xref: /linux/net/netfilter/nf_conntrack_proto_icmp.c (revision 762f99f4f3cb41a775b5157dd761217beba65873)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /* (C) 1999-2001 Paul `Rusty' Russell
3  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
4  * (C) 2006-2010 Patrick McHardy <kaber@trash.net>
5  */
6 
7 #include <linux/types.h>
8 #include <linux/timer.h>
9 #include <linux/netfilter.h>
10 #include <linux/in.h>
11 #include <linux/icmp.h>
12 #include <linux/seq_file.h>
13 #include <net/ip.h>
14 #include <net/checksum.h>
15 #include <linux/netfilter_ipv4.h>
16 #include <net/netfilter/nf_conntrack_tuple.h>
17 #include <net/netfilter/nf_conntrack_l4proto.h>
18 #include <net/netfilter/nf_conntrack_core.h>
19 #include <net/netfilter/nf_conntrack_timeout.h>
20 #include <net/netfilter/nf_conntrack_zones.h>
21 #include <net/netfilter/nf_log.h>
22 
23 #include "nf_internals.h"
24 
25 static const unsigned int nf_ct_icmp_timeout = 30*HZ;
26 
icmp_pkt_to_tuple(const struct sk_buff * skb,unsigned int dataoff,struct net * net,struct nf_conntrack_tuple * tuple)27 bool icmp_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
28 		       struct net *net, struct nf_conntrack_tuple *tuple)
29 {
30 	const struct icmphdr *hp;
31 	struct icmphdr _hdr;
32 
33 	hp = skb_header_pointer(skb, dataoff, sizeof(_hdr), &_hdr);
34 	if (hp == NULL)
35 		return false;
36 
37 	tuple->dst.u.icmp.type = hp->type;
38 	tuple->src.u.icmp.id = hp->un.echo.id;
39 	tuple->dst.u.icmp.code = hp->code;
40 
41 	return true;
42 }
43 
44 /* Add 1; spaces filled with 0. */
45 static const u_int8_t invmap[] = {
46 	[ICMP_ECHO] = ICMP_ECHOREPLY + 1,
47 	[ICMP_ECHOREPLY] = ICMP_ECHO + 1,
48 	[ICMP_TIMESTAMP] = ICMP_TIMESTAMPREPLY + 1,
49 	[ICMP_TIMESTAMPREPLY] = ICMP_TIMESTAMP + 1,
50 	[ICMP_INFO_REQUEST] = ICMP_INFO_REPLY + 1,
51 	[ICMP_INFO_REPLY] = ICMP_INFO_REQUEST + 1,
52 	[ICMP_ADDRESS] = ICMP_ADDRESSREPLY + 1,
53 	[ICMP_ADDRESSREPLY] = ICMP_ADDRESS + 1
54 };
55 
nf_conntrack_invert_icmp_tuple(struct nf_conntrack_tuple * tuple,const struct nf_conntrack_tuple * orig)56 bool nf_conntrack_invert_icmp_tuple(struct nf_conntrack_tuple *tuple,
57 				    const struct nf_conntrack_tuple *orig)
58 {
59 	if (orig->dst.u.icmp.type >= sizeof(invmap) ||
60 	    !invmap[orig->dst.u.icmp.type])
61 		return false;
62 
63 	tuple->src.u.icmp.id = orig->src.u.icmp.id;
64 	tuple->dst.u.icmp.type = invmap[orig->dst.u.icmp.type] - 1;
65 	tuple->dst.u.icmp.code = orig->dst.u.icmp.code;
66 	return true;
67 }
68 
69 /* Returns verdict for packet, or -1 for invalid. */
nf_conntrack_icmp_packet(struct nf_conn * ct,struct sk_buff * skb,enum ip_conntrack_info ctinfo,const struct nf_hook_state * state)70 int nf_conntrack_icmp_packet(struct nf_conn *ct,
71 			     struct sk_buff *skb,
72 			     enum ip_conntrack_info ctinfo,
73 			     const struct nf_hook_state *state)
74 {
75 	/* Do not immediately delete the connection after the first
76 	   successful reply to avoid excessive conntrackd traffic
77 	   and also to handle correctly ICMP echo reply duplicates. */
78 	unsigned int *timeout = nf_ct_timeout_lookup(ct);
79 	static const u_int8_t valid_new[] = {
80 		[ICMP_ECHO] = 1,
81 		[ICMP_TIMESTAMP] = 1,
82 		[ICMP_INFO_REQUEST] = 1,
83 		[ICMP_ADDRESS] = 1
84 	};
85 
