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(p: &km->tuple.src.u3, q: &t->src.u3, size: sizeof(t->src.u3)) &&
63 !memcmp(p: &km->tuple.dst.u3, q: &t->dst.u3, size: 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(size: 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(t: &km->tuple);
117
118 spin_lock_bh(lock: &keymap_lock);
119 list_add_tail(new: &km->list, head: &net_gre->keymap_list);
120 spin_unlock_bh(lock: &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(lock: &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(entry: &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(lock: &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, offset: dataoff, len: sizeof(_grehdr), buffer: &_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, offset: dataoff, len: 8, buffer: &_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, t: 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(m: s, fmt: "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(net: 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 extra_jiffies: 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(nr: IPS_ASSURED_BIT, addr: &ct->status))
235 nf_conntrack_event_cache(event: IPCT_ASSURED, ct);
236 } else
237 nf_ct_refresh_acct(ct, ctinfo, skb,
238 extra_jiffies: 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, attrtype: CTA_TIMEOUT_GRE_UNREPLIED,
277 htonl(timeouts[GRE_CT_UNREPLIED] / HZ)) ||
278 nla_put_be32(skb, attrtype: 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(list: &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};
327

source code of linux/net/netfilter/nf_conntrack_proto_gre.c