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  *   Copyright © Jan Engelhardt <jengelh@gmx.de>, 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 #include <linux/in.h>
  15 #include <linux/in6.h>
  16 #include <linux/ip.h>
  17 #include <linux/ipv6.h>
  18 #include <linux/jhash.h>
  19 #include <linux/list.h>
  20 #include <linux/module.h>
  21 #include <linux/random.h>
  22 #include <linux/skbuff.h>
  23 #include <linux/spinlock.h>
  24 #include <linux/netfilter/nf_conntrack_tcp.h>
  25 #include <linux/netfilter/x_tables.h>
  26 #include <linux/netfilter/xt_connlimit.h>
  27 #include <net/netfilter/nf_conntrack.h>
  28 #include <net/netfilter/nf_conntrack_core.h>
  29 #include <net/netfilter/nf_conntrack_tuple.h>
  30
  31 /* we will save the tuples of all connections we care about */
  32 struct xt_connlimit_conn {
  33         struct list_head list;
  34         struct nf_conntrack_tuple tuple;
  35 };
  36
  37 struct xt_connlimit_data {
  38         struct list_head iphash[256];
  39         spinlock_t lock;
  40 };
  41
  42 static u_int32_t connlimit_rnd;
  43 static bool connlimit_rnd_inited;
  44
  45 static inline unsigned int connlimit_iphash(__be32 addr)
  46 {
  47         if (unlikely(!connlimit_rnd_inited)) {
  48                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  49                 connlimit_rnd_inited = true;
  50         }
  51         return jhash_1word((__force __u32)addr, connlimit_rnd) & 0xFF;
  52 }
  53
  54 static inline unsigned int
  55 connlimit_iphash6(const union nf_conntrack_address *addr,
  56                   const union nf_conntrack_address *mask)
  57 {
  58         union nf_conntrack_address res;
  59         unsigned int i;
  60
  61         if (unlikely(!connlimit_rnd_inited)) {
  62                 get_random_bytes(&connlimit_rnd, sizeof(connlimit_rnd));
  63                 connlimit_rnd_inited = true;
  64         }
  65
  66         for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
  67                 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
  68
  69         return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6), connlimit_rnd) & 0xFF;
  70 }
  71
  72 static inline bool already_closed(const struct nf_conn *conn)
  73 {
  74         u_int16_t proto = conn->tuplehash[0].tuple.dst.protonum;
  75
  76         if (proto == IPPROTO_TCP)
  77                 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT;
  78         else
  79                 return 0;
  80 }
  81
  82 static inline unsigned int
  83 same_source_net(const union nf_conntrack_address *addr,
  84                 const union nf_conntrack_address *mask,
  85                 const union nf_conntrack_address *u3, unsigned int family)
  86 {
  87         if (family == AF_INET) {
  88                 return (addr->ip & mask->ip) == (u3->ip & mask->ip);
  89         } else {
  90                 union nf_conntrack_address lh, rh;
  91                 unsigned int i;
  92
  93                 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
  94                         lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
  95                         rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
  96                 }
  97
  98                 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6)) == 0;
  99         }
 100 }
 101
 102 static int count_them(struct xt_connlimit_data *data,
 103                       const struct nf_conntrack_tuple *tuple,
 104                       const union nf_conntrack_address *addr,
 105                       const union nf_conntrack_address *mask,
 106                       const struct xt_match *match)
 107 {
 108         struct nf_conntrack_tuple_hash *found;
 109         struct xt_connlimit_conn *conn;
 110         struct xt_connlimit_conn *tmp;
 111         struct nf_conn *found_ct;
 112         struct list_head *hash;
 113         bool addit = true;
 114         int matches = 0;
 115
 116
 117         if (match->family == AF_INET6)
 118                 hash = &data->iphash[connlimit_iphash6(addr, mask)];
 119         else
 120                 hash = &data->iphash[connlimit_iphash(addr->ip & mask->ip)];
 121
 122         read_lock_bh(&nf_conntrack_lock);
 123
 124         /* check the saved connections */
 125         list_for_each_entry_safe(conn, tmp, hash, list) {
 126                 found    = __nf_conntrack_find(&conn->tuple, NULL);
 127                 found_ct = NULL;
 128
 129                 if (found != NULL)
 130                         found_ct = nf_ct_tuplehash_to_ctrack(found);
 131
 132                 if (found_ct != NULL &&
 133                     nf_ct_tuple_equal(&conn->tuple, tuple) &&
 134                     !already_closed(found_ct))
 135                         /*
 136                          * Just to be sure we have it only once in the list.
 137                          * We should not see tuples twice unless someone hooks
 138                          * this into a table without "-p tcp --syn".
