xref: /linux/net/netfilter/nf_conntrack_proto_gre.c (revision cdd5b5a9761fd66d17586e4f4ba6588c70e640ea)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Connection tracking protocol helper module for GRE.
4  *
5  * GRE is a generic encapsulation protocol, which is generally not very
6  * suited for NAT, as it has no protocol-specific part as port numbers.
7  *
8  * It has an optional key field, which may help us distinguishing two
9  * connections between the same two hosts.
10  *
11  * GRE is defined in RFC 1701 and RFC 1702, as well as RFC 2784
12  *
13  * PPTP is built on top of a modified version of GRE, and has a mandatory
14  * field called "CallID", which serves us for the same purpose as the key
15  * field in plain GRE.
16  *
17  * Documentation about PPTP can be found in RFC 2637
18  *
19  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
20  *
21  * Development of this code funded by Astaro AG (http://www.astaro.com/)
22  *
23  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
24  */
25 
26 #include <linux/module.h>
27 #include <linux/types.h>
28 #include <linux/timer.h>
29 #include <linux/list.h>
30 #include <linux/seq_file.h>
31 #include <linux/in.h>
32 #include <linux/netdevice.h>
33 #include <linux/skbuff.h>
34 #include <linux/slab.h>
35 #include <net/dst.h>
36 #include <net/net_namespace.h>
37 #include <net/netns/generic.h>
38 #include <net/netfilter/nf_conntrack_l4proto.h>
39 #include <net/netfilter/nf_conntrack_helper.h>
40 #include <net/netfilter/nf_conntrack_core.h>
41 #include <net/netfilter/nf_conntrack_timeout.h>
42 #include <linux/netfilter/nf_conntrack_proto_gre.h>
43 #include <linux/netfilter/nf_conntrack_pptp.h>
44 
45 static const unsigned int gre_timeouts[GRE_CT_MAX] = {
46 	[GRE_CT_UNREPLIED]	= 30*HZ,
47 	[GRE_CT_REPLIED]	= 180*HZ,
48 };
49 
50 /* used when expectation is added */
51 static DEFINE_SPINLOCK(keymap_lock);
52 
gre_pernet(struct net * net)53 static inline struct nf_gre_net *gre_pernet(struct net *net)
54 {
55 	return &net->ct.nf_ct_proto.gre;
56 }
57 
gre_key_cmpfn(const struct nf_ct_gre_keymap * km,const struct nf_conntrack_tuple * t)58 static inline int gre_key_cmpfn(const struct nf_ct_gre_keymap *km,
59 				const struct nf_conntrack_tuple *t)
60 {
61 	return km->tuple.src.l3num == t->src.l3num &&
62 	       !memcmp(&km->tuple.src.u3, &t->src.u3, sizeof(t->src.u3)) &&
63 	       !memcmp(&km->tuple.dst.u3, &t->dst.u3, sizeof(t->dst.u3)) &&
64 	       km->tuple.dst.protonum == t->dst.protonum &&
65 	       km->tuple.dst.u.all == t->dst.u.all;
66 }
67 
68 /* look up the source key for a given tuple */
gre_keymap_lookup(struct net * net,struct nf_conntrack_tuple * t)69 static __be16 gre_keymap_lookup(struct net *net, struct nf_conntrack_tuple *t)
70 {
71 	struct nf_gre_net *net_gre = gre_pernet(net);
72 	struct nf_ct_gre_keymap *km;
73 	__be16 key = 0;
74 
75 	list_for_each_entry_rcu(km, &net_gre->keymap_list, list) {
