xref: /linux/net/netfilter/nfnetlink.c (revision 14b42963f64b98ab61fa9723c03d71aa5ef4f862) 
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/sched.h>
23 #include <linux/timer.h>
24 #include <linux/string.h>
25 #include <linux/sockios.h>
26 #include <linux/net.h>
27 #include <linux/fcntl.h>
28 #include <linux/skbuff.h>
29 #include <asm/uaccess.h>
30 #include <asm/system.h>
31 #include <net/sock.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 
35 #include <linux/netfilter.h>
36 #include <linux/netlink.h>
37 #include <linux/netfilter/nfnetlink.h>
38 
39 MODULE_LICENSE("GPL");
40 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
41 MODULE_ALIAS_NET_PF_PROTO(PF_NETLINK, NETLINK_NETFILTER);
42 
43 static char __initdata nfversion[] = "0.30";
44 
45 #if 0
46 #define DEBUGP(format, args...)	\
47 		printk(KERN_DEBUG "%s(%d):%s(): " format, __FILE__, \
48 			__LINE__, __FUNCTION__, ## args)
49 #else
50 #define DEBUGP(format, args...)
51 #endif
52 
53 static struct sock *nfnl = NULL;
54 static struct nfnetlink_subsystem *subsys_table[NFNL_SUBSYS_COUNT];
55 DECLARE_MUTEX(nfnl_sem);
56 
57 void nfnl_lock(void)
58 {
59 	nfnl_shlock();
60 }
61 
62 void nfnl_unlock(void)
63 {
64 	nfnl_shunlock();
65 }
66 
67 int nfnetlink_subsys_register(struct nfnetlink_subsystem *n)
68 {
69 	DEBUGP("registering subsystem ID %u\n", n->subsys_id);
70 
71 	nfnl_lock();
72 	if (subsys_table[n->subsys_id]) {
73 		nfnl_unlock();
74 		return -EBUSY;
75 	}
76 	subsys_table[n->subsys_id] = n;
77 	nfnl_unlock();
78 
79 	return 0;
80 }
81 
82 int nfnetlink_subsys_unregister(struct nfnetlink_subsystem *n)
83 {
84 	DEBUGP("unregistering subsystem ID %u\n", n->subsys_id);
85 
86 	nfnl_lock();
87 	subsys_table[n->subsys_id] = NULL;
88 	nfnl_unlock();
89 
90 	return 0;
91 }
92 
93 static inline struct nfnetlink_subsystem *nfnetlink_get_subsys(u_int16_t type)
94 {
95 	u_int8_t subsys_id = NFNL_SUBSYS_ID(type);
96 
97 	if (subsys_id >= NFNL_SUBSYS_COUNT
98 	    || subsys_table[subsys_id] == NULL)
99 		return NULL;
100 
101 	return subsys_table[subsys_id];
102 }
103 
104 static inline struct nfnl_callback *
105 nfnetlink_find_client(u_int16_t type, struct nfnetlink_subsystem *ss)
106 {
107 	u_int8_t cb_id = NFNL_MSG_TYPE(type);
108 
109 	if (cb_id >= ss->cb_count) {
110 		DEBUGP("msgtype %u >= %u, returning\n", type, ss->cb_count);
111 		return NULL;
112 	}
113 
114 	return &ss->cb[cb_id];
115 }
116 
117 void __nfa_fill(struct sk_buff *skb, int attrtype, int attrlen,
118 		const void *data)
119 {
120 	struct nfattr *nfa;
121 	int size = NFA_LENGTH(attrlen);
122 
123 	nfa = (struct nfattr *)skb_put(skb, NFA_ALIGN(size));
124 	nfa->nfa_type = attrtype;
125 	nfa->nfa_len  = size;
126 	memcpy(NFA_DATA(nfa), data, attrlen);
127 	memset(NFA_DATA(nfa) + attrlen, 0, NFA_ALIGN(size) - size);
128 }
129 
130 void nfattr_parse(struct nfattr *tb[], int maxattr, struct nfattr *nfa, int len)
131 {
132 	memset(tb, 0, sizeof(struct nfattr *) * maxattr);
133 
134 	while (NFA_OK(nfa, len)) {
135 		unsigned flavor = NFA_TYPE(nfa);
136 		if (flavor && flavor <= maxattr)
137 			tb[flavor-1] = nfa;
138 		nfa = NFA_NEXT(nfa, len);
139 	}
140 }
141 
142 /**
143  * nfnetlink_check_attributes - check and parse nfnetlink attributes
