xref: /linux/net/netfilter/nfnetlink.c (revision c537b994505099b7197e7d3125b942ecbcc51eb6) 
1 /* Netfilter messages via netlink socket. Allows for user space
2  * protocol helpers and general trouble making from userspace.
3  *
4  * (C) 2001 by Jay Schulist <jschlst@samba.org>,
5  * (C) 2002-2005 by Harald Welte <laforge@gnumonks.org>
6  * (C) 2005 by Pablo Neira Ayuso <pablo@eurodev.net>
7  *
8  * Initial netfilter messages via netlink development funded and
9  * generally made possible by Network Robots, Inc. (www.networkrobots.com)
10  *
11  * Further development of this code funded by Astaro AG (http://www.astaro.com)
12  *
13  * This software may be used and distributed according to the terms
14  * of the GNU General Public License, incorporated herein by reference.
15  */
16 
17 #include <linux/module.h>
18 #include <linux/types.h>
19 #include <linux/socket.h>
20 #include <linux/kernel.h>
21 #include <linux/major.h>
22 #include <linux/timer.h>
23 #include <linux/string.h>
24 #include <linux/sockios.h>
25 #include <linux/net.h>
26 #include <linux/fcntl.h>
27 #include <linux/skbuff.h>
28 #include <asm/uaccess.h>
29 #include <asm/system.h>
30 #include <net/sock.h>
31 #include <linux/init.h>
32 #include <linux/spinlock.h>
33 
34 #include <linux/netfilter.h>
35 #include <linux/netlink.h>
36 #include <linux/netfilter/nfnetlink.h>
37 
38 MODULE_LICENSE("GPL");
39 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
40 MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
41 
42 static char __initdata nfversion[] = "0.30";
43 
44 #if 0
45 #define DEBUGP(format, args...)	\
46 		printk(KERN_DEBUG "%s(%d):%s(): " format, __FILE__, \
47 			__LINE__, __FUNCTION__, ## args)
48 #else
49 #define DEBUGP(format, args...)
50 #endif
51 
52 static struct sock *nfnl = NULL;
53 static struct nfnetlink_subsystem *subsys_table[NFNL_SUBSYS_COUNT];
54 DECLARE_MUTEX(nfnl_sem);
55 
56 void nfnl_lock(void)
57 {
58 	nfnl_shlock();
59 }
60 
61 void nfnl_unlock(void)
62 {
63 	nfnl_shunlock();
64 }
65 
66 int nfnetlink_subsys_register(struct nfnetlink_subsystem *n)
67 {
68 	DEBUGP("registering subsystem ID %u\n", n->subsys_id);
69 
70 	nfnl_lock();
71 	if (subsys_table[n->subsys_id]) {
72 		nfnl_unlock();
73 		return -EBUSY;
74 	}
75 	subsys_table[n->subsys_id] = n;
76 	nfnl_unlock();
77 
78 	return 0;
79 }
80 
81 int nfnetlink_subsys_unregister(struct nfnetlink_subsystem *n)
82 {
83 	DEBUGP("unregistering subsystem ID %u\n", n->subsys_id);
84 
85 	nfnl_lock();
86 	subsys_table[n->subsys_id] = NULL;
87 	nfnl_unlock();
88 
89 	return 0;
90 }
91 
92 static inline struct nfnetlink_subsystem *nfnetlink_get_subsys(u_int16_t type)
93 {
94 	u_int8_t subsys_id = NFNL_SUBSYS_ID(type);
95 
96 	if (subsys_id >= NFNL_SUBSYS_COUNT
97 	    || subsys_table[subsys_id] == NULL)
98 		return NULL;
99 
100 	return subsys_table[subsys_id];
101 }
102 
103 static inline struct nfnl_callback *
104 nfnetlink_find_client(u_int16_t type, struct nfnetlink_subsystem *ss)
105 {
106 	u_int8_t cb_id = NFNL_MSG_TYPE(type);
107 
108 	if (cb_id >= ss->cb_count) {
109 		DEBUGP("msgtype %u >= %u, returning\n", type, ss->cb_count);
110 		return NULL;
111 	}
112 
113 	return &ss->cb[cb_id];
114 }
115 
116 void __nfa_fill(struct sk_buff *skb, int attrtype, int attrlen,
117 		const void *data)
118 {
119 	struct nfattr *nfa;
120 	int size = NFA_LENGTH(attrlen);
121 
122 	nfa = (struct nfattr *)skb_put(skb, NFA_ALIGN(size));
123 	nfa->nfa_type = attrtype;
124 	nfa->nfa_len  = size;