 139                          */
 140                         addit = false;
 141
 142                 if (found == NULL) {
 143                         /* this one is gone */
 144                         list_del(&conn->list);
 145                         kfree(conn);
 146                         continue;
 147                 }
 148
 149                 if (already_closed(found_ct)) {
 150                         /*
 151                          * we do not care about connections which are
 152                          * closed already -> ditch it
 153                          */
 154                         list_del(&conn->list);
 155                         kfree(conn);
 156                         continue;
 157                 }
 158
 159                 if (same_source_net(addr, mask, &conn->tuple.src.u3,
 160                     match->family))
 161                         /* same source network -> be counted! */
 162                         ++matches;
 163         }
 164
 165         read_unlock_bh(&nf_conntrack_lock);
 166
 167         if (addit) {
 168                 /* save the new connection in our list */
 169                 conn = kzalloc(sizeof(*conn), GFP_ATOMIC);
 170                 if (conn == NULL)
 171                         return -ENOMEM;
 172                 conn->tuple = *tuple;
 173                 list_add(&conn->list, hash);
 174                 ++matches;
 175         }
 176
 177         return matches;
 178 }
 179
 180 static bool connlimit_match(const struct sk_buff *skb,
 181                             const struct net_device *in,
 182                             const struct net_device *out,
 183                             const struct xt_match *match,
 184                             const void *matchinfo, int offset,
 185                             unsigned int protoff, bool *hotdrop)
 186 {
 187         const struct xt_connlimit_info *info = matchinfo;
 188         union nf_conntrack_address addr, mask;
 189         struct nf_conntrack_tuple tuple;
 190         const struct nf_conntrack_tuple *tuple_ptr = &tuple;
 191         enum ip_conntrack_info ctinfo;
 192         const struct nf_conn *ct;
 193         int connections;
 194
 195         ct = nf_ct_get(skb, &ctinfo);
 196         if (ct != NULL)
 197                 tuple_ptr = &ct->tuplehash[0].tuple;
 198         else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
 199                                     match->family, &tuple))
 200                 goto hotdrop;
 201
 202         if (match->family == AF_INET6) {
 203                 const struct ipv6hdr *iph = ipv6_hdr(skb);
 204                 memcpy(&addr.ip6, &iph->saddr, sizeof(iph->saddr));
 205                 memcpy(&mask.ip6, info->v6_mask, sizeof(info->v6_mask));
 206         } else {
 207                 const struct iphdr *iph = ip_hdr(skb);
 208                 addr.ip = iph->saddr;
 209                 mask.ip = info->v4_mask;
 210         }
 211
 212         spin_lock_bh(&info->data->lock);
 213         connections = count_them(info->data, tuple_ptr, &addr, &mask, match);
 214         spin_unlock_bh(&info->data->lock);
 215
 216         if (connections < 0) {
 217                 /* kmalloc failed, drop it entirely */
 218                 *hotdrop = true;
 219                 return false;
 220         }
 221
 222         return (connections > info->limit) ^ info->inverse;
 223
 224  hotdrop:
 225         *hotdrop = true;
 226         return false;
 227 }
 228
 229 static bool connlimit_check(const char *tablename, const void *ip,
 230                             const struct xt_match *match, void *matchinfo,
 231                             unsigned int hook_mask)
 232 {
 233         struct xt_connlimit_info *info = matchinfo;
 234         unsigned int i;
 235
 236         if (nf_ct_l3proto_try_module_get(match->family) < 0) {
 237                 printk(KERN_WARNING "cannot load conntrack support for "
 238                        "address family %u\n", match->family);
 239                 return false;
 240         }
 241
 242         /* init private data */
 243         info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
 244         if (info->data == NULL) {
 245                 nf_ct_l3proto_module_put(match->family);
 246                 return false;
 247         }
 248
 249         spin_lock_init(&info->data->lock);
 250         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i)
 251                 INIT_LIST_HEAD(&info->data->iphash[i]);
 252
 253         return true;
 254 }
 255
 256 static void connlimit_destroy(const struct xt_match *match, void *matchinfo)
 257 {
 258         struct xt_connlimit_info *info = matchinfo;
 259         struct xt_connlimit_conn *conn;
 260         struct xt_connlimit_conn *tmp;
 261         struct list_head *hash = info->data->iphash;
 262         unsigned int i;
 263
 264         nf_ct_l3proto_module_put(match->family);
 265
 266         for (i = 0; i < ARRAY_SIZE(info->data->iphash); ++i) {
 267                 list_for_each_entry_safe(conn, tmp, &hash[i], list) {
 268                         list_del(&conn->list);
 269                         kfree(conn);
 270                 }
 271         }
 272
 273         kfree(info->data);
 274 }
 275
 276 static struct xt_match connlimit_reg[] __read_mostly = {
 277         {
 278                 .name       = "connlimit",
 279                 .family     = AF_INET,
 280                 .checkentry = connlimit_check,
 281                 .match      = connlimit_match,
 282                 .matchsize  = sizeof(struct xt_connlimit_info),
 283                 .destroy    = connlimit_destroy,
 284                 .me         = THIS_MODULE,
 285         },
 286         {
 287                 .name       = "connlimit",
 288                 .family     = AF_INET6,
 289                 .checkentry = connlimit_check,
 290                 .match      = connlimit_match,
 291                 .matchsize  = sizeof(struct xt_connlimit_info),
 292                 .destroy    = connlimit_destroy,
 293                 .me         = THIS_MODULE,
 294         },
 295 };
 296
 297 static int __init xt_connlimit_init(void)
 298 {
 299         return xt_register_matches(connlimit_reg, ARRAY_SIZE(connlimit_reg));
 300 }
 301
 302 static void __exit xt_connlimit_exit(void)
 303 {
 304         xt_unregister_matches(connlimit_reg, ARRAY_SIZE(connlimit_reg));
 305 }
 306
 307 module_init(xt_connlimit_init);
 308 module_exit(xt_connlimit_exit);
 309 MODULE_AUTHOR("Jan Engelhardt <jengelh@gmx.de>");
 310 MODULE_DESCRIPTION("netfilter xt_connlimit match module");
 311 MODULE_LICENSE("GPL");
 312 MODULE_ALIAS("ipt_connlimit");
 313 MODULE_ALIAS("ip6t_connlimit");