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 *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 } 175 176 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 *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 } 276 277 static struct xt_match connlimit_mt_reg[] __read_mostly = { 278 { 279 .name = "connlimit", 280 .revision = 0, 281 .family = NFPROTO_UNSPEC, 282 .checkentry = connlimit_mt_check, 283 .match = connlimit_mt, 284 .matchsize = sizeof(struct xt_connlimit_info), 285 .destroy = connlimit_mt_destroy, 286 .me = THIS_MODULE, 287 }, 288 { 289 .name = "connlimit", 290 .revision = 1, 291 .family = NFPROTO_UNSPEC, 292 .checkentry = connlimit_mt_check, 293 .match = connlimit_mt, 294 .matchsize = sizeof(struct xt_connlimit_info), 295 .destroy = connlimit_mt_destroy, 296 .me = THIS_MODULE, 297 }, 298 }; 299 300 static int __init connlimit_mt_init(void) 301 { 302 return xt_register_matches(connlimit_mt_reg, 303 ARRAY_SIZE(connlimit_mt_reg)); 304 } 305 306 static void __exit connlimit_mt_exit(void) 307 { 308 xt_unregister_matches(connlimit_mt_reg, ARRAY_SIZE(connlimit_mt_reg)); 309 } 310 311 module_init(connlimit_mt_init); 312 module_exit(connlimit_mt_exit); 313 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); 314 MODULE_DESCRIPTION("Xtables: Number of connections matching"); 315 MODULE_LICENSE("GPL"); 316 MODULE_ALIAS("ipt_connlimit"); 317 MODULE_ALIAS("ip6t_connlimit"); 318