86 	if (state->pf != NFPROTO_IPV4)
87 		return -NF_ACCEPT;
88 
89 	if (ct->tuplehash[0].tuple.dst.u.icmp.type >= sizeof(valid_new) ||
90 	    !valid_new[ct->tuplehash[0].tuple.dst.u.icmp.type]) {
91 		/* Can't create a new ICMP `conn' with this. */
92 		pr_debug("icmp: can't create new conn with type %u\n",
93 			 ct->tuplehash[0].tuple.dst.u.icmp.type);
94 		nf_ct_dump_tuple_ip(&ct->tuplehash[0].tuple);
95 		return -NF_ACCEPT;
96 	}
97 
98 	if (!timeout)
99 		timeout = &nf_icmp_pernet(nf_ct_net(ct))->timeout;
100 
101 	nf_ct_refresh_acct(ct, ctinfo, skb, *timeout);
102 	return NF_ACCEPT;
103 }
104 
105 /* Check inner header is related to any of the existing connections */
nf_conntrack_inet_error(struct nf_conn * tmpl,struct sk_buff * skb,unsigned int dataoff,const struct nf_hook_state * state,u8 l4proto,union nf_inet_addr * outer_daddr)106 int nf_conntrack_inet_error(struct nf_conn *tmpl, struct sk_buff *skb,
107 			    unsigned int dataoff,
108 			    const struct nf_hook_state *state,
109 			    u8 l4proto, union nf_inet_addr *outer_daddr)
110 {
111 	struct nf_conntrack_tuple innertuple, origtuple;
112 	const struct nf_conntrack_tuple_hash *h;
113 	const struct nf_conntrack_zone *zone;
114 	enum ip_conntrack_info ctinfo;
115 	struct nf_conntrack_zone tmp;
116 	union nf_inet_addr *ct_daddr;
117 	enum ip_conntrack_dir dir;
118 	struct nf_conn *ct;
119 
120 	WARN_ON(skb_nfct(skb));
121 	zone = nf_ct_zone_tmpl(tmpl, skb, &tmp);
122 
123 	/* Are they talking about one of our connections? */
124 	if (!nf_ct_get_tuplepr(skb, dataoff,
125 			       state->pf, state->net, &origtuple))
126 		return -NF_ACCEPT;
127 
128 	/* Ordinarily, we'd expect the inverted tupleproto, but it's
129 	   been preserved inside the ICMP. */
130 	if (!nf_ct_invert_tuple(&innertuple, &origtuple))
131 		return -NF_ACCEPT;
132 
133 	h = nf_conntrack_find_get(state->net, zone, &innertuple);
134 	if (!h)
135 		return -NF_ACCEPT;
136 
137 	/* Consider: A -> T (=This machine) -> B
138 	 *   Conntrack entry will look like this:
139 	 *      Original:  A->B
140 	 *      Reply:     B->T (SNAT case) OR A
141 	 *
142 	 * When this function runs, we got packet that looks like this:
143 	 * iphdr|icmphdr|inner_iphdr|l4header (tcp, udp, ..).
144 	 *
145 	 * Above nf_conntrack_find_get() makes lookup based on inner_hdr,
146 	 * so we should expect that destination of the found connection
147 	 * matches outer header destination address.
148 	 *
149 	 * In above example, we can consider these two cases:
150 	 *  1. Error coming in reply direction from B or M (middle box) to
151 	 *     T (SNAT case) or A.
152 	 *     Inner saddr will be B, dst will be T or A.
153 	 *     The found conntrack will be reply tuple (B->T/A).
154 	 *  2. Error coming in original direction from A or M to B.
155 	 *     Inner saddr will be A, inner daddr will be B.
156 	 *     The found conntrack will be original tuple (A->B).
157 	 *
158 	 * In both cases, conntrack[dir].dst == inner.dst.
159 	 *
160 	 * A bogus packet could look like this:
161 	 *   Inner: B->T
162 	 *   Outer: B->X (other machine reachable by T).
163 	 *
164 	 * In this case, lookup yields connection A->B and will
165 	 * set packet from B->X as *RELATED*, even though no connection
166 	 * from X was ever seen.
