xref: /openbmc/linux/net/netfilter/xt_connlimit.c (revision 23c2b932) 
1 /*
2  * netfilter module to limit the number of parallel tcp
3  * connections per IP address.
4  *   (c) 2000 Gerd Knorr <kraxel@bytesex.org>
5  *   Nov 2002: Martin Bene <martin.bene@icomedias.com>:
6  *		only ignore TIME_WAIT or gone connections
7  *   (C) CC Computer Consultants GmbH, 2007
8  *
9  * based on ...
10  *
11  * Kernel module to match connection tracking information.
12  * GPL (C) 1999  Rusty Russell (rusty@rustcorp.com.au).
13  */
14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
15 #include <linux/in.h>
16 #include <linux/in6.h>
17 #include <linux/ip.h>
18 #include <linux/ipv6.h>
19 #include <linux/jhash.h>
20 #include <linux/slab.h>
21 #include <linux/list.h>
22 #include <linux/rbtree.h>
23 #include <linux/module.h>
24 #include <linux/random.h>
25 #include <linux/skbuff.h>
26 #include <linux/spinlock.h>
27 #include <linux/netfilter/nf_conntrack_tcp.h>
28 #include <linux/netfilter/x_tables.h>
29 #include <linux/netfilter/xt_connlimit.h>
30 #include <net/netfilter/nf_conntrack.h>
31 #include <net/netfilter/nf_conntrack_core.h>
32 #include <net/netfilter/nf_conntrack_tuple.h>
33 #include <net/netfilter/nf_conntrack_zones.h>
34 
35 #define CONNLIMIT_SLOTS		256U
36 
37 #ifdef CONFIG_LOCKDEP
38 #define CONNLIMIT_LOCK_SLOTS	8U
39 #else
40 #define CONNLIMIT_LOCK_SLOTS	256U
41 #endif
42 
43 #define CONNLIMIT_GC_MAX_NODES	8
44 
45 /* we will save the tuples of all connections we care about */
46 struct xt_connlimit_conn {
47 	struct hlist_node		node;
48 	struct nf_conntrack_tuple	tuple;
49 	union nf_inet_addr		addr;
50 };
51 
52 struct xt_connlimit_rb {
53 	struct rb_node node;
54 	struct hlist_head hhead; /* connections/hosts in same subnet */
55 	union nf_inet_addr addr; /* search key */
56 };
57 
58 static spinlock_t xt_connlimit_locks[CONNLIMIT_LOCK_SLOTS] __cacheline_aligned_in_smp;
59 
60 struct xt_connlimit_data {
61 	struct rb_root climit_root4[CONNLIMIT_SLOTS];
62 	struct rb_root climit_root6[CONNLIMIT_SLOTS];
63 };
64 
65 static u_int32_t connlimit_rnd __read_mostly;
66 static struct kmem_cache *connlimit_rb_cachep __read_mostly;
67 static struct kmem_cache *connlimit_conn_cachep __read_mostly;
68 
69 static inline unsigned int connlimit_iphash(__be32 addr)
70 {
71 	return jhash_1word((__force __u32)addr,
72 			    connlimit_rnd) % CONNLIMIT_SLOTS;
73 }
74 
75 static inline unsigned int
76 connlimit_iphash6(const union nf_inet_addr *addr,
77                   const union nf_inet_addr *mask)
78 {
79 	union nf_inet_addr res;
80 	unsigned int i;
81 
82 	for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
83 		res.ip6[i] = addr->ip6[i] & mask->ip6[i];
84 
85 	return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6),
86 		       connlimit_rnd) % CONNLIMIT_SLOTS;
87 }
88 
89 static inline bool already_closed(const struct nf_conn *conn)
90 {
91 	if (nf_ct_protonum(conn) == IPPROTO_TCP)
92 		return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
93 		       conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
94 	else
95 		return 0;
96 }
97 
98 static int
99 same_source_net(const union nf_inet_addr *addr,
100 		const union nf_inet_addr *mask,
101 		const union nf_inet_addr *u3, u_int8_t family)
102 {
103 	if (family == NFPROTO_IPV4) {
104 		return ntohl(addr->ip & mask->ip) -
105 		       ntohl(u3->ip & mask->ip);
106 	} else {
107 		union nf_inet_addr lh, rh;
108 		unsigned int i;
109 
110 		for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
111 			lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
112 			rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
113 		}
114 
115 		return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6));
116 	}
117 }
118 
119 static bool add_hlist(struct hlist_head *head,
120 		      const struct nf_conntrack_tuple *tuple,
121 		      const union nf_inet_addr *addr)
122 {