76 		if (gre_key_cmpfn(km, t)) {
77 			key = km->tuple.src.u.gre.key;
78 			break;
79 		}
80 	}
81 
82 	pr_debug("lookup src key 0x%x for ", key);
83 	nf_ct_dump_tuple(t);
84 
85 	return key;
86 }
87 
88 /* add a single keymap entry, associate with specified master ct */
nf_ct_gre_keymap_add(struct nf_conn * ct,enum ip_conntrack_dir dir,struct nf_conntrack_tuple * t)89 int nf_ct_gre_keymap_add(struct nf_conn *ct, enum ip_conntrack_dir dir,
90 			 struct nf_conntrack_tuple *t)
91 {
92 	struct net *net = nf_ct_net(ct);
93 	struct nf_gre_net *net_gre = gre_pernet(net);
94 	struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
95 	struct nf_ct_gre_keymap **kmp, *km;
96 
97 	kmp = &ct_pptp_info->keymap[dir];
98 	if (*kmp) {
99 		/* check whether it's a retransmission */
100 		list_for_each_entry_rcu(km, &net_gre->keymap_list, list) {
101 			if (gre_key_cmpfn(km, t) && km == *kmp)
102 				return 0;
103 		}
104 		pr_debug("trying to override keymap_%s for ct %p\n",
105 			 dir == IP_CT_DIR_REPLY ? "reply" : "orig", ct);
106 		return -EEXIST;
107 	}
108 
109 	km = kmalloc(sizeof(*km), GFP_ATOMIC);
110 	if (!km)
111 		return -ENOMEM;
112 	memcpy(&km->tuple, t, sizeof(*t));
113 	*kmp = km;
114 
115 	pr_debug("adding new entry %p: ", km);
116 	nf_ct_dump_tuple(&km->tuple);
117 
118 	spin_lock_bh(&keymap_lock);
119 	list_add_tail(&km->list, &net_gre->keymap_list);
120 	spin_unlock_bh(&keymap_lock);
121 
122 	return 0;
123 }
124 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
125 
126 /* destroy the keymap entries associated with specified master ct */
nf_ct_gre_keymap_destroy(struct nf_conn * ct)127 void nf_ct_gre_keymap_destroy(struct nf_conn *ct)
128 {
129 	struct nf_ct_pptp_master *ct_pptp_info = nfct_help_data(ct);
130 	enum ip_conntrack_dir dir;
131 
132 	pr_debug("entering for ct %p\n", ct);
133 
134 	spin_lock_bh(&keymap_lock);
135 	for (dir = IP_CT_DIR_ORIGINAL; dir < IP_CT_DIR_MAX; dir++) {
136 		if (ct_pptp_info->keymap[dir]) {
137 			pr_debug("removing %p from list\n",
138 				 ct_pptp_info->keymap[dir]);
139 			list_del_rcu(&ct_pptp_info->keymap[dir]->list);
140 			kfree_rcu(ct_pptp_info->keymap[dir], rcu);
141 			ct_pptp_info->keymap[dir] = NULL;
142 		}
143 	}
144 	spin_unlock_bh(&keymap_lock);
145 }
146 EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
147 
148 /* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
149 
150 /* gre hdr info to tuple */
gre_pkt_to_tuple(const struct sk_buff * skb,unsigned int dataoff,struct net * net,struct nf_conntrack_tuple * tuple)151 bool gre_pkt_to_tuple(const struct sk_buff *skb, unsigned int dataoff,
152 		      struct net *net, struct nf_conntrack_tuple *tuple)
153 {
154 	const struct pptp_gre_header *pgrehdr;
155 	struct pptp_gre_header _pgrehdr;
156 	__be16 srckey;
157 	const struct gre_base_hdr *grehdr;
158 	struct gre_base_hdr _grehdr;
159 
160 	/* first only delinearize old RFC1701 GRE header */
