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Linux/net/netfilter/nft_synproxy.c

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  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");
290 

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