123 	struct xt_connlimit_conn *conn;
124 
125 	conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
126 	if (conn == NULL)
127 		return false;
128 	conn->tuple = *tuple;
129 	conn->addr = *addr;
130 	hlist_add_head(&conn->node, head);
131 	return true;
132 }
133 
134 static unsigned int check_hlist(struct net *net,
135 				struct hlist_head *head,
136 				const struct nf_conntrack_tuple *tuple,
137 				const struct nf_conntrack_zone *zone,
138 				bool *addit)
139 {
140 	const struct nf_conntrack_tuple_hash *found;
141 	struct xt_connlimit_conn *conn;
142 	struct hlist_node *n;
143 	struct nf_conn *found_ct;
144 	unsigned int length = 0;
145 
146 	*addit = true;
147 	rcu_read_lock();
148 
149 	/* check the saved connections */
150 	hlist_for_each_entry_safe(conn, n, head, node) {
151 		found = nf_conntrack_find_get(net, zone, &conn->tuple);
152 		if (found == NULL) {
153 			hlist_del(&conn->node);
154 			kmem_cache_free(connlimit_conn_cachep, conn);
155 			continue;
156 		}
157 
158 		found_ct = nf_ct_tuplehash_to_ctrack(found);
159 
160 		if (nf_ct_tuple_equal(&conn->tuple, tuple)) {
161 			/*
162 			 * Just to be sure we have it only once in the list.
163 			 * We should not see tuples twice unless someone hooks
164 			 * this into a table without "-p tcp --syn".
165 			 */
166 			*addit = false;
167 		} else if (already_closed(found_ct)) {
168 			/*
169 			 * we do not care about connections which are
170 			 * closed already -> ditch it
171 			 */
172 			nf_ct_put(found_ct);
173 			hlist_del(&conn->node);
174 			kmem_cache_free(connlimit_conn_cachep, conn);
175 			continue;
176 		}
177 
178 		nf_ct_put(found_ct);
179 		length++;
180 	}
181 
182 	rcu_read_unlock();
183 
184 	return length;
185 }
186 
187 static void tree_nodes_free(struct rb_root *root,
188 			    struct xt_connlimit_rb *gc_nodes[],
189 			    unsigned int gc_count)
190 {
191 	struct xt_connlimit_rb *rbconn;
192 
193 	while (gc_count) {
194 		rbconn = gc_nodes[--gc_count];
195 		rb_erase(&rbconn->node, root);
196 		kmem_cache_free(connlimit_rb_cachep, rbconn);
197 	}
198 }
199 
200 static unsigned int
201 count_tree(struct net *net, struct rb_root *root,
202 	   const struct nf_conntrack_tuple *tuple,
203 	   const union nf_inet_addr *addr, const union nf_inet_addr *mask,
204 	   u8 family, const struct nf_conntrack_zone *zone)
205 {
206 	struct xt_connlimit_rb *gc_nodes[CONNLIMIT_GC_MAX_NODES];
207 	struct rb_node **rbnode, *parent;
208 	struct xt_connlimit_rb *rbconn;
209 	struct xt_connlimit_conn *conn;
210 	unsigned int gc_count;
211 	bool no_gc = false;
212 
213  restart:
214 	gc_count = 0;
215 	parent = NULL;
216 	rbnode = &(root->rb_node);
217 	while (*rbnode) {
218 		int diff;
219 		bool addit;
220 
221 		rbconn = container_of(*rbnode, struct xt_connlimit_rb, node);
222 
223 		parent = *rbnode;
224 		diff = same_source_net(addr, mask, &rbconn->addr, family);
225 		if (diff < 0) {
226 			rbnode = &((*rbnode)->rb_left);
227 		} else if (diff > 0) {
228 			rbnode = &((*rbnode)->rb_right);
229 		} else {
230 			/* same source network -> be counted! */
231 			unsigned int count;
232 			count = check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
233 
234 			tree_nodes_free(root, gc_nodes, gc_count);
235 			if (!addit)
236 				return count;
237 
238 			if (!add_hlist(&rbconn->hhead, tuple, addr))
239 				return 0; /* hotdrop */
240 
241 			return count + 1;
242 		}
243 
244 		if (no_gc || gc_count >= ARRAY_SIZE(gc_nodes))
245 			continue;
246 
247 		/* only used for GC on hhead, retval and 'addit' ignored */
248 		check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
249 		if (hlist_empty(&rbconn->hhead))
250 			gc_nodes[gc_count++] = rbconn;
251 	}
252 
253 	if (gc_count) {
254 		no_gc = true;
255 		tree_nodes_free(root, gc_nodes, gc_count);
256 		/* tree_node_free before new allocation permits
257 		 * allocator to re-use newly free'd object.