144  *
145  * subsys: nfnl subsystem for which this message is to be parsed
146  * nlmsghdr: netlink message to be checked/parsed
147  * cda: array of pointers, needs to be at least subsys->attr_count big
148  *
149  */
150 static int
151 nfnetlink_check_attributes(struct nfnetlink_subsystem *subsys,
152 			   struct nlmsghdr *nlh, struct nfattr *cda[])
153 {
154 	int min_len;
155 	u_int16_t attr_count;
156 	u_int8_t cb_id = NFNL_MSG_TYPE(nlh->nlmsg_type);
157 
158 	if (unlikely(cb_id >= subsys->cb_count)) {
159 		DEBUGP("msgtype %u >= %u, returning\n",
160 			cb_id, subsys->cb_count);
161 		return -EINVAL;
162 	}
163 
164 	min_len = NLMSG_SPACE(sizeof(struct nfgenmsg));
165 	if (unlikely(nlh->nlmsg_len < min_len))
166 		return -EINVAL;
167 
168 	attr_count = subsys->cb[cb_id].attr_count;
169 	memset(cda, 0, sizeof(struct nfattr *) * attr_count);
170 
171 	/* check attribute lengths. */
172 	if (likely(nlh->nlmsg_len > min_len)) {
173 		struct nfattr *attr = NFM_NFA(NLMSG_DATA(nlh));
174 		int attrlen = nlh->nlmsg_len - NLMSG_ALIGN(min_len);
175 
176 		while (NFA_OK(attr, attrlen)) {
177 			unsigned flavor = NFA_TYPE(attr);
178 			if (flavor) {
179 				if (flavor > attr_count)
180 					return -EINVAL;
181 				cda[flavor - 1] = attr;
182 			}
183 			attr = NFA_NEXT(attr, attrlen);
184 		}
185 	}
186 
187 	/* implicit: if nlmsg_len == min_len, we return 0, and an empty
188 	 * (zeroed) cda[] array. The message is valid, but empty. */
189 
190         return 0;
191 }
192 
193 int nfnetlink_has_listeners(unsigned int group)
194 {
195 	return netlink_has_listeners(nfnl, group);
196 }
197 EXPORT_SYMBOL_GPL(nfnetlink_has_listeners);
198 
199 int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group, int echo)
200 {
201 	gfp_t allocation = in_interrupt() ? GFP_ATOMIC : GFP_KERNEL;
202 	int err = 0;
203 
204 	NETLINK_CB(skb).dst_group = group;
205 	if (echo)
206 		atomic_inc(&skb->users);
207 	netlink_broadcast(nfnl, skb, pid, group, allocation);
208 	if (echo)
209 		err = netlink_unicast(nfnl, skb, pid, MSG_DONTWAIT);
210 
211 	return err;
212 }
213 
214 int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags)
215 {
216 	return netlink_unicast(nfnl, skb, pid, flags);
217 }
218 
219 /* Process one complete nfnetlink message. */
220 static int nfnetlink_rcv_msg(struct sk_buff *skb,
221 				    struct nlmsghdr *nlh, int *errp)
222 {
223 	struct nfnl_callback *nc;
224 	struct nfnetlink_subsystem *ss;
225 	int type, err = 0;
226 
227 	DEBUGP("entered; subsys=%u, msgtype=%u\n",
228 		 NFNL_SUBSYS_ID(nlh->nlmsg_type),
229 		 NFNL_MSG_TYPE(nlh->nlmsg_type));
230 
231 	if (security_netlink_recv(skb, CAP_NET_ADMIN)) {
232 		DEBUGP("missing CAP_NET_ADMIN\n");
233 		*errp = -EPERM;
234 		return -1;
235 	}
236 
237 	/* Only requests are handled by kernel now. */
238 	if (!(nlh->nlmsg_flags & NLM_F_REQUEST)) {
239 		DEBUGP("received non-request message\n");
240 		return 0;
241 	}
242 
243 	/* All the messages must at least contain nfgenmsg */
244 	if (nlh->nlmsg_len < NLMSG_SPACE(sizeof(struct nfgenmsg))) {
245 		DEBUGP("received message was too short\n");
246 		return 0;
247 	}
248 
249 	type = nlh->nlmsg_type;
250 	ss = nfnetlink_get_subsys(type);
251 	if (!ss) {
252 #ifdef CONFIG_KMOD
