xt_connlimit.c revision 68c07cb6d8aa05daf38ab47d5bb674d81a2066fb 
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/module.h>
23#include <linux/random.h>
24#include <linux/skbuff.h>
25#include <linux/spinlock.h>
26#include <linux/netfilter/nf_conntrack_tcp.h>
27#include <linux/netfilter/x_tables.h>
28#include <linux/netfilter/xt_connlimit.h>
29#include <net/netfilter/nf_conntrack.h>
30#include <net/netfilter/nf_conntrack_core.h>
31#include <net/netfilter/nf_conntrack_tuple.h>
32#include <net/netfilter/nf_conntrack_zones.h>
33
34/* we will save the tuples of all connections we care about */
35struct xt_connlimit_conn {
36	struct hlist_node		node;
37	struct nf_conntrack_tuple	tuple;
38	union nf_inet_addr		addr;
39};
40
41struct xt_connlimit_data {
42	struct hlist_head	iphash[256];
43	spinlock_t		lock;
44};
45
46static u_int32_t connlimit_rnd __read_mostly;
47
48static inline unsigned int connlimit_iphash(__be32 addr)
49{
50	return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
51}
52
53static inline unsigned int
54connlimit_iphash6(const union nf_inet_addr *addr,
55                  const union nf_inet_addr *mask)
56{
57	union nf_inet_addr res;
58	unsigned int i;
59
60	for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
61		res.ip6[i] = addr->ip6[i] & mask->ip6[i];
62
63	return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
64}
65
66static inline bool already_closed(const struct nf_conn *conn)
67{
68	if (nf_ct_protonum(conn) == IPPROTO_TCP)
69		return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
70		       conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
71	else
72		return 0;
73}
74
75static inline unsigned int
76same_source_net(const union nf_inet_addr *addr,
77		const union nf_inet_addr *mask,
78		const union nf_inet_addr *u3, u_int8_t family)
79{
80	if (family == NFPROTO_IPV4) {
81		return (addr->ip & mask->ip) == (u3->ip & mask->ip);
82	} else {
83		union nf_inet_addr lh, rh;
84		unsigned int i;
85
86		for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
87			lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
88			rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
89		}
90
91		return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
92	}
93}
94
95static int count_them(struct net *net,
96		      struct xt_connlimit_data *data,
97		      const struct nf_conntrack_tuple *tuple,
98		      const union nf_inet_addr *addr,
99		      const union nf_inet_addr *mask,
100		      u_int8_t family)
101{
102	const struct nf_conntrack_tuple_hash *found;
103	struct xt_connlimit_conn *conn;
104	struct hlist_node *pos, *n;
105	struct nf_conn *found_ct;
106	struct hlist_head *hash;
107	bool addit = true;
108	int matches = 0;
109
110	if (family == NFPROTO_IPV6)
111		hash = &data->iphash[connlimit_iphash6(addr, mask)];
112	else
113		hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
114
115	rcu_read_lock();
116
117	/* check the saved connections */
118	hlist_for_each_entry_safe(conn, pos, n, hash, node) {
119		found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
120						 &conn->tuple);
121		found_ct = NULL;
122
123		if (found != NULL)
124			found_ct = nf_ct_tuplehash_to_ctrack(found);
125
126		if (found_ct != NULL &&
127		    nf_ct_tuple_equal(&conn->tuple, tuple) &&
128		    !already_closed(found_ct))
129			/*
130			 * Just to be sure we have it only once in the list.
131			 * We should not see tuples twice unless someone hooks
132			 * this into a table without "-p tcp --syn".
