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;
  44 static bool connlimit_rnd_inited;
  45
  46 static inline unsigned int connlimit_iphash(__be32 addr)
  47 {
  48         if (unlikely(!connlimit_rnd_inited)) {
  49                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  50                 connlimit_rnd_inited = true;
  51         }
  52         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  53 }
  54
  55 static inline unsigned int
  56 connlimit_iphash6(const union nf_conntrack_address *addr,
  57                   const union nf_conntrack_address *mask)
  58 {
  59         union nf_conntrack_address res;
  60         unsigned int i;
  61
  62         if (unlikely(!connlimit_rnd_inited)) {
  63                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  64                 connlimit_rnd_inited = true;
  65         }
  66
  67         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  68                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  69
  70         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
  71 }
  72
  73 static inline bool already_closed(const struct nf_conn *conn)
  74 {
  75         u_int16_t proto = conn->tuplehash[0].tuple.dst.protonum;
  76
  77         if (proto == IPPROTO_TCP)
  78                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT;
  79         else
  80                 return 0;
  81 }
  82
  83 static inline unsigned int
  84 same_source_net(const union nf_conntrack_address *addr,
  85                 const union nf_conntrack_address *mask,
  86                 const union nf_conntrack_address *u3, unsigned int family)
  87 {
  88         if (family == AF_INET) {
  89                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  90         } else {
  91                 union nf_conntrack_address lh, rh;
  92                 unsigned int i;
  93
  94                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  95                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  96                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  97                 }
  98
  99                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
 100         }
 101 }
 102
 103 static int count_them(struct xt_connlimit_data *data,
 104                       const struct nf_conntrack_tuple *tuple,
 105                       const union nf_conntrack_address *addr,
 106                       const union nf_conntrack_address *mask,
 107                       const struct xt_match *match)
 108 {
 109         struct nf_conntrack_tuple_hash *found;
 110         struct xt_connlimit_conn *conn;
 111         struct xt_connlimit_conn *tmp;
 112         struct nf_conn *found_ct;
 113         struct list_head *hash;
 114         bool addit = true;
 115         int matches = 0;
 116
 117
 118         if (match->family == AF_INET6)
 119                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 120         else
 121                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 122
 123         read_lock_bh(&nf_conntrack_lock);
 124
 125         /* check the saved connections */
 126         list_for_each_entry_safe(conn, tmp, hash, list) {
 127                 found    = __nf_conntrack_find(&conn->tuple, NULL);
 128                 found_ct = NULL;
 129
 130                 if (found != NULL)
 131                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 132
 133                 if (found_ct != NULL &&
 134                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 135                     !already_closed(found_ct))
 136                         /*
 137                          * Just to be sure we have it only once in the list.
 138                          * We should not see tuples twice unless someone hooks
 139                          * this into a table without "-p tcp --syn".
 140                          */
 141                         addit = false;
 142
 143                 if (found == NULL) {
 144                         /* this one is gone */
 145                         list_del(&conn->list);
 146                         kfree(conn);
 147                         continue;
 148                 }
 149
 150                 if (already_closed(found_ct)) {
 151                         /*
 152                          * we do not care about connections which are
 153                          * closed already -> ditch it
 154                          */
 155                         list_del(&conn->list);
 156                         kfree(conn);
 157                         continue;
 158                 }
 159
 160                 if (same_source_net(addr, mask, &conn->tuple.src.u3,
 161                     match->family))
 162                         /* same source network -> be counted! */
 163                         ++matches;
 164         }
 165
 166         read_unlock_bh(&nf_conntrack_lock);
 167
 168         if (addit) {
 169                 /* save the new connection in our list */
 170                 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
 171                 if (conn == NULL)
 172                         return -ENOMEM;
 173                 conn->tuple = *tuple;
