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