1 /* Helper handling for netfilter. */
2 
3 /* (C) 1999-2001 Paul `Rusty' Russell
4  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
5  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
6  *
7  * This program is free software; you can redistribute it and/or modify
8  * it under the terms of the GNU General Public License version 2 as
9  * published by the Free Software Foundation.
10  */
11 
12 #include <linux/types.h>
13 #include <linux/netfilter.h>
14 #include <linux/module.h>
15 #include <linux/skbuff.h>
16 #include <linux/vmalloc.h>
17 #include <linux/stddef.h>
18 #include <linux/random.h>
19 #include <linux/err.h>
20 #include <linux/kernel.h>
21 #include <linux/netdevice.h>
22 #include <linux/rculist.h>
23 #include <linux/rtnetlink.h>
24 
25 #include <net/netfilter/nf_conntrack.h>
26 #include <net/netfilter/nf_conntrack_l3proto.h>
27 #include <net/netfilter/nf_conntrack_l4proto.h>
28 #include <net/netfilter/nf_conntrack_helper.h>
29 #include <net/netfilter/nf_conntrack_core.h>
30 #include <net/netfilter/nf_conntrack_extend.h>
31 
32 static DEFINE_MUTEX(nf_ct_helper_mutex);
33 static struct hlist_head *nf_ct_helper_hash __read_mostly;
34 static unsigned int nf_ct_helper_hsize __read_mostly;
35 static unsigned int nf_ct_helper_count __read_mostly;
36 
37 
38 /* Stupid hash, but collision free for the default registrations of the
39  * helpers currently in the kernel. */
helper_hash(const struct nf_conntrack_tuple * tuple)40 static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
41 {
42 	return (((tuple->src.l3num << 8) | tuple->dst.protonum) ^
43 		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
44 }
45 
46 static struct nf_conntrack_helper *
__nf_ct_helper_find(const struct nf_conntrack_tuple * tuple)47 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
48 {
49 	struct nf_conntrack_helper *helper;
50 	struct nf_conntrack_tuple_mask mask = { .src.u.all = htons(0xFFFF) };
51 	struct hlist_node *n;
52 	unsigned int h;
53 
54 	if (!nf_ct_helper_count)
55 		return NULL;
56 
57 	h = helper_hash(tuple);
58 	hlist_for_each_entry_rcu(helper, n, &nf_ct_helper_hash[h], hnode) {
59 		if (nf_ct_tuple_src_mask_cmp(tuple, &helper->tuple, &mask))
60 			return helper;
61 	}
62 	return NULL;
63 }
64 
65 struct nf_conntrack_helper *
__nf_conntrack_helper_find(const char * name,u16 l3num,u8 protonum)66 __nf_conntrack_helper_find(const char *name, u16 l3num, u8 protonum)
67 {
68 	struct nf_conntrack_helper *h;
69 	struct hlist_node *n;
70 	unsigned int i;
71 
72 	for (i = 0; i < nf_ct_helper_hsize; i++) {
73 		hlist_for_each_entry_rcu(h, n, &nf_ct_helper_hash[i], hnode) {
74 			if (!strcmp(h->name, name) &&
75 			    h->tuple.src.l3num == l3num &&
76 			    h->tuple.dst.protonum == protonum)
77 				return h;
78 		}
79 	}
80 	return NULL;
81 }
82 EXPORT_SYMBOL_GPL(__nf_conntrack_helper_find);
83 
84 struct nf_conntrack_helper *
nf_conntrack_helper_try_module_get(const char * name,u16 l3num,u8 protonum)85 nf_conntrack_helper_try_module_get(const char *name, u16 l3num, u8 protonum)
86 {
87 	struct nf_conntrack_helper *h;
88 
89 	h = __nf_conntrack_helper_find(name, l3num, protonum);
90 #ifdef CONFIG_MODULES
91 	if (h == NULL) {
92 		if (request_module("nfct-helper-%s", name) == 0)
93 			h = __nf_conntrack_helper_find(name, l3num, protonum);
94 	}
95 #endif
96 	if (h != NULL && !try_module_get(h->me))
97 		h = NULL;
98 
99 	return h;
100 }
101 EXPORT_SYMBOL_GPL(nf_conntrack_helper_try_module_get);
102 
nf_ct_helper_ext_add(struct nf_conn * ct,gfp_t gfp)103 struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
104 {
105 	struct nf_conn_help *help;
106 
107 	help = nf_ct_ext_add(ct, NF_CT_EXT_HELPER, gfp);
108 	if (help)
109 		INIT_HLIST_HEAD(&help->expectations);
110 	else
111 		pr_debug("failed to add helper extension area");
112 	return help;
113 }
114 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
115 
__nf_ct_try_assign_helper(struct nf_conn * ct,struct nf_conn * tmpl,gfp_t flags)116 int __nf_ct_try_assign_helper(struct nf_conn *ct, struct nf_conn *tmpl,
117 			      gfp_t flags)
118 {
119 	struct nf_conntrack_helper *helper = NULL;
120 	struct nf_conn_help *help;
121 	int ret = 0;
122 
123 	if (tmpl != NULL) {
124 		help = nfct_help(tmpl);
125 		if (help != NULL)
126 			helper = help->helper;
127 	}
128 
129 	help = nfct_help(ct);
130 	if (helper == NULL)
131 		helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
132 	if (helper == NULL) {
133 		if (help)
134 			rcu_assign_pointer(help->helper, NULL);
135 		goto out;
136 	}
137 
138 	if (help == NULL) {
139 		help = nf_ct_helper_ext_add(ct, flags);
