nf_conntrack_proto_gre.c

  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
 45static 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 */
 51static DEFINE_SPINLOCK(keymap_lock);
 52
 53static inline struct nf_gre_net *gre_pernet(struct net *net)
 54{
 55	return &net->ct.nf_ct_proto.gre;
 56}
 57
 58static 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 */
 69static __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 */
 89int 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}
124EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_add);
125
126/* destroy the keymap entries associated with specified master ct */
127void 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}
146EXPORT_SYMBOL_GPL(nf_ct_gre_keymap_destroy);
147
148/* PUBLIC CONNTRACK PROTO HELPER FUNCTIONS */
149
150/* gre hdr info to tuple */
151bool 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 */
188static 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
196static 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 */
202int 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
248static 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
271static int
272gre_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
283nla_put_failure:
284	return -ENOSPC;
285}
286
287static const struct nla_policy
288gre_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
294void 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 */
305const 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};