125 	memcpy(NFA_DATA(nfa), data, attrlen);
126 	memset(NFA_DATA(nfa) + attrlen, 0, NFA_ALIGN(size) - size);
127 }
128 
129 void nfattr_parse(struct nfattr *tb[], int maxattr, struct nfattr *nfa, int len)
130 {
131 	memset(tb, 0, sizeof(struct nfattr *) * maxattr);
132 
133 	while (NFA_OK(nfa, len)) {
134 		unsigned flavor = NFA_TYPE(nfa);
135 		if (flavor && flavor <= maxattr)
136 			tb[flavor-1] = nfa;
137 		nfa = NFA_NEXT(nfa, len);
138 	}
139 }
140 
141 /**
142  * nfnetlink_check_attributes - check and parse nfnetlink attributes
143  *
144  * subsys: nfnl subsystem for which this message is to be parsed
145  * nlmsghdr: netlink message to be checked/parsed
146  * cda: array of pointers, needs to be at least subsys->attr_count big
147  *
148  */
149 static int
150 nfnetlink_check_attributes(struct nfnetlink_subsystem *subsys,
151 			   struct nlmsghdr *nlh, struct nfattr *cda[])
152 {
153 	int min_len;
154 	u_int16_t attr_count;
155 	u_int8_t cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
156 
157 	if (unlikely(cb_id >= subsys->cb_count)) {
158 		DEBUGP("msgtype %u >= %u, returning\n",
159 			cb_id, subsys->cb_count);
160 		return -EINVAL;
161 	}
162 
163 	min_len = NLMSG_SPACE(sizeof(struct nfgenmsg));
164 	if (unlikely(nlh->nlmsg_len < min_len))
165 		return -EINVAL;
166 
167 	attr_count = subsys->cb[cb_id].attr_count;
168 	memset(cda, 0, sizeof(struct nfattr *) * attr_count);
169 
170 	/* check attribute lengths. */
171 	if (likely(nlh->nlmsg_len > min_len)) {
172 		struct nfattr *attr = NFM_NFA(NLMSG_DATA(nlh));
173 		int attrlen = nlh->nlmsg_len - NLMSG_ALIGN(min_len);
174 
175 		while (NFA_OK(attr, attrlen)) {
176 			unsigned flavor = NFA_TYPE(attr);
177 			if (flavor) {
178 				if (flavor > attr_count)
179 					return -EINVAL;
180 				cda[flavor - 1] = attr;
181 			}
182 			attr = NFA_NEXT(attr, attrlen);
183 		}
184 	}
185 
186 	/* implicit: if nlmsg_len == min_len, we return 0, and an empty
187 	 * (zeroed) cda[] array. The message is valid, but empty. */
188 
189 	return 0;
190 }
191 
192 int nfnetlink_has_listeners(unsigned int group)
193 {
194 	return netlink_has_listeners(nfnl, group);
195 }
196 EXPORT_SYMBOL_GPL(nfnetlink_has_listeners);
197 
198 int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, int echo)
199 {
200 	int err = 0;
201 
202 	NETLINK_CB(skb).dst_group = group;
203 	if (echo)
204 		atomic_inc(&skb->users);
205 	netlink_broadcast(nfnl, skb, pid, group, gfp_any());
206 	if (echo)
207 		err = netlink_unicast(nfnl, skb, pid, MSG_DONTWAIT);
208 
209 	return err;
210 }
211 
212 int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags)
213 {
214 	return netlink_unicast(nfnl, skb, pid, flags);
215 }
216 
217 /* Process one complete nfnetlink message. */
218 static int nfnetlink_rcv_msg(struct sk_buff *skb,
219 				    struct nlmsghdr *nlh, int *errp)
220 {
221 	struct nfnl_callback *nc;
222 	struct nfnetlink_subsystem *ss;
223 	int type, err = 0;
224 
225 	DEBUGP("entered; subsys=%u, msgtype=%u\n",
226 		 NFNL_SUBSYS_ID(nlh->nlmsg_type),
227 		 NFNL_MSG_TYPE(nlh->nlmsg_type));
228 
229 	if (security_netlink_recv(skb, CAP_NET_ADMIN)) {
230 		DEBUGP("missing CAP_NET_ADMIN\n");
231 		*errp = -EPERM;
232 		return -1;
233 	}
234 
235 	/* Only requests are handled by kernel now. */
236 	if (!(nlh->nlmsg_flags & NLM_F_REQUEST)) {
237 		DEBUGP("received non-request message\n");
238 		return 0;
239 	}
240 
241 	/* All the messages must at least contain nfgenmsg */
