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 */ 35struct xt_connlimit_conn { 36 struct list_head list; 37 struct nf_conntrack_tuple tuple; 38}; 39 40struct xt_connlimit_data { 41 struct list_head iphash[256]; 42 spinlock_t lock; 43}; 44 45static u_int32_t connlimit_rnd __read_mostly; 46static bool connlimit_rnd_inited __read_mostly; 47 48static inline unsigned int connlimit_iphash(__be32 addr) 49{ 50 return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF; 51} 52 53static inline unsigned int 54connlimit_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 66static 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 75static inline unsigned int 76same_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 95static 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 xt_connlimit_conn *tmp; 105 struct nf_conn *found_ct; 106 struct list_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 list_for_each_entry_safe(conn, tmp, hash, list) { 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 list_del(&conn->list); 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 list_del(&conn->list); 150 kfree(conn); 151 continue; 152 } 153 154 if (same_source_net(addr, mask, &conn->tuple.src.u3, 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 = kzalloc(sizeof(*conn), GFP_ATOMIC); 165 if (conn == NULL) 166 return -ENOMEM; 167 conn->tuple = *tuple; 168 list_add(&conn->list, hash); 169 ++matches; 170 } 171 172 return matches; 173} 174 175static bool 176connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par) 177{ 178 struct net *net = dev_net(par->in ? par->in : par->out); 179 const struct xt_connlimit_info *info = par->matchinfo; 180 union nf_inet_addr addr; 181 struct nf_conntrack_tuple tuple; 182 const struct nf_conntrack_tuple *tuple_ptr = &tuple; 183 enum ip_conntrack_info ctinfo; 184 const struct nf_conn *ct; 185 int connections; 186 187 ct = nf_ct_get(skb, &ctinfo); 188 if (ct != NULL) 189 tuple_ptr = &ct->tuplehash[0].tuple; 190 else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb), 191 par->family, &tuple)) 192 goto hotdrop; 193 194 if (par->family == NFPROTO_IPV6) { 195 const struct ipv6hdr *iph = ipv6_hdr(skb); 196 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr)); 197 } else { 198 const struct iphdr *iph = ip_hdr(skb); 199 addr.ip = iph->saddr; 200 } 201 202 spin_lock_bh(&info->data->lock); 203 connections = count_them(net, info->data, tuple_ptr, &addr, 204 &info->mask, par->family); 205 spin_unlock_bh(&info->data->lock); 206 207 if (connections < 0) { 208 /* kmalloc failed, drop it entirely */ 209 par->hotdrop = true; 210 return false; 211 } 212 213 return (connections > info->limit) ^ info->inverse; 214 215 hotdrop: 216 par->hotdrop = true; 217 return false; 218} 219 220static int connlimit_mt_check(const struct xt_mtchk_param *par) 221{ 222 struct xt_connlimit_info *info = par->matchinfo; 223 unsigned int i; 224 int ret; 225 226 if (unlikely(!connlimit_rnd_inited)) { 227 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd)); 228 connlimit_rnd_inited = true; 229 } 230 ret = nf_ct_l3proto_try_module_get(par->family); 231 if (ret < 0) { 232 pr_info("cannot load conntrack support for " 233 "address family %u\n", par->family); 234 return ret; 235 } 236 237 /* init private data */ 238 info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL); 239 if (info->data == NULL) { 240 nf_ct_l3proto_module_put(par->family); 241 return -ENOMEM; 242 } 243 244 spin_lock_init(&info->data->lock); 245 for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) 246 INIT_LIST_HEAD(&info->data->iphash[i]); 247 248 return 0; 249} 250 251static void connlimit_mt_destroy(const struct xt_mtdtor_param *par) 252{ 253 const struct xt_connlimit_info *info = par->matchinfo; 254 struct xt_connlimit_conn *conn; 255 struct xt_connlimit_conn *tmp; 256 struct list_head *hash = info->data->iphash; 257 unsigned int i; 258 259 nf_ct_l3proto_module_put(par->family); 260 261 for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) { 262 list_for_each_entry_safe(conn, tmp, &hash[i], list) { 263 list_del(&conn->list); 264 kfree(conn); 265 } 266 } 267 268 kfree(info->data); 269} 270 271static struct xt_match connlimit_mt_reg __read_mostly = { 272 .name = "connlimit", 273 .revision = 0, 274 .family = NFPROTO_UNSPEC, 275 .checkentry = connlimit_mt_check, 276 .match = connlimit_mt, 277 .matchsize = sizeof(struct xt_connlimit_info), 278 .destroy = connlimit_mt_destroy, 279 .me = THIS_MODULE, 280}; 281 282static int __init connlimit_mt_init(void) 283{ 284 return xt_register_match(&connlimit_mt_reg); 285} 286 287static void __exit connlimit_mt_exit(void) 288{ 289 xt_unregister_match(&connlimit_mt_reg); 290} 291 292module_init(connlimit_mt_init); 293module_exit(connlimit_mt_exit); 294MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>"); 295MODULE_DESCRIPTION("Xtables: Number of connections matching"); 296MODULE_LICENSE("GPL"); 297MODULE_ALIAS("ipt_connlimit"); 298MODULE_ALIAS("ip6t_connlimit"); 299