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/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 list_head list;
  37         struct nf_conntrack_tuple tuple;
  38 };
  39
  40 struct xt_connlimit_data {
  41         struct list_head iphash[256];
  42         spinlock_t lock;
  43 };
  44
  45 static u_int32_t connlimit_rnd __read_mostly;
  46 static bool connlimit_rnd_inited __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                       unsigned int threshold)
 102 {
 103         const struct nf_conntrack_tuple_hash *found;
 104         struct xt_connlimit_conn *conn;
 105         struct xt_connlimit_conn *tmp;
 106         struct nf_conn *found_ct;
 107         struct list_head *hash;
 108         bool addit = true;
 109         int matches = 0;
 110
 111         if (family == NFPROTO_IPV6)
 112                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 113         else
 114                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 115
 116         rcu_read_lock();
 117
 118         /* check the saved connections */
 119         list_for_each_entry_safe(conn, tmp, hash, list) {
 120                 found    = nf_conntrack_find_get(net, NF_CT_DEFAULT_ZONE,
 121                                                  &conn->tuple);
 122                 found_ct = NULL;
 123
 124                 if (found != NULL)
 125                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 126
 127                 if (found_ct != NULL &&
 128                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 129                     !already_closed(found_ct))
 130                         /*
 131                          * Just to be sure we have it only once in the list.
 132                          * We should not see tuples twice unless someone hooks
 133                          * this into a table without "-p tcp --syn".
 134                          */
 135                         addit = false;
 136
 137                 if (found == NULL) {
 138                         /* this one is gone */
 139                         list_del(&conn->list);
 140                         kfree(conn);
 141                         continue;
 142                 }
 143
 144                 if (already_closed(found_ct)) {
 145                         /*
 146                          * we do not care about connections which are
 147                          * closed already -> ditch it
 148                          */
 149                         nf_ct_put(found_ct);
 150                         list_del(&conn->list);
 151                         kfree(conn);
 152                         continue;
 153                 }
 154
 155                 if (same_source_net(addr, mask, &conn->tuple.src.u3, family)) {
 156                         /* same source network -> be counted! */
 157                         ++matches;
 158                         if (matches > threshold) {
 159                                 nf_ct_put(found_ct);
 160                                 break;
 161                         }
 162                 }
 163                 nf_ct_put(found_ct);
 164         }
 165
 166         rcu_read_unlock();
 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
 182 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 183 {
 184         struct net *net = dev_net(par->in ? par->in : par->out);
 185         const struct xt_connlimit_info *info = par->matchinfo;
 186         union nf_inet_addr addr;
 187         struct nf_conntrack_tuple tuple;
 188         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 189         enum ip_conntrack_info ctinfo;
 190         const struct nf_conn *ct;
 191         int connections;
 192
 193         ct = nf_ct_get(skb, &ctinfo);
 194         if (ct != NULL) {
 195                 if (info->flags & XT_CONNLIMIT_DADDR)
 196                         tuple_ptr = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
 197                 else
 198                         tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 199         } else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 200                                     par->family, &tuple)) {
 201                 goto hotdrop;
 202         }
 203
 204         if (par->family == NFPROTO_IPV6) {
 205                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 206                 memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
 207                        &iph->daddr : &iph->saddr, sizeof(addr.ip6));
 208         } else {
 209                 const struct iphdr *iph = ip_hdr(skb);
 210                 addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
 211                           iph->daddr : iph->saddr;
 212         }
 213
 214         spin_lock_bh(&info->data->lock);
 215         connections = count_them(net, info->data, tuple_ptr, &addr,
 216                                  &info->mask, par->family,
 217                                  info->limit);
 218         spin_unlock_bh(&info->data->lock);
 219
 220         if (connections < 0)
 221                 /* kmalloc failed, drop it entirely */
 222                 goto hotdrop;
 223
 224         return (connections > info->limit) ^
 225                !!(info->flags & XT_CONNLIMIT_INVERT);
 226
 227  hotdrop:
 228         par->hotdrop = true;
 229         return false;
 230 }
 231
 232 static int connlimit_mt_check(const struct xt_mtchk_param *par)
 233 {
 234         struct xt_connlimit_info *info = par->matchinfo;
 235         unsigned int i;
 236         int ret;
 237
 238         if (unlikely(!connlimit_rnd_inited)) {
 239                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
 240                 connlimit_rnd_inited = true;
 241         }
 242         ret = nf_ct_l3proto_try_module_get(par->family);
 243         if (ret < 0) {
 244                 pr_info("cannot load conntrack support for "
 245                         "address family %u\n", par->family);
 246                 return ret;
 247         }
 248
 249         /* init private data */
 250         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 251         if (info->data == NULL) {
 252                 nf_ct_l3proto_module_put(par->family);
 253                 return -ENOMEM;
 254         }
 255
 256         spin_lock_init(&info->data->lock);
 257         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 258                 INIT_LIST_HEAD(&info->data->iphash[i]);
 259
 260         return 0;
 261 }
 262
 263 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
 264 {
 265         const struct xt_connlimit_info *info = par->matchinfo;
 266         struct xt_connlimit_conn *conn;
 267         struct xt_connlimit_conn *tmp;
 268         struct list_head *hash = info->data->iphash;
 269         unsigned int i;
 270
 271         nf_ct_l3proto_module_put(par->family);
 272
 273         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 274                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 275                         list_del(&conn->list);
 276                         kfree(conn);
 277                 }
 278         }
 279
 280         kfree(info->data);
 281 }
 282
 283 static struct xt_match connlimit_mt_reg[] __read_mostly = {
 284         {
 285                 .name       = "connlimit",
 286                 .revision   = 0,
 287                 .family     = NFPROTO_UNSPEC,
 288                 .checkentry = connlimit_mt_check,
 289                 .match      = connlimit_mt,
 290                 .matchsize  = sizeof(struct xt_connlimit_info),
 291                 .destroy    = connlimit_mt_destroy,
 292                 .me         = THIS_MODULE,
 293         },
 294         {
 295                 .name       = "connlimit",
 296                 .revision   = 1,
 297                 .family     = NFPROTO_UNSPEC,
 298                 .checkentry = connlimit_mt_check,
 299                 .match      = connlimit_mt,
 300                 .matchsize  = sizeof(struct xt_connlimit_info),
 301                 .destroy    = connlimit_mt_destroy,
 302                 .me         = THIS_MODULE,
 303         },
 304 };
 305
 306 static int __init connlimit_mt_init(void)
 307 {
 308         return xt_register_matches(connlimit_mt_reg,
 309                ARRAY_SIZE(connlimit_mt_reg));
 310 }
 311
 312 static void __exit connlimit_mt_exit(void)
 313 {
 314         xt_unregister_matches(connlimit_mt_reg, ARRAY_SIZE(connlimit_mt_reg));
 315 }
 316
 317 module_init(connlimit_mt_init);
 318 module_exit(connlimit_mt_exit);
 319 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 320 MODULE_DESCRIPTION("Xtables: Number of connections matching");
 321 MODULE_LICENSE("GPL");
 322 MODULE_ALIAS("ipt_connlimit");
 323 MODULE_ALIAS("ip6t_connlimit");