161 	grehdr = skb_header_pointer(skb, dataoff, sizeof(_grehdr), &_grehdr);
162 	if (!grehdr || (grehdr->flags & GRE_VERSION) != GRE_VERSION_1) {
163 		/* try to behave like "nf_conntrack_proto_generic" */
164 		tuple->src.u.all = 0;
165 		tuple->dst.u.all = 0;
166 		return true;
167 	}
168 
169 	/* PPTP header is variable length, only need up to the call_id field */
170 	pgrehdr = skb_header_pointer(skb, dataoff, 8, &_pgrehdr);
171 	if (!pgrehdr)
172 		return true;
173 
174 	if (grehdr->protocol != GRE_PROTO_PPP) {
175 		pr_debug("Unsupported GRE proto(0x%x)\n", ntohs(grehdr->protocol));
176 		return false;
177 	}
178 
179 	tuple->dst.u.gre.key = pgrehdr->call_id;
180 	srckey = gre_keymap_lookup(net, tuple);
181 	tuple->src.u.gre.key = srckey;
182 
183 	return true;
184 }
185 
186 #ifdef CONFIG_NF_CONNTRACK_PROCFS
187 /* print private data for conntrack */
gre_print_conntrack(struct seq_file * s,struct nf_conn * ct)188 static void gre_print_conntrack(struct seq_file *s, struct nf_conn *ct)
189 {
190 	seq_printf(s, "timeout=%u, stream_timeout=%u ",
191 		   (ct->proto.gre.timeout / HZ),
192 		   (ct->proto.gre.stream_timeout / HZ));
193 }
194 #endif
195 
gre_get_timeouts(struct net * net)196 static unsigned int *gre_get_timeouts(struct net *net)
197 {
198 	return gre_pernet(net)->timeouts;
199 }
200 
201 /* Returns verdict for packet, and may modify conntrack */
nf_conntrack_gre_packet(struct nf_conn * ct,struct sk_buff * skb,unsigned int dataoff,enum ip_conntrack_info ctinfo,const struct nf_hook_state * state)202 int nf_conntrack_gre_packet(struct nf_conn *ct,
203 			    struct sk_buff *skb,
204 			    unsigned int dataoff,
205 			    enum ip_conntrack_info ctinfo,
206 			    const struct nf_hook_state *state)
207 {
208 	unsigned long status;
209 
210 	if (!nf_ct_is_confirmed(ct)) {
211 		unsigned int *timeouts = nf_ct_timeout_lookup(ct);
212 
213 		if (!timeouts)
214 			timeouts = gre_get_timeouts(nf_ct_net(ct));
215 
216 		/* initialize to sane value.  Ideally a conntrack helper
217 		 * (e.g. in case of pptp) is increasing them */
218 		ct->proto.gre.stream_timeout = timeouts[GRE_CT_REPLIED];
219 		ct->proto.gre.timeout = timeouts[GRE_CT_UNREPLIED];
220 	}
221 
222 	status = READ_ONCE(ct->status);
223 	/* If we've seen traffic both ways, this is a GRE connection.
224 	 * Extend timeout. */
225 	if (status & IPS_SEEN_REPLY) {
226 		nf_ct_refresh_acct(ct, ctinfo, skb,
227 				   ct->proto.gre.stream_timeout);
228 
229 		/* never set ASSURED for IPS_NAT_CLASH, they time out soon */
230 		if (unlikely((status & IPS_NAT_CLASH)))
231 			return NF_ACCEPT;
232 
233 		/* Also, more likely to be important, and not a probe. */
234 		if (!test_and_set_bit(IPS_ASSURED_BIT, &ct->status))
235 			nf_conntrack_event_cache(IPCT_ASSURED, ct);
236 	} else
237 		nf_ct_refresh_acct(ct, ctinfo, skb,
238 				   ct->proto.gre.timeout);
239 
240 	return NF_ACCEPT;
241 }
242 
243 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
