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