 174                 list_add(&conn->list, hash);
 175                 ++matches;
 176         }
 177
 178         return matches;
 179 }
 180
 181 static bool connlimit_match(const struct sk_buff *skb,
 182                             const struct net_device *in,
 183                             const struct net_device *out,
 184                             const struct xt_match *match,
 185                             const void *matchinfo, int offset,
 186                             unsigned int protoff, bool *hotdrop)
 187 {
 188         const struct xt_connlimit_info *info = matchinfo;
 189         union nf_conntrack_address addr, mask;
 190         struct nf_conntrack_tuple tuple;
 191         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 192         enum ip_conntrack_info ctinfo;
 193         const struct nf_conn *ct;
 194         int connections;
 195
 196         ct = nf_ct_get(skb, &ctinfo);
 197         if (ct != NULL)
 198                 tuple_ptr = &ct->tuplehash[0].tuple;
 199         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 200                                     match->family, &tuple))
 201                 goto hotdrop;
 202
 203         if (match->family == AF_INET6) {
 204                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 205                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
 206                 memcpy(&mask.ip6, info->v6_mask, sizeof(info->v6_mask));
 207         } else {
 208                 const struct iphdr *iph = ip_hdr(skb);
 209                 addr.ip = iph->saddr;
 210                 mask.ip = info->v4_mask;
 211         }
 212
 213         spin_lock_bh(&info->data->lock);
 214         connections = count_them(info->data, tuple_ptr, &addr, &mask, match);
 215         spin_unlock_bh(&info->data->lock);
 216
 217         if (connections < 0) {
 218                 /* kmalloc failed, drop it entirely */
 219                 *hotdrop = true;
 220                 return false;
 221         }
 222
 223         return (connections > info->limit) ^ info->inverse;
 224
 225  hotdrop:
 226         *hotdrop = true;
 227         return false;
 228 }
 229
 230 static bool connlimit_check(const char *tablename, const void *ip,
 231                             const struct xt_match *match, void *matchinfo,
 232                             unsigned int hook_mask)
 233 {
 234         struct xt_connlimit_info *info = matchinfo;
 235         unsigned int i;
 236
 237         if (nf_ct_l3proto_try_module_get(match->family) < 0) {
 238                 printk(KERN_WARNING "cannot load conntrack support for "
 239                        "address family %u\n", match->family);
 240                 return false;
 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(match->family);
 247                 return false;
 248         }
 249
 250         spin_lock_init(&info->data->lock);
 251         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 252                 INIT_LIST_HEAD(&info->data->iphash[i]);
 253
 254         return true;
 255 }
 256
 257 static void connlimit_destroy(const struct xt_match *match, void *matchinfo)
 258 {
 259         struct xt_connlimit_info *info = matchinfo;
 260         struct xt_connlimit_conn *conn;
 261         struct xt_connlimit_conn *tmp;
 262         struct list_head *hash = info->data->iphash;
 263         unsigned int i;
 264
 265         nf_ct_l3proto_module_put(match->family);
 266
 267         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 268                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 269                         list_del(&conn->list);
 270                         kfree(conn);
 271                 }
 272         }
 273
 274         kfree(info->data);
 275 }
 276
 277 static struct xt_match connlimit_reg[] __read_mostly = {
 278         {
 279                 .name       = "connlimit",
 280                 .family     = AF_INET,
 281                 .checkentry = connlimit_check,
 282                 .match      = connlimit_match,
 283                 .matchsize  = sizeof(struct xt_connlimit_info),
 284                 .destroy    = connlimit_destroy,
 285                 .me         = THIS_MODULE,
 286         },
 287         {
 288                 .name       = "connlimit",
 289                 .family     = AF_INET6,
 290                 .checkentry = connlimit_check,
 291                 .match      = connlimit_match,
 292                 .matchsize  = sizeof(struct xt_connlimit_info),
 293                 .destroy    = connlimit_destroy,
 294                 .me         = THIS_MODULE,
 295         },
 296 };
 297
 298 static int __init xt_connlimit_init(void)
 299 {
 300         return xt_register_matches(connlimit_reg, ARRAY_SIZE(connlimit_reg));
 301 }
 302
 303 static void __exit xt_connlimit_exit(void)
 304 {
 305         xt_unregister_matches(connlimit_reg, ARRAY_SIZE(connlimit_reg));
 306 }
 307
 308 module_init(xt_connlimit_init);
 309 module_exit(xt_connlimit_exit);
 310 MODULE_AUTHOR("Jan Engelhardt <jengelh@computergmbh.de>");
 311 MODULE_DESCRIPTION("netfilter xt_connlimit match module");
 312 MODULE_LICENSE("GPL");
 313 MODULE_ALIAS("ipt_connlimit");
 314 MODULE_ALIAS("ip6t_connlimit");