258 		 *
259 		 * This is a rare event; in most cases we will find
260 		 * existing node to re-use. (or gc_count is 0).
261 		 */
262 		goto restart;
263 	}
264 
265 	/* no match, need to insert new node */
266 	rbconn = kmem_cache_alloc(connlimit_rb_cachep, GFP_ATOMIC);
267 	if (rbconn == NULL)
268 		return 0;
269 
270 	conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
271 	if (conn == NULL) {
272 		kmem_cache_free(connlimit_rb_cachep, rbconn);
273 		return 0;
274 	}
275 
276 	conn->tuple = *tuple;
277 	conn->addr = *addr;
278 	rbconn->addr = *addr;
279 
280 	INIT_HLIST_HEAD(&rbconn->hhead);
281 	hlist_add_head(&conn->node, &rbconn->hhead);
282 
283 	rb_link_node(&rbconn->node, parent, rbnode);
284 	rb_insert_color(&rbconn->node, root);
285 	return 1;
286 }
287 
288 static int count_them(struct net *net,
289 		      struct xt_connlimit_data *data,
290 		      const struct nf_conntrack_tuple *tuple,
291 		      const union nf_inet_addr *addr,
292 		      const union nf_inet_addr *mask,
293 		      u_int8_t family,
294 		      const struct nf_conntrack_zone *zone)
295 {
296 	struct rb_root *root;
297 	int count;
298 	u32 hash;
299 
300 	if (family == NFPROTO_IPV6) {
301 		hash = connlimit_iphash6(addr, mask);
302 		root = &data->climit_root6[hash];
303 	} else {
304 		hash = connlimit_iphash(addr->ip & mask->ip);
305 		root = &data->climit_root4[hash];
306 	}
307 
308 	spin_lock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
309 
310 	count = count_tree(net, root, tuple, addr, mask, family, zone);
311 
312 	spin_unlock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
313 
314 	return count;
315 }
316 
317 static bool
318 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
319 {
320 	struct net *net = par->net;
321 	const struct xt_connlimit_info *info = par->matchinfo;
322 	union nf_inet_addr addr;
323 	struct nf_conntrack_tuple tuple;
324 	const struct nf_conntrack_tuple *tuple_ptr = &tuple;
325 	const struct nf_conntrack_zone *zone = &nf_ct_zone_dflt;
326 	enum ip_conntrack_info ctinfo;
327 	const struct nf_conn *ct;
328 	unsigned int connections;
329 
330 	ct = nf_ct_get(skb, &ctinfo);
331 	if (ct != NULL) {
332 		tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
333 		zone = nf_ct_zone(ct);
334 	} else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
335 				      par->family, net, &tuple)) {
336 		goto hotdrop;
337 	}
338 
339 	if (par->family == NFPROTO_IPV6) {
340 		const struct ipv6hdr *iph = ipv6_hdr(skb);
341 		memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
342 		       &iph->daddr : &iph->saddr, sizeof(addr.ip6));
343 	} else {
344 		const struct iphdr *iph = ip_hdr(skb);
345 		addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
346 			  iph->daddr : iph->saddr;
347 	}
348 
349 	connections = count_them(net, info->data, tuple_ptr, &addr,
350 	                         &info->mask, par->family, zone);
351 	if (connections == 0)
352 		/* kmalloc failed, drop it entirely */
353 		goto hotdrop;
354 
355 	return (connections > info->limit) ^
356 	       !!(info->flags & XT_CONNLIMIT_INVERT);
357 
358  hotdrop:
359 	par->hotdrop = true;
360 	return false;
361 }
362 
363 static int connlimit_mt_check(const struct xt_mtchk_param *par)
364 {
365 	struct xt_connlimit_info *info = par->matchinfo;
366 	unsigned int i;
367 	int ret;
368 
369 	if (unlikely(!connlimit_rnd)) {
370 		u_int32_t rand;
371 
372 		do {
373 			get_random_bytes(&rand, sizeof(rand));
374 		} while (!rand);
