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 * Contact: <jengelh@computergmbh.de>
9 *
10 * based on ...
11 *
12 * Kernel module to match connection tracking information.
13 * GPL (C) 1999 Rusty Russell (rusty@rustcorp.com.au).
14 */
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/list.h>
21 #include <linux/module.h>
22 #include <linux/random.h>
23 #include <linux/skbuff.h>
24 #include <linux/spinlock.h>
25 #include <linux/netfilter/nf_conntrack_tcp.h>
26 #include <linux/netfilter/x_tables.h>
27 #include <linux/netfilter/xt_connlimit.h>
28 #include <net/netfilter/nf_conntrack.h>
29 #include <net/netfilter/nf_conntrack_core.h>
30 #include <net/netfilter/nf_conntrack_tuple.h>
31
32 /* we will save the tuples of all connections we care about */
33 struct xt_connlimit_conn {
34 struct list_head list;
35 struct nf_conntrack_tuple tuple;
36 };
37
38 struct xt_connlimit_data {
39 struct list_head iphash[256];
40 spinlock_t lock;
41 };
42
43 static u_int32_t connlimit_rnd;
44 static bool connlimit_rnd_inited;
45
connlimit_iphash(__be32 addr)46 static inline unsigned int connlimit_iphash(__be32 addr)
47 {
48 if (unlikely(!connlimit_rnd_inited)) {
49 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
50 connlimit_rnd_inited = true;
51 }
52 return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
53 }
54
55 static inline unsigned int
connlimit_iphash6(const union nf_inet_addr * addr,const union nf_inet_addr * mask)56 connlimit_iphash6(const union nf_inet_addr *addr,
57 const union nf_inet_addr *mask)
58 {
59 union nf_inet_addr res;
60 unsigned int i;
61
62 if (unlikely(!connlimit_rnd_inited)) {
63 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
64 connlimit_rnd_inited = true;
65 }
66
67 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
68 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
69
70 return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
71 }
72
already_closed(const struct nf_conn * conn)73 static inline bool already_closed(const struct nf_conn *conn)
74 {
75 if (nf_ct_protonum(conn) == IPPROTO_TCP)
76 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
77 conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
78 else
79 return 0;
80 }
81
82 static inline unsigned int
same_source_net(const union nf_inet_addr * addr,const union nf_inet_addr * mask,const union nf_inet_addr * u3,u_int8_t family)83 same_source_net(const union nf_inet_addr *addr,
84 const union nf_inet_addr *mask,
85 const union nf_inet_addr *u3, u_int8_t family)
86 {
87 if (family == NFPROTO_IPV4) {
88 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
89 } else {
90 union nf_inet_addr lh, rh;
91 unsigned int i;
92
93 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
94 lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
95 rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
96 }
97
98 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
99 }
100 }
101
count_them(struct xt_connlimit_data * data,const struct nf_conntrack_tuple * tuple,const union nf_inet_addr * addr,const union nf_inet_addr * mask,const struct xt_match * match)102 static int count_them(struct xt_connlimit_data *data,
103 const struct nf_conntrack_tuple *tuple,
104 const union nf_inet_addr *addr,
105 const union nf_inet_addr *mask,
106 const struct xt_match *match)
107 {
108 const struct nf_conntrack_tuple_hash *found;
109 struct xt_connlimit_conn *conn;
110 struct xt_connlimit_conn *tmp;
111 const struct nf_conn *found_ct;
112 struct list_head *hash;
113 bool addit = true;
114 int matches = 0;
115
116
117 if (match->family == NFPROTO_IPV6)
118 hash = &data->iphash[connlimit_iphash6(addr, mask)];
119 else
120 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
121
122 rcu_read_lock();
123
124 /* check the saved connections */
125 list_for_each_entry_safe(conn, tmp, hash, list) {
126 found = __nf_conntrack_find(&init_net, &conn->tuple);
127 found_ct = NULL;
128
129 if (found != NULL)
130 found_ct = nf_ct_tuplehash_to_ctrack(found);
131
132 if (found_ct != NULL &&
133 nf_ct_tuple_equal(&conn->tuple, tuple) &&
134 !already_closed(found_ct))
135 /*
136 * Just to be sure we have it only once in the list.
137 * We should not see tuples twice unless someone hooks
138 * this into a table without "-p tcp --syn".