133			 */
134			addit = false;
135
136		if (found == NULL) {
137			/* this one is gone */
138			hlist_del(&conn->node);
139			kfree(conn);
140			continue;
141		}
142
143		if (already_closed(found_ct)) {
144			/*
145			 * we do not care about connections which are
146			 * closed already -> ditch it
147			 */
148			nf_ct_put(found_ct);
149			hlist_del(&conn->node);
150			kfree(conn);
151			continue;
152		}
153
154		if (same_source_net(addr, mask, &conn->addr, family))
155			/* same source network -> be counted! */
156			++matches;
157		nf_ct_put(found_ct);
158	}
159
160	rcu_read_unlock();
161
162	if (addit) {
163		/* save the new connection in our list */
164		conn = kmalloc(sizeof(*conn), GFP_ATOMIC);
165		if (conn == NULL)
166			return -ENOMEM;
167		conn->tuple = *tuple;
168		conn->addr = *addr;
169		hlist_add_head(&conn->node, hash);
170		++matches;
171	}
172
173	return matches;
174}
175
176static bool
177connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
178{
179	struct net *net = dev_net(par->in ? par->in : par->out);
180	const struct xt_connlimit_info *info = par->matchinfo;
181	union nf_inet_addr addr;
182	struct nf_conntrack_tuple tuple;
183	const struct nf_conntrack_tuple *tuple_ptr = &tuple;
184	enum ip_conntrack_info ctinfo;
185	const struct nf_conn *ct;
186	int connections;
187
188	ct = nf_ct_get(skb, &ctinfo);
189	if (ct != NULL)
190		tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
191	else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
192				    par->family, &tuple))
193		goto hotdrop;
194
195	if (par->family == NFPROTO_IPV6) {
196		const struct ipv6hdr *iph = ipv6_hdr(skb);
197		memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
198		       &iph->daddr : &iph->saddr, sizeof(addr.ip6));
199	} else {
200		const struct iphdr *iph = ip_hdr(skb);
201		addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
202			  iph->daddr : iph->saddr;
203	}
204
205	spin_lock_bh(&info->data->lock);
206	connections = count_them(net, info->data, tuple_ptr, &addr,
207	                         &info->mask, par->family);
208	spin_unlock_bh(&info->data->lock);
209
210	if (connections < 0)
211		/* kmalloc failed, drop it entirely */
212		goto hotdrop;
213
214	return (connections > info->limit) ^
215	       !!(info->flags & XT_CONNLIMIT_INVERT);
216
217 hotdrop:
218	par->hotdrop = true;
219	return false;
220}
221
222static int connlimit_mt_check(const struct xt_mtchk_param *par)
223{
224	struct xt_connlimit_info *info = par->matchinfo;
225	unsigned int i;
226	int ret;
227
228	if (unlikely(!connlimit_rnd)) {
229		u_int32_t rand;
230
231		do {
232			get_random_bytes(&rand, sizeof(rand));
233		} while (!rand);
234		cmpxchg(&connlimit_rnd, 0, rand);
235	}
236	ret = nf_ct_l3proto_try_module_get(par->family);
237	if (ret < 0) {
238		pr_info("cannot load conntrack support for "
239			"address family %u\n", par->family);
240		return ret;
241	}
242
243	/* init private data */
244	info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
245	if (info->data == NULL) {
246		nf_ct_l3proto_module_put(par->family);
247		return -ENOMEM;
248	}
249
250	spin_lock_init(&info->data->lock);
251	for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
252		INIT_HLIST_HEAD(&info->data->iphash[i]);
253
254	return 0;
255}
256
257static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
258{
259	const struct xt_connlimit_info *info = par->matchinfo;
260	struct xt_connlimit_conn *conn;
261	struct hlist_node *pos, *n;
262	struct hlist_head *hash = info->data->iphash;
263	unsigned int i;
264
265	nf_ct_l3proto_module_put(par->family);
266
267	for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
268		hlist_for_each_entry_safe(conn, pos, n, &hash[i], node) {
269			hlist_del(&conn->node);
270			kfree(conn);
271		}
272	}
273
274	kfree(info->data);
275}
276
277static struct xt_match connlimit_mt_reg __read_mostly = {
278	.name       = "connlimit",
279	.revision   = 1,
280	.family     = NFPROTO_UNSPEC,
281	.checkentry = connlimit_mt_check,
282	.match      = connlimit_mt,
283	.matchsize  = sizeof(struct xt_connlimit_info),
284	.destroy    = connlimit_mt_destroy,
285	.me         = THIS_MODULE,
286};
287
288static int __init connlimit_mt_init(void)
289{
290	return xt_register_match(&connlimit_mt_reg);
291}
292
293static void __exit connlimit_mt_exit(void)
294{
295	xt_unregister_match(&connlimit_mt_reg);
296}
297
298module_init(connlimit_mt_init);
299module_exit(connlimit_mt_exit);
300MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
301MODULE_DESCRIPTION("Xtables: Number of connections matching");
302MODULE_LICENSE("GPL");
303MODULE_ALIAS("ipt_connlimit");
304MODULE_ALIAS("ip6t_connlimit");
305