375 		cmpxchg(&connlimit_rnd, 0, rand);
376 	}
377 	ret = nf_ct_l3proto_try_module_get(par->family);
378 	if (ret < 0) {
379 		pr_info("cannot load conntrack support for "
380 			"address family %u\n", par->family);
381 		return ret;
382 	}
383 
384 	/* init private data */
385 	info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
386 	if (info->data == NULL) {
387 		nf_ct_l3proto_module_put(par->family);
388 		return -ENOMEM;
389 	}
390 
391 	for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
392 		info->data->climit_root4[i] = RB_ROOT;
393 	for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
394 		info->data->climit_root6[i] = RB_ROOT;
395 
396 	return 0;
397 }
398 
399 static void destroy_tree(struct rb_root *r)
400 {
401 	struct xt_connlimit_conn *conn;
402 	struct xt_connlimit_rb *rbconn;
403 	struct hlist_node *n;
404 	struct rb_node *node;
405 
406 	while ((node = rb_first(r)) != NULL) {
407 		rbconn = container_of(node, struct xt_connlimit_rb, node);
408 
409 		rb_erase(node, r);
410 
411 		hlist_for_each_entry_safe(conn, n, &rbconn->hhead, node)
412 			kmem_cache_free(connlimit_conn_cachep, conn);
413 
414 		kmem_cache_free(connlimit_rb_cachep, rbconn);
415 	}
416 }
417 
418 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
419 {
420 	const struct xt_connlimit_info *info = par->matchinfo;
421 	unsigned int i;
422 
423 	nf_ct_l3proto_module_put(par->family);
424 
425 	for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
426 		destroy_tree(&info->data->climit_root4[i]);
427 	for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
428 		destroy_tree(&info->data->climit_root6[i]);
429 
430 	kfree(info->data);
431 }
432 
433 static struct xt_match connlimit_mt_reg __read_mostly = {
434 	.name       = "connlimit",
435 	.revision   = 1,
436 	.family     = NFPROTO_UNSPEC,
437 	.checkentry = connlimit_mt_check,
438 	.match      = connlimit_mt,
439 	.matchsize  = sizeof(struct xt_connlimit_info),
440 	.destroy    = connlimit_mt_destroy,
441 	.me         = THIS_MODULE,
442 };
443 
444 static int __init connlimit_mt_init(void)
445 {
446 	int ret, i;
447 
448 	BUILD_BUG_ON(CONNLIMIT_LOCK_SLOTS > CONNLIMIT_SLOTS);
449 	BUILD_BUG_ON((CONNLIMIT_SLOTS % CONNLIMIT_LOCK_SLOTS) != 0);
450 
451 	for (i = 0; i < CONNLIMIT_LOCK_SLOTS; ++i)
452 		spin_lock_init(&xt_connlimit_locks[i]);
453 
454 	connlimit_conn_cachep = kmem_cache_create("xt_connlimit_conn",
455 					   sizeof(struct xt_connlimit_conn),
456 					   0, 0, NULL);
457 	if (!connlimit_conn_cachep)
458 		return -ENOMEM;
459 
460 	connlimit_rb_cachep = kmem_cache_create("xt_connlimit_rb",
461 					   sizeof(struct xt_connlimit_rb),
462 					   0, 0, NULL);
463 	if (!connlimit_rb_cachep) {
464 		kmem_cache_destroy(connlimit_conn_cachep);
465 		return -ENOMEM;
466 	}
467 	ret = xt_register_match(&connlimit_mt_reg);
468 	if (ret != 0) {
469 		kmem_cache_destroy(connlimit_conn_cachep);
470 		kmem_cache_destroy(connlimit_rb_cachep);
471 	}
472 	return ret;
473 }
474 
475 static void __exit connlimit_mt_exit(void)
476 {
477 	xt_unregister_match(&connlimit_mt_reg);
478 	kmem_cache_destroy(connlimit_conn_cachep);
479 	kmem_cache_destroy(connlimit_rb_cachep);
480 }
481 
482 module_init(connlimit_mt_init);
483 module_exit(connlimit_mt_exit);
484 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
485 MODULE_DESCRIPTION("Xtables: Number of connections matching");
486 MODULE_LICENSE("GPL");
487 MODULE_ALIAS("ipt_connlimit");
488 MODULE_ALIAS("ip6t_connlimit");
489