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         if (opts->options & NF_SYNPROXY_OPT_TIMESTAMP)
  35                 synproxy_init_timestamp_cookie(info, opts);
  36         else
  37                 opts->options &= ~(NF_SYNPROXY_OPT_WSCALE |
  38                                    NF_SYNPROXY_OPT_SACK_PERM |
  39                                    NF_SYNPROXY_OPT_ECN);
  40 }
  41
  42 static void nft_synproxy_eval_v4(const struct nft_expr *expr,
  43                                  struct nft_regs *regs,
  44                                  const struct nft_pktinfo *pkt,
  45                                  const struct tcphdr *tcp,
  46                                  struct tcphdr *_tcph,
  47                                  struct synproxy_options *opts)
  48 {
  49         struct nft_synproxy *priv = nft_expr_priv(expr);
  50         struct nf_synproxy_info info = priv->info;
  51         struct net *net = nft_net(pkt);
  52         struct synproxy_net *snet = synproxy_pernet(net);
  53         struct sk_buff *skb = pkt->skb;
  54
  55         if (tcp->syn) {
  56                 /* Initial SYN from client */
  57                 nft_synproxy_tcp_options(opts, tcp, snet, &info, priv);
  58                 synproxy_send_client_synack(net, skb, tcp, opts);
  59                 consume_skb(skb);
  60                 regs->verdict.code = NF_STOLEN;
  61         } else if (tcp->ack) {
  62                 /* ACK from client */
  63                 if (synproxy_recv_client_ack(net, skb, tcp, opts,
  64                                              ntohl(tcp->seq))) {
  65                         consume_skb(skb);
  66                         regs->verdict.code = NF_STOLEN;
  67                 } else {
  68                         regs->verdict.code = NF_DROP;
  69                 }
  70         }
  71 }
  72
  73 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
  74 static void nft_synproxy_eval_v6(const struct nft_expr *expr,
  75                                  struct nft_regs *regs,
  76                                  const struct nft_pktinfo *pkt,
  77                                  const struct tcphdr *tcp,
  78                                  struct tcphdr *_tcph,
  79                                  struct synproxy_options *opts)
  80 {
  81         struct nft_synproxy *priv = nft_expr_priv(expr);
  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_eval(const struct nft_expr *expr,
 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 = pkt->xt.thoff;
 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, pkt->xt.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(expr, 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(expr, regs, pkt, tcp, &_tcph, &opts);
 146                 return;
 147 #endif
 148         }
 149         regs->verdict.code = NFT_BREAK;
 150 }
 151
 152 static int nft_synproxy_init(const struct nft_ctx *ctx,
 153                              const struct nft_expr *expr,
 154                              const struct nlattr * const tb[])
 155 {
 156         struct synproxy_net *snet = synproxy_pernet(ctx->net);
 157         struct nft_synproxy *priv = nft_expr_priv(expr);
 158         u32 flags;
 159         int err;
 160
 161         if (tb[NFTA_SYNPROXY_MSS])
 162                 priv->info.mss = ntohs(nla_get_be16(tb[NFTA_SYNPROXY_MSS]));
 163         if (tb[NFTA_SYNPROXY_WSCALE])
 164                 priv->info.wscale = nla_get_u8(tb[NFTA_SYNPROXY_WSCALE]);
 165         if (tb[NFTA_SYNPROXY_FLAGS]) {
 166                 flags = ntohl(nla_get_be32(tb[NFTA_SYNPROXY_FLAGS]));
 167                 if (flags & ~NF_SYNPROXY_OPT_MASK)
 168                         return -EOPNOTSUPP;
 169                 priv->info.options = flags;
 170         }
 171
 172         err = nf_ct_netns_get(ctx->net, ctx->family);
 173         if (err)
 174                 return err;
 175
 176         switch (ctx->family) {
 177         case NFPROTO_IPV4:
 178                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 179                 if (err)
 180                         goto nf_ct_failure;
 181                 break;
 182 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
 183         case NFPROTO_IPV6:
 184                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 185                 if (err)
 186                         goto nf_ct_failure;
 187                 break;
 188 #endif
 189         case NFPROTO_INET:
 190         case NFPROTO_BRIDGE:
 191                 err = nf_synproxy_ipv4_init(snet, ctx->net);
 192                 if (err)
 193                         goto nf_ct_failure;
 194                 err = nf_synproxy_ipv6_init(snet, ctx->net);
 195                 if (err)
 196                         goto nf_ct_failure;
 197                 break;
 198         }
 199
 200         return 0;
 201
 202 nf_ct_failure:
 203         nf_ct_netns_put(ctx->net, ctx->family);
 204         return err;
 205 }
 206
 207 static void nft_synproxy_destroy(const struct nft_ctx *ctx,
 208                                  const struct nft_expr *expr)
 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_dump(struct sk_buff *skb, const struct nft_expr *expr)
 231 {
 232         const struct nft_synproxy *priv = nft_expr_priv(expr);
 233
 234         if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
 235             nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
 236             nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
 237                 goto nla_put_failure;
 238
 239         return 0;
 240
 241 nla_put_failure:
 242         return -1;
 243 }
 244
 245 static int nft_synproxy_validate(const struct nft_ctx *ctx,
 246                                  const struct nft_expr *expr,
 247                                  const struct nft_data **data)
 248 {
 249         return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
 250                                                     (1 << NF_INET_FORWARD));
 251 }
 252
 253 static struct nft_expr_type nft_synproxy_type;
 254 static const struct nft_expr_ops nft_synproxy_ops = {
 255         .eval           = nft_synproxy_eval,
 256         .size           = NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
 257         .init           = nft_synproxy_init,
 258         .destroy        = nft_synproxy_destroy,
 259         .dump           = nft_synproxy_dump,
 260         .type           = &nft_synproxy_type,
 261         .validate       = nft_synproxy_validate,
 262 };
 263
 264 static struct nft_expr_type nft_synproxy_type __read_mostly = {
 265         .ops            = &nft_synproxy_ops,
 266         .name           = "synproxy",
 267         .owner          = THIS_MODULE,
 268         .policy         = nft_synproxy_policy,
 269         .maxattr        = NFTA_SYNPROXY_MAX,
 270 };
 271
 272 static int __init nft_synproxy_module_init(void)
 273 {
 274         return nft_register_expr(&nft_synproxy_type);
 275 }
 276
 277 static void __exit nft_synproxy_module_exit(void)
 278 {
 279         return nft_unregister_expr(&nft_synproxy_type);
 280 }
 281
 282 module_init(nft_synproxy_module_init);
 283 module_exit(nft_synproxy_module_exit);
 284
 285 MODULE_LICENSE("GPL");
 286 MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
 287 MODULE_ALIAS_NFT_EXPR("synproxy");