167 	 */
168 	ct = nf_ct_tuplehash_to_ctrack(h);
169 	dir = NF_CT_DIRECTION(h);
170 	ct_daddr = &ct->tuplehash[dir].tuple.dst.u3;
171 	if (!nf_inet_addr_cmp(outer_daddr, ct_daddr)) {
172 		if (state->pf == AF_INET) {
173 			nf_l4proto_log_invalid(skb, state,
174 					       l4proto,
175 					       "outer daddr %pI4 != inner %pI4",
176 					       &outer_daddr->ip, &ct_daddr->ip);
177 		} else if (state->pf == AF_INET6) {
178 			nf_l4proto_log_invalid(skb, state,
179 					       l4proto,
180 					       "outer daddr %pI6 != inner %pI6",
181 					       &outer_daddr->ip6, &ct_daddr->ip6);
182 		}
183 		nf_ct_put(ct);
184 		return -NF_ACCEPT;
185 	}
186 
187 	ctinfo = IP_CT_RELATED;
188 	if (dir == IP_CT_DIR_REPLY)
189 		ctinfo += IP_CT_IS_REPLY;
190 
191 	/* Update skb to refer to this connection */
192 	nf_ct_set(skb, ct, ctinfo);
193 	return NF_ACCEPT;
194 }
195 
icmp_error_log(const struct sk_buff * skb,const struct nf_hook_state * state,const char * msg)196 static void icmp_error_log(const struct sk_buff *skb,
197 			   const struct nf_hook_state *state,
198 			   const char *msg)
199 {
200 	nf_l4proto_log_invalid(skb, state, IPPROTO_ICMP, "%s", msg);
201 }
202 
203 /* Small and modified version of icmp_rcv */
nf_conntrack_icmpv4_error(struct nf_conn * tmpl,struct sk_buff * skb,unsigned int dataoff,const struct nf_hook_state * state)204 int nf_conntrack_icmpv4_error(struct nf_conn *tmpl,
205 			      struct sk_buff *skb, unsigned int dataoff,
206 			      const struct nf_hook_state *state)
207 {
208 	union nf_inet_addr outer_daddr;
209 	const struct icmphdr *icmph;
210 	struct icmphdr _ih;
211 
212 	/* Not enough header? */
213 	icmph = skb_header_pointer(skb, dataoff, sizeof(_ih), &_ih);
214 	if (icmph == NULL) {
215 		icmp_error_log(skb, state, "short packet");
216 		return -NF_ACCEPT;
217 	}
218 
219 	/* See nf_conntrack_proto_tcp.c */
220 	if (state->net->ct.sysctl_checksum &&
221 	    state->hook == NF_INET_PRE_ROUTING &&
222 	    nf_ip_checksum(skb, state->hook, dataoff, IPPROTO_ICMP)) {
223 		icmp_error_log(skb, state, "bad hw icmp checksum");
224 		return -NF_ACCEPT;
225 	}
226 
227 	/*
228 	 *	18 is the highest 'known' ICMP type. Anything else is a mystery
229 	 *
230 	 *	RFC 1122: 3.2.2  Unknown ICMP messages types MUST be silently
231 	 *		  discarded.
232 	 */
233 	if (icmph->type > NR_ICMP_TYPES) {
234 		icmp_error_log(skb, state, "invalid icmp type");
235 		return -NF_ACCEPT;
236 	}
237 
238 	/* Need to track icmp error message? */
239 	if (!icmp_is_err(icmph->type))
240 		return NF_ACCEPT;
241 
242 	memset(&outer_daddr, 0, sizeof(outer_daddr));
243 	outer_daddr.ip = ip_hdr(skb)->daddr;
244 
245 	dataoff += sizeof(*icmph);
246 	return nf_conntrack_inet_error(tmpl, skb, dataoff, state,
247 				       IPPROTO_ICMP, &outer_daddr);
248 }
249 
250 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
251 
252 #include <linux/netfilter/nfnetlink.h>
253 #include <linux/netfilter/nfnetlink_conntrack.h>
254 
icmp_tuple_to_nlattr(struct sk_buff * skb,const struct nf_conntrack_tuple * t)255 static int icmp_tuple_to_nlattr(struct sk_buff *skb,
256 				const struct nf_conntrack_tuple *t)
257 {
258 	if (nla_put_be16(skb, CTA_PROTO_ICMP_ID, t->src.u.icmp.id) ||
259 	    nla_put_u8(skb, CTA_PROTO_ICMP_TYPE, t->dst.u.icmp.type) ||
260 	    nla_put_u8(skb, CTA_PROTO_ICMP_CODE, t->dst.u.icmp.code))
261 		goto nla_put_failure;
262 	return 0;
263 
264 nla_put_failure:
265 	return -1;
266 }
267 
268 static const struct nla_policy icmp_nla_policy[CTA_PROTO_MAX+1] = {
269 	[CTA_PROTO_ICMP_TYPE]	= { .type = NLA_U8 },