139 */
140 addit = false;
141
142 if (found == NULL) {
143 /* this one is gone */
144 list_del(&conn->list);
145 kfree(conn);
146 continue;
147 }
148
149 if (already_closed(found_ct)) {
150 /*
151 * we do not care about connections which are
152 * closed already -> ditch it
153 */
154 list_del(&conn->list);
155 kfree(conn);
156 continue;
157 }
158
159 if (same_source_net(addr, mask, &conn->tuple.src.u3,
160 match->family))
161 /* same source network -> be counted! */
162 ++matches;
163 }
164
165 rcu_read_unlock();
166
167 if (addit) {
168 /* save the new connection in our list */
169 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
170 if (conn == NULL)
171 return -ENOMEM;
172 conn->tuple = *tuple;
173 list_add(&conn->list, hash);
174 ++matches;
175 }
176
177 return matches;
178 }
179
180 static bool
connlimit_mt(const struct sk_buff * skb,const struct xt_match_param * par)181 connlimit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
182 {
183 const struct xt_connlimit_info *info = par->matchinfo;
184 union nf_inet_addr addr;
185 struct nf_conntrack_tuple tuple;
186 const struct nf_conntrack_tuple *tuple_ptr = &tuple;
187 enum ip_conntrack_info ctinfo;
188 const struct nf_conn *ct;
189 int connections;
190
191 ct = nf_ct_get(skb, &ctinfo);
192 if (ct != NULL)
193 tuple_ptr = &ct->tuplehash[0].tuple;
194 else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
195 par->family, &tuple))
196 goto hotdrop;
197
198 if (par->family == NFPROTO_IPV6) {
199 const struct ipv6hdr *iph = ipv6_hdr(skb);
200 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
201 } else {
202 const struct iphdr *iph = ip_hdr(skb);
203 addr.ip = iph->saddr;
204 }
205
206 spin_lock_bh(&info->data->lock);
207 connections = count_them(info->data, tuple_ptr, &addr,
208 &info->mask, par->match);
209 spin_unlock_bh(&info->data->lock);
210
211 if (connections < 0) {
212 /* kmalloc failed, drop it entirely */
213 *par->hotdrop = true;
214 return false;
215 }
216
217 return (connections > info->limit) ^ info->inverse;
218
219 hotdrop:
220 *par->hotdrop = true;
221 return false;
222 }
223
connlimit_mt_check(const struct xt_mtchk_param * par)224 static bool connlimit_mt_check(const struct xt_mtchk_param *par)
225 {
226 struct xt_connlimit_info *info = par->matchinfo;
227 unsigned int i;
228
229 if (nf_ct_l3proto_try_module_get(par->family) < 0) {
230 printk(KERN_WARNING "cannot load conntrack support for "
231 "address family %u\n", par->family);
232 return false;
233 }
234
235 /* init private data */
236 info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
237 if (info->data == NULL) {
238 nf_ct_l3proto_module_put(par->family);
239 return false;
240 }
241
242 spin_lock_init(&info->data->lock);
243 for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
244 INIT_LIST_HEAD(&info->data->iphash[i]);
245
246 return true;
247 }
248
connlimit_mt_destroy(const struct xt_mtdtor_param * par)249 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
250 {
251 const struct xt_connlimit_info *info = par->matchinfo;
252 struct xt_connlimit_conn *conn;
253 struct xt_connlimit_conn *tmp;
254 struct list_head *hash = info->data->iphash;
255 unsigned int i;
256
257 nf_ct_l3proto_module_put(par->family);
258
259 for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
260 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
261 list_del(&conn->list);
262 kfree(conn);
263 }
264 }
265
266 kfree(info->data);
267 }
268
269 static struct xt_match connlimit_mt_reg __read_mostly = {
270 .name = "connlimit",
271 .revision = 0,
272 .family = NFPROTO_UNSPEC,
273 .checkentry = connlimit_mt_check,
274 .match = connlimit_mt,
275 .matchsize = sizeof(struct xt_connlimit_info),
276 .destroy = connlimit_mt_destroy,
277 .me = THIS_MODULE,
278 };
279
connlimit_mt_init(void)280 static int __init connlimit_mt_init(void)
281 {
282 return xt_register_match(&connlimit_mt_reg);
283 }
284
connlimit_mt_exit(void)285 static void __exit connlimit_mt_exit(void)
286 {
287 xt_unregister_match(&connlimit_mt_reg);
288 }
289
290 module_init(connlimit_mt_init);
291 module_exit(connlimit_mt_exit);
292 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
293 MODULE_DESCRIPTION("Xtables: Number of connections matching");
294 MODULE_LICENSE("GPL");
295 MODULE_ALIAS("ipt_connlimit");
296 MODULE_ALIAS("ip6t_connlimit");
297