242 	if (nlh->nlmsg_len < NLMSG_SPACE(sizeof(struct nfgenmsg))) {
243 		DEBUGP("received message was too short\n");
244 		return 0;
245 	}
246 
247 	type = nlh->nlmsg_type;
248 	ss = nfnetlink_get_subsys(type);
249 	if (!ss) {
250 #ifdef CONFIG_KMOD
251 		/* don't call nfnl_shunlock, since it would reenter
252 		 * with further packet processing */
253 		up(&nfnl_sem);
254 		request_module("nfnetlink-subsys-%d", NFNL_SUBSYS_ID(type));
255 		nfnl_shlock();
256 		ss = nfnetlink_get_subsys(type);
257 		if (!ss)
258 #endif
259 			goto err_inval;
260 	}
261 
262 	nc = nfnetlink_find_client(type, ss);
263 	if (!nc) {
264 		DEBUGP("unable to find client for type %d\n", type);
265 		goto err_inval;
266 	}
267 
268 	{
269 		u_int16_t attr_count =
270 			ss->cb[NFNL_MSG_TYPE(nlh->nlmsg_type)].attr_count;
271 		struct nfattr *cda[attr_count];
272 
273 		memset(cda, 0, sizeof(struct nfattr *) * attr_count);
274 
275 		err = nfnetlink_check_attributes(ss, nlh, cda);
276 		if (err < 0)
277 			goto err_inval;
278 
279 		DEBUGP("calling handler\n");
280 		err = nc->call(nfnl, skb, nlh, cda, errp);
281 		*errp = err;
282 		return err;
283 	}
284 
285 err_inval:
286 	DEBUGP("returning -EINVAL\n");
287 	*errp = -EINVAL;
288 	return -1;
289 }
290 
291 /* Process one packet of messages. */
292 static inline int nfnetlink_rcv_skb(struct sk_buff *skb)
293 {
294 	int err;
295 	struct nlmsghdr *nlh;
296 
297 	while (skb->len >= NLMSG_SPACE(0)) {
298 		u32 rlen;
299 
300 		nlh = (struct nlmsghdr *)skb->data;
301 		if (nlh->nlmsg_len < sizeof(struct nlmsghdr)
302 		    || skb->len < nlh->nlmsg_len)
303 			return 0;
304 		rlen = NLMSG_ALIGN(nlh->nlmsg_len);
305 		if (rlen > skb->len)
306 			rlen = skb->len;
307 		if (nfnetlink_rcv_msg(skb, nlh, &err)) {
308 			if (!err)
309 				return -1;
310 			netlink_ack(skb, nlh, err);
311 		} else
312 			if (nlh->nlmsg_flags & NLM_F_ACK)
313 				netlink_ack(skb, nlh, 0);
314 		skb_pull(skb, rlen);
315 	}
316 
317 	return 0;
318 }
319 
320 static void nfnetlink_rcv(struct sock *sk, int len)
321 {
322 	do {
323 		struct sk_buff *skb;
324 
325 		if (nfnl_shlock_nowait())
326 			return;
327 
328 		while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {
329 			if (nfnetlink_rcv_skb(skb)) {
330 				if (skb->len)
331 					skb_queue_head(&sk->sk_receive_queue,
332 						       skb);
333 				else
334 					kfree_skb(skb);
335 				break;
336 			}
337 			kfree_skb(skb);
338 		}
339 
340 		/* don't call nfnl_shunlock, since it would reenter
341 		 * with further packet processing */
342 		up(&nfnl_sem);
343 	} while(nfnl && nfnl->sk_receive_queue.qlen);
344 }
345 
346 static void __exit nfnetlink_exit(void)
347 {
348 	printk("Removing netfilter NETLINK layer.\n");
349 	sock_release(nfnl->sk_socket);
350 	return;
351 }
352 
353 static int __init nfnetlink_init(void)
354 {
355 	printk("Netfilter messages via NETLINK v%s.\n", nfversion);
356 
357 	nfnl = netlink_kernel_create(NETLINK_NETFILTER, NFNLGRP_MAX,
358 				     nfnetlink_rcv, THIS_MODULE);
359 	if (!nfnl) {
360 		printk(KERN_ERR "cannot initialize nfnetlink!\n");
361 		return -1;
362 	}
363 
364 	return 0;
365 }
366 
367 module_init(nfnetlink_init);
368 module_exit(nfnetlink_exit);
369 
370 EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);
371 EXPORT_SYMBOL_GPL(nfnetlink_subsys_unregister);
372 EXPORT_SYMBOL_GPL(nfnetlink_send);
373 EXPORT_SYMBOL_GPL(nfnetlink_unicast);
374 EXPORT_SYMBOL_GPL(nfattr_parse);
375 EXPORT_SYMBOL_GPL(__nfa_fill);
376