140 		if (help == NULL) {
141 			ret = -ENOMEM;
142 			goto out;
143 		}
144 	} else {
145 		memset(&help->help, 0, sizeof(help->help));
146 	}
147 
148 	rcu_assign_pointer(help->helper, helper);
149 out:
150 	return ret;
151 }
152 EXPORT_SYMBOL_GPL(__nf_ct_try_assign_helper);
153 
unhelp(struct nf_conntrack_tuple_hash * i,const struct nf_conntrack_helper * me)154 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
155 			 const struct nf_conntrack_helper *me)
156 {
157 	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(i);
158 	struct nf_conn_help *help = nfct_help(ct);
159 
160 	if (help && rcu_dereference_protected(
161 			help->helper,
162 			lockdep_is_held(&nf_conntrack_lock)
163 			) == me) {
164 		nf_conntrack_event(IPCT_HELPER, ct);
165 		rcu_assign_pointer(help->helper, NULL);
166 	}
167 	return 0;
168 }
169 
nf_ct_helper_destroy(struct nf_conn * ct)170 void nf_ct_helper_destroy(struct nf_conn *ct)
171 {
172 	struct nf_conn_help *help = nfct_help(ct);
173 	struct nf_conntrack_helper *helper;
174 
175 	if (help) {
176 		rcu_read_lock();
177 		helper = rcu_dereference(help->helper);
178 		if (helper && helper->destroy)
179 			helper->destroy(ct);
180 		rcu_read_unlock();
181 	}
182 }
183 
nf_conntrack_helper_register(struct nf_conntrack_helper * me)184 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
185 {
186 	unsigned int h = helper_hash(&me->tuple);
187 
188 	BUG_ON(me->expect_policy == NULL);
189 	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
190 	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
191 
192 	mutex_lock(&nf_ct_helper_mutex);
193 	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);
194 	nf_ct_helper_count++;
195 	mutex_unlock(&nf_ct_helper_mutex);
196 
197 	return 0;
198 }
199 EXPORT_SYMBOL_GPL(nf_conntrack_helper_register);
200 
__nf_conntrack_helper_unregister(struct nf_conntrack_helper * me,struct net * net)201 static void __nf_conntrack_helper_unregister(struct nf_conntrack_helper *me,
202 					     struct net *net)
203 {
204 	struct nf_conntrack_tuple_hash *h;
205 	struct nf_conntrack_expect *exp;
206 	const struct hlist_node *n, *next;
207 	const struct hlist_nulls_node *nn;
208 	unsigned int i;
209 
210 	/* Get rid of expectations */
211 	for (i = 0; i < nf_ct_expect_hsize; i++) {
212 		hlist_for_each_entry_safe(exp, n, next,
213 					  &net->ct.expect_hash[i], hnode) {
214 			struct nf_conn_help *help = nfct_help(exp->master);
215 			if ((rcu_dereference_protected(
216 					help->helper,
217 					lockdep_is_held(&nf_conntrack_lock)
218 					) == me || exp->helper == me) &&
219 			    del_timer(&exp->timeout)) {
220 				nf_ct_unlink_expect(exp);
221 				nf_ct_expect_put(exp);
222 			}
223 		}
224 	}
225 
226 	/* Get rid of expecteds, set helpers to NULL. */
227 	hlist_nulls_for_each_entry(h, nn, &net->ct.unconfirmed, hnnode)
228 		unhelp(h, me);
229 	for (i = 0; i < net->ct.htable_size; i++) {
230 		hlist_nulls_for_each_entry(h, nn, &net->ct.hash[i], hnnode)
231 			unhelp(h, me);
232 	}
233 }
234 
nf_conntrack_helper_unregister(struct nf_conntrack_helper * me)235 void nf_conntrack_helper_unregister(struct nf_conntrack_helper *me)
236 {
237 	struct net *net;
238 
239 	mutex_lock(&nf_ct_helper_mutex);
240 	hlist_del_rcu(&me->hnode);
241 	nf_ct_helper_count--;
242 	mutex_unlock(&nf_ct_helper_mutex);
243 
244 	/* Make sure every nothing is still using the helper unless its a
245 	 * connection in the hash.
246 	 */
247 	synchronize_rcu();
248 
249 	rtnl_lock();
250 	spin_lock_bh(&nf_conntrack_lock);
251 	for_each_net(net)
252 		__nf_conntrack_helper_unregister(me, net);
253 	spin_unlock_bh(&nf_conntrack_lock);
254 	rtnl_unlock();
255 }
256 EXPORT_SYMBOL_GPL(nf_conntrack_helper_unregister);
257 
258 static struct nf_ct_ext_type helper_extend __read_mostly = {
259 	.len	= sizeof(struct nf_conn_help),
260 	.align	= __alignof__(struct nf_conn_help),
261 	.id	= NF_CT_EXT_HELPER,
262 };
263 
nf_conntrack_helper_init(void)264 int nf_conntrack_helper_init(void)
265 {
266 	int err;
267 
268 	nf_ct_helper_hsize = 1; /* gets rounded up to use one page */
269 	nf_ct_helper_hash = nf_ct_alloc_hashtable(&nf_ct_helper_hsize, 0);
270 	if (!nf_ct_helper_hash)
271 		return -ENOMEM;
272 
273 	err = nf_ct_extend_register(&helper_extend);
274 	if (err < 0)
275 		goto err1;
276 
277 	return 0;
278 
279 err1:
280 	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
281 	return err;
282 }
283 
nf_conntrack_helper_fini(void)284 void nf_conntrack_helper_fini(void)
285 {
286 	nf_ct_extend_unregister(&helper_extend);
287 	nf_ct_free_hashtable(nf_ct_helper_hash, nf_ct_helper_hsize);
288 }
289