270 	[CTA_PROTO_ICMP_CODE]	= { .type = NLA_U8 },
271 	[CTA_PROTO_ICMP_ID]	= { .type = NLA_U16 },
272 };
273 
icmp_nlattr_to_tuple(struct nlattr * tb[],struct nf_conntrack_tuple * tuple,u_int32_t flags)274 static int icmp_nlattr_to_tuple(struct nlattr *tb[],
275 				struct nf_conntrack_tuple *tuple,
276 				u_int32_t flags)
277 {
278 	if (flags & CTA_FILTER_FLAG(CTA_PROTO_ICMP_TYPE)) {
279 		if (!tb[CTA_PROTO_ICMP_TYPE])
280 			return -EINVAL;
281 
282 		tuple->dst.u.icmp.type = nla_get_u8(tb[CTA_PROTO_ICMP_TYPE]);
283 		if (tuple->dst.u.icmp.type >= sizeof(invmap) ||
284 		    !invmap[tuple->dst.u.icmp.type])
285 			return -EINVAL;
286 	}
287 
288 	if (flags & CTA_FILTER_FLAG(CTA_PROTO_ICMP_CODE)) {
289 		if (!tb[CTA_PROTO_ICMP_CODE])
290 			return -EINVAL;
291 
292 		tuple->dst.u.icmp.code = nla_get_u8(tb[CTA_PROTO_ICMP_CODE]);
293 	}
294 
295 	if (flags & CTA_FILTER_FLAG(CTA_PROTO_ICMP_ID)) {
296 		if (!tb[CTA_PROTO_ICMP_ID])
297 			return -EINVAL;
298 
299 		tuple->src.u.icmp.id = nla_get_be16(tb[CTA_PROTO_ICMP_ID]);
300 	}
301 
302 	return 0;
303 }
304 
icmp_nlattr_tuple_size(void)305 static unsigned int icmp_nlattr_tuple_size(void)
306 {
307 	static unsigned int size __read_mostly;
308 
309 	if (!size)
310 		size = nla_policy_len(icmp_nla_policy, CTA_PROTO_MAX + 1);
311 
312 	return size;
313 }
314 #endif
315 
316 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
317 
318 #include <linux/netfilter/nfnetlink.h>
319 #include <linux/netfilter/nfnetlink_cttimeout.h>
320 
icmp_timeout_nlattr_to_obj(struct nlattr * tb[],struct net * net,void * data)321 static int icmp_timeout_nlattr_to_obj(struct nlattr *tb[],
322 				      struct net *net, void *data)
323 {
324 	unsigned int *timeout = data;
325 	struct nf_icmp_net *in = nf_icmp_pernet(net);
326 
327 	if (tb[CTA_TIMEOUT_ICMP_TIMEOUT]) {
328 		if (!timeout)
329 			timeout = &in->timeout;
330 		*timeout =
331 			ntohl(nla_get_be32(tb[CTA_TIMEOUT_ICMP_TIMEOUT])) * HZ;
332 	} else if (timeout) {
333 		/* Set default ICMP timeout. */
334 		*timeout = in->timeout;
335 	}
336 	return 0;
337 }
338 
339 static int
icmp_timeout_obj_to_nlattr(struct sk_buff * skb,const void * data)340 icmp_timeout_obj_to_nlattr(struct sk_buff *skb, const void *data)
341 {
342 	const unsigned int *timeout = data;
343 
344 	if (nla_put_be32(skb, CTA_TIMEOUT_ICMP_TIMEOUT, htonl(*timeout / HZ)))
345 		goto nla_put_failure;
346 	return 0;
347 
348 nla_put_failure:
349 	return -ENOSPC;
350 }
351 
352 static const struct nla_policy
353 icmp_timeout_nla_policy[CTA_TIMEOUT_ICMP_MAX+1] = {
354 	[CTA_TIMEOUT_ICMP_TIMEOUT]	= { .type = NLA_U32 },
355 };
356 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
357 
nf_conntrack_icmp_init_net(struct net * net)358 void nf_conntrack_icmp_init_net(struct net *net)
359 {
360 	struct nf_icmp_net *in = nf_icmp_pernet(net);
361 
362 	in->timeout = nf_ct_icmp_timeout;
363 }
364 
365 const struct nf_conntrack_l4proto nf_conntrack_l4proto_icmp =
366 {
367 	.l4proto		= IPPROTO_ICMP,
368 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
369 	.tuple_to_nlattr	= icmp_tuple_to_nlattr,
370 	.nlattr_tuple_size	= icmp_nlattr_tuple_size,
371 	.nlattr_to_tuple	= icmp_nlattr_to_tuple,
372 	.nla_policy		= icmp_nla_policy,
373 #endif
374 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
375 	.ctnl_timeout		= {
376 		.nlattr_to_obj	= icmp_timeout_nlattr_to_obj,
377 		.obj_to_nlattr	= icmp_timeout_obj_to_nlattr,
378 		.nlattr_max	= CTA_TIMEOUT_ICMP_MAX,
379 		.obj_size	= sizeof(unsigned int),
380 		.nla_policy	= icmp_timeout_nla_policy,
381 	},
382 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
383 };
384