253 		/* don't call nfnl_shunlock, since it would reenter
254 		 * with further packet processing */
255 		up(&nfnl_sem);
256 		request_module("nfnetlink-subsys-%d", NFNL_SUBSYS_ID(type));
257 		nfnl_shlock();
258 		ss = nfnetlink_get_subsys(type);
259 		if (!ss)
260 #endif
261 			goto err_inval;
262 	}
263 
264 	nc = nfnetlink_find_client(type, ss);
265 	if (!nc) {
266 		DEBUGP("unable to find client for type %d\n", type);
267 		goto err_inval;
268 	}
269 
270 	{
271 		u_int16_t attr_count =
272 			ss->cb[NFNL_MSG_TYPE(nlh->nlmsg_type)].attr_count;
273 		struct nfattr *cda[attr_count];
274 
275 		memset(cda, 0, sizeof(struct nfattr *) * attr_count);
276 
277 		err = nfnetlink_check_attributes(ss, nlh, cda);
278 		if (err < 0)
279 			goto err_inval;
280 
281 		DEBUGP("calling handler\n");
282 		err = nc->call(nfnl, skb, nlh, cda, errp);
283 		*errp = err;
284 		return err;
285 	}
286 
287 err_inval:
288 	DEBUGP("returning -EINVAL\n");
289 	*errp = -EINVAL;
290 	return -1;
291 }
292 
293 /* Process one packet of messages. */
294 static inline int nfnetlink_rcv_skb(struct sk_buff *skb)
295 {
296 	int err;
297 	struct nlmsghdr *nlh;
298 
299 	while (skb->len >= NLMSG_SPACE(0)) {
300 		u32 rlen;
301 
302 		nlh = (struct nlmsghdr *)skb->data;
303 		if (nlh->nlmsg_len < sizeof(struct nlmsghdr)
304 		    || skb->len < nlh->nlmsg_len)
305 			return 0;
306 		rlen = NLMSG_ALIGN(nlh->nlmsg_len);
307 		if (rlen > skb->len)
308 			rlen = skb->len;
309 		if (nfnetlink_rcv_msg(skb, nlh, &err)) {
310 			if (!err)
311 				return -1;
312 			netlink_ack(skb, nlh, err);
313 		} else
314 			if (nlh->nlmsg_flags & NLM_F_ACK)
315 				netlink_ack(skb, nlh, 0);
316 		skb_pull(skb, rlen);
317 	}
318 
319 	return 0;
320 }
321 
322 static void nfnetlink_rcv(struct sock *sk, int len)
323 {
324 	do {
325 		struct sk_buff *skb;
326 
327 		if (nfnl_shlock_nowait())
328 			return;
329 
330 		while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {
331 			if (nfnetlink_rcv_skb(skb)) {
332 				if (skb->len)
333 					skb_queue_head(&sk->sk_receive_queue,
334 						       skb);
335 				else
336 					kfree_skb(skb);
337 				break;
338 			}
339 			kfree_skb(skb);
340 		}
341 
342 		/* don't call nfnl_shunlock, since it would reenter
343 		 * with further packet processing */
344 		up(&nfnl_sem);
345 	} while(nfnl && nfnl->sk_receive_queue.qlen);
346 }
347 
348 static void __exit nfnetlink_exit(void)
349 {
350 	printk("Removing netfilter NETLINK layer.\n");
351 	sock_release(nfnl->sk_socket);
352 	return;
353 }
354 
355 static int __init nfnetlink_init(void)
356 {
357 	printk("Netfilter messages via NETLINK v%s.\n", nfversion);
358 
359 	nfnl = netlink_kernel_create(NETLINK_NETFILTER, NFNLGRP_MAX,
360 	                             nfnetlink_rcv, THIS_MODULE);
361 	if (!nfnl) {
362 		printk(KERN_ERR "cannot initialize nfnetlink!\n");
363 		return -1;
364 	}
365 
366 	return 0;
367 }
368 
369 module_init(nfnetlink_init);
370 module_exit(nfnetlink_exit);
371 
372 EXPORT_SYMBOL_GPL(nfnetlink_subsys_register);
373 EXPORT_SYMBOL_GPL(nfnetlink_subsys_unregister);
374 EXPORT_SYMBOL_GPL(nfnetlink_send);
375 EXPORT_SYMBOL_GPL(nfnetlink_unicast);
376 EXPORT_SYMBOL_GPL(nfattr_parse);
377 EXPORT_SYMBOL_GPL(__nfa_fill);
378