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 
nft_synproxy_tcp_options(struct synproxy_options * opts,const struct tcphdr * tcp,struct synproxy_net * snet,struct nf_synproxy_info * info,const struct nft_synproxy * priv)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 
nft_synproxy_eval_v4(const struct nft_synproxy * priv,struct nft_regs * regs,const struct nft_pktinfo * pkt,const struct tcphdr * tcp,struct tcphdr * _tcph,struct synproxy_options * opts)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)
nft_synproxy_eval_v6(const struct nft_synproxy * priv,struct nft_regs * regs,const struct nft_pktinfo * pkt,const struct tcphdr * tcp,struct tcphdr * _tcph,struct synproxy_options * opts)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 
nft_synproxy_do_eval(const struct nft_synproxy * priv,struct nft_regs * regs,const struct nft_pktinfo * pkt)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 
nft_synproxy_do_init(const struct nft_ctx * ctx,const struct nlattr * const tb[],struct nft_synproxy * priv)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 		err = nf_synproxy_ipv4_init(snet, ctx->net);
190 		if (err)
191 			goto nf_ct_failure;
192 		err = nf_synproxy_ipv6_init(snet, ctx->net);
193 		if (err) {
194 			nf_synproxy_ipv4_fini(snet, ctx->net);
195 			goto nf_ct_failure;
196 		}
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 
nft_synproxy_do_destroy(const struct nft_ctx * ctx)207 static void nft_synproxy_do_destroy(const struct nft_ctx *ctx)
208 {
209 	struct synproxy_net *snet = synproxy_pernet(ctx->net);
210 
211 	switch (ctx->family) {
212 	case NFPROTO_IPV4:
213 		nf_synproxy_ipv4_fini(snet, ctx->net);
214 		break;
215 #if IS_ENABLED(CONFIG_NF_TABLES_IPV6)
216 	case NFPROTO_IPV6:
217 		nf_synproxy_ipv6_fini(snet, ctx->net);
218 		break;
219 #endif
220 	case NFPROTO_INET:
221 		nf_synproxy_ipv4_fini(snet, ctx->net);
222 		nf_synproxy_ipv6_fini(snet, ctx->net);
223 		break;
224 	}
225 	nf_ct_netns_put(ctx->net, ctx->family);
226 }
227 
nft_synproxy_do_dump(struct sk_buff * skb,struct nft_synproxy * priv)228 static int nft_synproxy_do_dump(struct sk_buff *skb, struct nft_synproxy *priv)
229 {
230 	if (nla_put_be16(skb, NFTA_SYNPROXY_MSS, htons(priv->info.mss)) ||
231 	    nla_put_u8(skb, NFTA_SYNPROXY_WSCALE, priv->info.wscale) ||
232 	    nla_put_be32(skb, NFTA_SYNPROXY_FLAGS, htonl(priv->info.options)))
233 		goto nla_put_failure;
234 
235 	return 0;
236 
237 nla_put_failure:
238 	return -1;
239 }
240 
nft_synproxy_eval(const struct nft_expr * expr,struct nft_regs * regs,const struct nft_pktinfo * pkt)241 static void nft_synproxy_eval(const struct nft_expr *expr,
242 			      struct nft_regs *regs,
243 			      const struct nft_pktinfo *pkt)
244 {
245 	const struct nft_synproxy *priv = nft_expr_priv(expr);
246 
247 	nft_synproxy_do_eval(priv, regs, pkt);
248 }
249 
nft_synproxy_validate(const struct nft_ctx * ctx,const struct nft_expr * expr)250 static int nft_synproxy_validate(const struct nft_ctx *ctx,
251 				 const struct nft_expr *expr)
252 {
253 	if (ctx->family != NFPROTO_IPV4 &&
254 	    ctx->family != NFPROTO_IPV6 &&
255 	    ctx->family != NFPROTO_INET)
256 		return -EOPNOTSUPP;
257 
258 	return nft_chain_validate_hooks(ctx->chain, (1 << NF_INET_LOCAL_IN) |
259 						    (1 << NF_INET_FORWARD));
260 }
261 
nft_synproxy_init(const struct nft_ctx * ctx,const struct nft_expr * expr,const struct nlattr * const tb[])262 static int nft_synproxy_init(const struct nft_ctx *ctx,
263 			     const struct nft_expr *expr,
264 			     const struct nlattr * const tb[])
265 {
266 	struct nft_synproxy *priv = nft_expr_priv(expr);
267 
268 	return nft_synproxy_do_init(ctx, tb, priv);
269 }
270 
nft_synproxy_destroy(const struct nft_ctx * ctx,const struct nft_expr * expr)271 static void nft_synproxy_destroy(const struct nft_ctx *ctx,
272 				 const struct nft_expr *expr)
273 {
274 	nft_synproxy_do_destroy(ctx);
275 }
276 
nft_synproxy_dump(struct sk_buff * skb,const struct nft_expr * expr,bool reset)277 static int nft_synproxy_dump(struct sk_buff *skb,
