netfilter: xtables: obtain random bytes earlier, in checkentry
[linux-2.6.git] / net / netfilter / xt_connlimit.c
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 __read_mostly;
44 static bool connlimit_rnd_inited __read_mostly;
45
46 static inline unsigned int connlimit_iphash(__be32 addr)
47 {
48         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
49 }
50
51 static inline unsigned int
52 connlimit_iphash6(const union nf_inet_addr *addr,
53                   const union nf_inet_addr *mask)
54 {
55         union nf_inet_addr res;
56         unsigned int i;
57
58         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
59                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
60
61         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
62 }
63
64 static inline bool already_closed(const struct nf_conn *conn)
65 {
66         if (nf_ct_protonum(conn) == IPPROTO_TCP)
67                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
68                        conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
69         else
70                 return 0;
71 }
72
73 static inline unsigned int
74 same_source_net(const union nf_inet_addr *addr,
75                 const union nf_inet_addr *mask,
76                 const union nf_inet_addr *u3, u_int8_t family)
77 {
78         if (family == NFPROTO_IPV4) {
79                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
80         } else {
81                 union nf_inet_addr lh, rh;
82                 unsigned int i;
83
84                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
85                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
86                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
87                 }
88
89                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
90         }
91 }
92
93 static int count_them(struct xt_connlimit_data *data,
94                       const struct nf_conntrack_tuple *tuple,
95                       const union nf_inet_addr *addr,
96                       const union nf_inet_addr *mask,
97                       u_int8_t family)
98 {
99         const struct nf_conntrack_tuple_hash *found;
100         struct xt_connlimit_conn *conn;
101         struct xt_connlimit_conn *tmp;
102         struct nf_conn *found_ct;
103         struct list_head *hash;
104         bool addit = true;
105         int matches = 0;
106
107         if (family == NFPROTO_IPV6)
108                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
109         else
110                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
111
112         rcu_read_lock();
113
114         /* check the saved connections */
115         list_for_each_entry_safe(conn, tmp, hash, list) {
116                 found    = nf_conntrack_find_get(&init_net, &conn->tuple);
117                 found_ct = NULL;
118
119                 if (found != NULL)
120                         found_ct = nf_ct_tuplehash_to_ctrack(found);
121
122                 if (found_ct != NULL &&
123                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
124                     !already_closed(found_ct))
125                         /*
126                          * Just to be sure we have it only once in the list.
127                          * We should not see tuples twice unless someone hooks
128                          * this into a table without "-p tcp --syn".
129                          */
130                         addit = false;
131
132                 if (found == NULL) {
133                         /* this one is gone */
134                         list_del(&conn->list);
135                         kfree(conn);
136                         continue;
137                 }
138
139                 if (already_closed(found_ct)) {
140                         /*
141                          * we do not care about connections which are
142                          * closed already -> ditch it
143                          */
144                         nf_ct_put(found_ct);
145                         list_del(&conn->list);
146                         kfree(conn);
147                         continue;
148                 }
149
150                 if (same_source_net(addr, mask, &conn->tuple.src.u3, family))
151                         /* same source network -> be counted! */
152                         ++matches;
153                 nf_ct_put(found_ct);
154         }
155
156         rcu_read_unlock();
157
158         if (addit) {
159                 /* save the new connection in our list */
160                 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
161                 if (conn == NULL)
162                         return -ENOMEM;
163                 conn->tuple = *tuple;
164                 list_add(&conn->list, hash);
165                 ++matches;
166         }
167
168         return matches;
169 }
170
171 static bool
172 connlimit_mt(const struct sk_buff *skb, const struct xt_match_param *par)
173 {
174         const struct xt_connlimit_info *info = par->matchinfo;
175         union nf_inet_addr addr;
176         struct nf_conntrack_tuple tuple;
177         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
178         enum ip_conntrack_info ctinfo;
179         const struct nf_conn *ct;
180         int connections;
181
182         ct = nf_ct_get(skb, &ctinfo);
183         if (ct != NULL)
184                 tuple_ptr = &ct->tuplehash[0].tuple;
185         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
186                                     par->family, &tuple))
187                 goto hotdrop;
188
189         if (par->family == NFPROTO_IPV6) {
190                 const struct ipv6hdr *iph = ipv6_hdr(skb);
191                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
192         } else {
193                 const struct iphdr *iph = ip_hdr(skb);
194                 addr.ip = iph->saddr;
195         }
196
197         spin_lock_bh(&info->data->lock);
198         connections = count_them(info->data, tuple_ptr, &addr,
199                                  &info->mask, par->family);
200         spin_unlock_bh(&info->data->lock);
201
202         if (connections < 0) {
203                 /* kmalloc failed, drop it entirely */
204                 *par->hotdrop = true;
205                 return false;
206         }
207
208         return (connections > info->limit) ^ info->inverse;
209
210  hotdrop:
211         *par->hotdrop = true;
212         return false;
213 }
214
215 static bool connlimit_mt_check(const struct xt_mtchk_param *par)
216 {
217         struct xt_connlimit_info *info = par->matchinfo;
218         unsigned int i;
219
220         if (unlikely(!connlimit_rnd_inited)) {
221                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
222                 connlimit_rnd_inited = true;
223         }
224         if (nf_ct_l3proto_try_module_get(par->family) < 0) {
225                 printk(KERN_WARNING "cannot load conntrack support for "
226                        "address family %u\n", par->family);
227                 return false;
228         }
229
230         /* init private data */
231         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
232         if (info->data == NULL) {
233                 nf_ct_l3proto_module_put(par->family);
234                 return false;
235         }
236
237         spin_lock_init(&info->data->lock);
238         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
239                 INIT_LIST_HEAD(&info->data->iphash[i]);
240
241         return true;
242 }
243
244 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
245 {
246         const struct xt_connlimit_info *info = par->matchinfo;
247         struct xt_connlimit_conn *conn;
248         struct xt_connlimit_conn *tmp;
249         struct list_head *hash = info->data->iphash;
250         unsigned int i;
251
252         nf_ct_l3proto_module_put(par->family);
253
254         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
255                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
256                         list_del(&conn->list);
257                         kfree(conn);
258                 }
259         }
260
261         kfree(info->data);
262 }
263
264 static struct xt_match connlimit_mt_reg __read_mostly = {
265         .name       = "connlimit",
266         .revision   = 0,
267         .family     = NFPROTO_UNSPEC,
268         .checkentry = connlimit_mt_check,
269         .match      = connlimit_mt,
270         .matchsize  = sizeof(struct xt_connlimit_info),
271         .destroy    = connlimit_mt_destroy,
272         .me         = THIS_MODULE,
273 };
274
275 static int __init connlimit_mt_init(void)
276 {
277         return xt_register_match(&connlimit_mt_reg);
278 }
279
280 static void __exit connlimit_mt_exit(void)
281 {
282         xt_unregister_match(&connlimit_mt_reg);
283 }
284
285 module_init(connlimit_mt_init);
286 module_exit(connlimit_mt_exit);
287 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
288 MODULE_DESCRIPTION("Xtables: Number of connections matching");
289 MODULE_LICENSE("GPL");
290 MODULE_ALIAS("ipt_connlimit");
291 MODULE_ALIAS("ip6t_connlimit");