header_pointer(skb, pkt->xt.thoff,
 129                                  sizeof(struct tcphdr),
 130                                  &_tcph);
 131         if (!tcp) {
 132                 regs->verdict.code = NF_DROP;
 133                 return;
 134         }
 135
 136         if (!synproxy_parse_options(skb, thoff, tcp, &opts)) {
 137                 regs->verdict.code = NF_DROP;
 138                 return;
 139         }
 140
 141         switch (skb->protocol) {
 142         case htons(ETH_P_IP):
 143                 nft_synproxy_eval_v4(expr, regs, pkt, tcp, &_tcph, &opts);
 144                 return;
 145 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 146         case htons(ETH_P_IPV6):
 147                 nft_synproxy_eval_v6(expr, regs, pkt, tcp, &_tcph, &opts);
 148                 return;
 149 #endif
 150         }
 151         regs->verdict.code = NFT_BREAK;
 152 }
 153
 154 static int nft_synproxy_init(const struct nft_ctx *ctx,
 155                              const struct nft_expr *expr,
 156                              const struct nlattr * const tb[])
 157 {
 158         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 159         struct nft_synproxy *priv = nft_expr_priv(expr);
 160         u32 flags;
 161         int err;
 162
 163         if (tb[NFTA_SYNPROXY_MSS])
 164                 priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
 165         if (tb[NFTA_SYNPROXY_WSCALE])
 166                 priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
 167         if (tb[NFTA_SYNPROXY_FLAGS]) {
 168                 flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
 169                 if (flags & ~NF_SYNPROXY_OPT_MASK)
 170                         return -EOPNOTSUPP;
 171                 priv->info.options = flags;
 172         }
 173
 174         err = nf_ct_netns_get(ctx->net, ctx->family);
 175         if (err)
 176                 return err;
 177
 178         switch (ctx->family) {
 179         case NFPROTO_IPV4:
 180                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 181                 if (err)
 182                         goto nf_ct_failure;
 183                 break;
 184 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 185         case NFPROTO_IPV6:
 186                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 187                 if (err)
 188                         goto nf_ct_failure;
 189                 break;
 190 #endif
 191         case NFPROTO_INET:
 192         case NFPROTO_BRIDGE:
 193                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 194                 if (err)
 195                         goto nf_ct_failure;
 196                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 197                 if (err)
 198                         goto nf_ct_failure;
 199                 break;
 200         }
 201
 202         return 0;
 203
 204 nf_ct_failure:
 205         nf_ct_netns_put(ctx->net, ctx->family);
 206         return err;
 207 }
 208
 209 static void nft_synproxy_destroy(const struct nft_ctx *ctx,
 210                                  const struct nft_expr *expr)
 211 {
 212         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 213
 214         switch (ctx->family) {
 215         case NFPROTO_IPV4:
 216                 nf_synproxy_ipv4_fini(snet, ctx->net);
 217                 break;
 218 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 219         case NFPROTO_IPV6:
 220                 nf_synproxy_ipv6_fini(snet, ctx->net);
 221                 break;
 222 #endif
 223         case NFPROTO_INET:
 224         case NFPROTO_BRIDGE:
 225                 nf_synproxy_ipv4_fini(snet, ctx->net);
 226                 nf_synproxy_ipv6_fini(snet, ctx->net);
 227                 break;
 228         }
 229         nf_ct_netns_put(ctx->net, ctx->family);
 230 }
 231
 232 static int nft_synproxy_dump(struct sk_buff *skb, const struct nft_expr *expr)
 233 {
 234         const struct nft_synproxy *priv = nft_expr_priv(expr);
 235
 236         if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
 237             nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
 238             nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
 239                 goto nla_put_failure;
 240
 241         return 0;
 242
 243 nla_put_failure:
 244         return -1;
 245 }
 246
 247 static int nft_synproxy_validate(const struct nft_ctx *ctx,
 248                                  const struct nft_expr *expr,
 249                                  const struct nft_data **data)
 250 {
 251         return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
 252                                                     (1 << NF_INET_FORWARD));
 253 }
 254
 255 static struct nft_expr_type nft_synproxy_type;
 256 static const struct nft_expr_ops nft_synproxy_ops = {
 257         .eval           = nft_synproxy_eval,
 258         .size           = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
 259         .init           = nft_synproxy_init,
 260         .destroy        = nft_synproxy_destroy,
 261         .dump           = nft_synproxy_dump,
 262         .type           = &nft_synproxy_type,
 263         .validate       = nft_synproxy_validate,
 264 };
 265
 266 static struct nft_expr_type nft_synproxy_type __read_mostly = {
 267         .ops            = &nft_synproxy_ops,
 268         .name           = "synproxy",
 269         .owner          = THIS_MODULE,
 270         .policy         = nft_synproxy_policy,
 271         .maxattr        = NFTA_SYNPROXY_MAX,
 272 };
 273
 274 static int __init nft_synproxy_module_init(void)
 275 {
 276         return nft_register_expr(&nft_synproxy_type);
 277 }
 278
 279 static void __exit nft_synproxy_module_exit(void)
 280 {
 281         return nft_unregister_expr(&nft_synproxy_type);
 282 }
 283
 284 module_init(nft_synproxy_module_init);
 285 module_exit(nft_synproxy_module_exit);
 286
 287 MODULE_LICENSE("GPL");
 288 MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
 289 MODULE_ALIAS_NFT_EXPR("synproxy");