244 
245 #include <linux/netfilter/nfnetlink.h>
246 #include <linux/netfilter/nfnetlink_cttimeout.h>
247 
gre_timeout_nlattr_to_obj(struct nlattr * tb[],struct net * net,void * data)248 static int gre_timeout_nlattr_to_obj(struct nlattr *tb[],
249 				     struct net *net, void *data)
250 {
251 	unsigned int *timeouts = data;
252 	struct nf_gre_net *net_gre = gre_pernet(net);
253 
254 	if (!timeouts)
255 		timeouts = gre_get_timeouts(net);
256 	/* set default timeouts for GRE. */
257 	timeouts[GRE_CT_UNREPLIED] = net_gre->timeouts[GRE_CT_UNREPLIED];
258 	timeouts[GRE_CT_REPLIED] = net_gre->timeouts[GRE_CT_REPLIED];
259 
260 	if (tb[CTA_TIMEOUT_GRE_UNREPLIED]) {
261 		timeouts[GRE_CT_UNREPLIED] =
262 			ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_UNREPLIED])) * HZ;
263 	}
264 	if (tb[CTA_TIMEOUT_GRE_REPLIED]) {
265 		timeouts[GRE_CT_REPLIED] =
266 			ntohl(nla_get_be32(tb[CTA_TIMEOUT_GRE_REPLIED])) * HZ;
267 	}
268 	return 0;
269 }
270 
271 static int
gre_timeout_obj_to_nlattr(struct sk_buff * skb,const void * data)272 gre_timeout_obj_to_nlattr(struct sk_buff *skb, const void *data)
273 {
274 	const unsigned int *timeouts = data;
275 
276 	if (nla_put_be32(skb, CTA_TIMEOUT_GRE_UNREPLIED,
277 			 htonl(timeouts[GRE_CT_UNREPLIED] / HZ)) ||
278 	    nla_put_be32(skb, CTA_TIMEOUT_GRE_REPLIED,
279 			 htonl(timeouts[GRE_CT_REPLIED] / HZ)))
280 		goto nla_put_failure;
281 	return 0;
282 
283 nla_put_failure:
284 	return -ENOSPC;
285 }
286 
287 static const struct nla_policy
288 gre_timeout_nla_policy[CTA_TIMEOUT_GRE_MAX+1] = {
289 	[CTA_TIMEOUT_GRE_UNREPLIED]	= { .type = NLA_U32 },
290 	[CTA_TIMEOUT_GRE_REPLIED]	= { .type = NLA_U32 },
291 };
292 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
293 
nf_conntrack_gre_init_net(struct net * net)294 void nf_conntrack_gre_init_net(struct net *net)
295 {
296 	struct nf_gre_net *net_gre = gre_pernet(net);
297 	int i;
298 
299 	INIT_LIST_HEAD(&net_gre->keymap_list);
300 	for (i = 0; i < GRE_CT_MAX; i++)
301 		net_gre->timeouts[i] = gre_timeouts[i];
302 }
303 
304 /* protocol helper struct */
305 const struct nf_conntrack_l4proto nf_conntrack_l4proto_gre = {
306 	.l4proto	 = IPPROTO_GRE,
307 	.allow_clash	 = true,
308 #ifdef CONFIG_NF_CONNTRACK_PROCFS
309 	.print_conntrack = gre_print_conntrack,
310 #endif
311 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
312 	.tuple_to_nlattr = nf_ct_port_tuple_to_nlattr,
313 	.nlattr_tuple_size = nf_ct_port_nlattr_tuple_size,
314 	.nlattr_to_tuple = nf_ct_port_nlattr_to_tuple,
315 	.nla_policy	 = nf_ct_port_nla_policy,
316 #endif
317 #ifdef CONFIG_NF_CONNTRACK_TIMEOUT
318 	.ctnl_timeout    = {
319 		.nlattr_to_obj	= gre_timeout_nlattr_to_obj,
320 		.obj_to_nlattr	= gre_timeout_obj_to_nlattr,
321 		.nlattr_max	= CTA_TIMEOUT_GRE_MAX,
322 		.obj_size	= sizeof(unsigned int) * GRE_CT_MAX,
323 		.nla_policy	= gre_timeout_nla_policy,
324 	},
325 #endif /* CONFIG_NF_CONNTRACK_TIMEOUT */
326 };
327