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Linux/net/netfilter/xt_connlimit.c

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  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 */
 35 struct xt_connlimit_conn {
 36         struct hlist_node               node;
 37         struct nf_conntrack_tuple       tuple;
 38         union nf_inet_addr              addr;
 39 };
 40 
 41 struct xt_connlimit_data {
 42         struct hlist_head       iphash[256];
 43         spinlock_t              lock;
 44 };
 45 
 46 static u_int32_t connlimit_rnd __read_mostly;
 47 
 48 static inline unsigned int connlimit_iphash(__be32 addr)
 49 {
 50         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
 51 }
 52 
 53 static inline unsigned int
 54 connlimit_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 
 66 static 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 
 75 static inline unsigned int
 76 same_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 
 95 static 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 *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, 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 
176 static bool
177 connlimit_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 
222 static 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 
257 static 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 *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, n, &hash[i], node) {
269                         hlist_del(&conn->node);
270                         kfree(conn);
271                 }
272         }
273 
274         kfree(info->data);
275 }
276 
277 static 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 
288 static int __init connlimit_mt_init(void)
289 {
290         return xt_register_match(&connlimit_mt_reg);
291 }
292 
293 static void __exit connlimit_mt_exit(void)
294 {
295         xt_unregister_match(&connlimit_mt_reg);
296 }
297 
298 module_init(connlimit_mt_init);
299 module_exit(connlimit_mt_exit);
300 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
301 MODULE_DESCRIPTION("Xtables: Number of connections matching");
302 MODULE_LICENSE("GPL");
303 MODULE_ALIAS("ipt_connlimit");
304 MODULE_ALIAS("ip6t_connlimit");
305 

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