278 			     const struct nft_expr *expr, bool reset)
279 {
280 	struct nft_synproxy *priv = nft_expr_priv(expr);
281 
282 	return nft_synproxy_do_dump(skb, priv);
283 }
284 
285 static struct nft_expr_type nft_synproxy_type;
286 static const struct nft_expr_ops nft_synproxy_ops = {
287 	.eval		= nft_synproxy_eval,
288 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_synproxy)),
289 	.init		= nft_synproxy_init,
290 	.destroy	= nft_synproxy_destroy,
291 	.dump		= nft_synproxy_dump,
292 	.type		= &nft_synproxy_type,
293 	.validate	= nft_synproxy_validate,
294 	.reduce		= NFT_REDUCE_READONLY,
295 };
296 
297 static struct nft_expr_type nft_synproxy_type __read_mostly = {
298 	.ops		= &nft_synproxy_ops,
299 	.name		= "synproxy",
300 	.owner		= THIS_MODULE,
301 	.policy		= nft_synproxy_policy,
302 	.maxattr	= NFTA_SYNPROXY_MAX,
303 };
304 
nft_synproxy_obj_init(const struct nft_ctx * ctx,const struct nlattr * const tb[],struct nft_object * obj)305 static int nft_synproxy_obj_init(const struct nft_ctx *ctx,
306 				 const struct nlattr * const tb[],
307 				 struct nft_object *obj)
308 {
309 	struct nft_synproxy *priv = nft_obj_data(obj);
310 
311 	return nft_synproxy_do_init(ctx, tb, priv);
312 }
313 
nft_synproxy_obj_destroy(const struct nft_ctx * ctx,struct nft_object * obj)314 static void nft_synproxy_obj_destroy(const struct nft_ctx *ctx,
315 				     struct nft_object *obj)
316 {
317 	nft_synproxy_do_destroy(ctx);
318 }
319 
nft_synproxy_obj_dump(struct sk_buff * skb,struct nft_object * obj,bool reset)320 static int nft_synproxy_obj_dump(struct sk_buff *skb,
321 				 struct nft_object *obj, bool reset)
322 {
323 	struct nft_synproxy *priv = nft_obj_data(obj);
324 
325 	return nft_synproxy_do_dump(skb, priv);
326 }
327 
nft_synproxy_obj_eval(struct nft_object * obj,struct nft_regs * regs,const struct nft_pktinfo * pkt)328 static void nft_synproxy_obj_eval(struct nft_object *obj,
329 				  struct nft_regs *regs,
330 				  const struct nft_pktinfo *pkt)
331 {
332 	const struct nft_synproxy *priv = nft_obj_data(obj);
333 
334 	nft_synproxy_do_eval(priv, regs, pkt);
335 }
336 
nft_synproxy_obj_update(struct nft_object * obj,struct nft_object * newobj)337 static void nft_synproxy_obj_update(struct nft_object *obj,
338 				    struct nft_object *newobj)
339 {
340 	struct nft_synproxy *newpriv = nft_obj_data(newobj);
341 	struct nft_synproxy *priv = nft_obj_data(obj);
342 
343 	priv->info = newpriv->info;
344 }
345 
346 static struct nft_object_type nft_synproxy_obj_type;
347 static const struct nft_object_ops nft_synproxy_obj_ops = {
348 	.type		= &nft_synproxy_obj_type,
349 	.size		= sizeof(struct nft_synproxy),
350 	.init		= nft_synproxy_obj_init,
351 	.destroy	= nft_synproxy_obj_destroy,
352 	.dump		= nft_synproxy_obj_dump,
353 	.eval		= nft_synproxy_obj_eval,
354 	.update		= nft_synproxy_obj_update,
355 };
356 
357 static struct nft_object_type nft_synproxy_obj_type __read_mostly = {
358 	.type		= NFT_OBJECT_SYNPROXY,
359 	.ops		= &nft_synproxy_obj_ops,
360 	.maxattr	= NFTA_SYNPROXY_MAX,
361 	.policy		= nft_synproxy_policy,
362 	.owner		= THIS_MODULE,
363 };
364 
nft_synproxy_module_init(void)365 static int __init nft_synproxy_module_init(void)
366 {
367 	int err;
368 
369 	err = nft_register_obj(&nft_synproxy_obj_type);
370 	if (err < 0)
371 		return err;
372 
373 	err = nft_register_expr(&nft_synproxy_type);
374 	if (err < 0)
375 		goto err;
376 
377 	return 0;
378 
379 err:
380 	nft_unregister_obj(&nft_synproxy_obj_type);
381 	return err;
382 }
383 
nft_synproxy_module_exit(void)384 static void __exit nft_synproxy_module_exit(void)
385 {
386 	nft_unregister_expr(&nft_synproxy_type);
387 	nft_unregister_obj(&nft_synproxy_obj_type);
388 }
389 
390 module_init(nft_synproxy_module_init);
391 module_exit(nft_synproxy_module_exit);
392 
393 MODULE_LICENSE("GPL");
394 MODULE_AUTHOR("Fernando Fernandez <ffmancera@riseup.net>");
395 MODULE_ALIAS_NFT_EXPR("synproxy");
396 MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_SYNPROXY);
397 MODULE_DESCRIPTION("nftables SYNPROXY expression support");
398