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/rbtree.h>
23 #include <linux/module.h>
24 #include <linux/random.h>
25 #include <linux/skbuff.h>
26 #include <linux/spinlock.h>
27 #include <linux/netfilter/nf_conntrack_tcp.h>
28 #include <linux/netfilter/x_tables.h>
29 #include <linux/netfilter/xt_connlimit.h>
30 #include <net/netfilter/nf_conntrack.h>
31 #include <net/netfilter/nf_conntrack_core.h>
32 #include <net/netfilter/nf_conntrack_tuple.h>
33 #include <net/netfilter/nf_conntrack_zones.h>
34
35 #define CONNLIMIT_SLOTS 256U
36
37 #ifdef CONFIG_LOCKDEP
38 #define CONNLIMIT_LOCK_SLOTS 8U
39 #else
40 #define CONNLIMIT_LOCK_SLOTS 256U
41 #endif
42
43 #define CONNLIMIT_GC_MAX_NODES 8
44
45 /* we will save the tuples of all connections we care about */
46 struct xt_connlimit_conn {
47 struct hlist_node node;
48 struct nf_conntrack_tuple tuple;
49 union nf_inet_addr addr;
50 };
51
52 struct xt_connlimit_rb {
53 struct rb_node node;
54 struct hlist_head hhead; /* connections/hosts in same subnet */
55 union nf_inet_addr addr; /* search key */
56 };
57
58 static spinlock_t xt_connlimit_locks[CONNLIMIT_LOCK_SLOTS] __cacheline_aligned_in_smp;
59
60 struct xt_connlimit_data {
61 struct rb_root climit_root4[CONNLIMIT_SLOTS];
62 struct rb_root climit_root6[CONNLIMIT_SLOTS];
63 };
64
65 static u_int32_t connlimit_rnd __read_mostly;
66 static struct kmem_cache *connlimit_rb_cachep __read_mostly;
67 static struct kmem_cache *connlimit_conn_cachep __read_mostly;
68
connlimit_iphash(__be32 addr)69 static inline unsigned int connlimit_iphash(__be32 addr)
70 {
71 return jhash_1word((__force __u32)addr,
72 connlimit_rnd) % CONNLIMIT_SLOTS;
73 }
74
75 static inline unsigned int
connlimit_iphash6(const union nf_inet_addr * addr,const union nf_inet_addr * mask)76 connlimit_iphash6(const union nf_inet_addr *addr,
77 const union nf_inet_addr *mask)
78 {
79 union nf_inet_addr res;
80 unsigned int i;
81
82 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i)
83 res.ip6[i] = addr->ip6[i] & mask->ip6[i];
84
85 return jhash2((u32 *)res.ip6, ARRAY_SIZE(res.ip6),
86 connlimit_rnd) % CONNLIMIT_SLOTS;
87 }
88
already_closed(const struct nf_conn * conn)89 static inline bool already_closed(const struct nf_conn *conn)
90 {
91 if (nf_ct_protonum(conn) == IPPROTO_TCP)
92 return conn->proto.tcp.state == TCP_CONNTRACK_TIME_WAIT ||
93 conn->proto.tcp.state == TCP_CONNTRACK_CLOSE;
94 else
95 return 0;
96 }
97
98 static int
same_source_net(const union nf_inet_addr * addr,const union nf_inet_addr * mask,const union nf_inet_addr * u3,u_int8_t family)99 same_source_net(const union nf_inet_addr *addr,
100 const union nf_inet_addr *mask,
101 const union nf_inet_addr *u3, u_int8_t family)
102 {
103 if (family == NFPROTO_IPV4) {
104 return ntohl(addr->ip & mask->ip) -
105 ntohl(u3->ip & mask->ip);
106 } else {
107 union nf_inet_addr lh, rh;
108 unsigned int i;
109
110 for (i = 0; i < ARRAY_SIZE(addr->ip6); ++i) {
111 lh.ip6[i] = addr->ip6[i] & mask->ip6[i];
112 rh.ip6[i] = u3->ip6[i] & mask->ip6[i];
113 }
114
115 return memcmp(&lh.ip6, &rh.ip6, sizeof(lh.ip6));
116 }
117 }
118
add_hlist(struct hlist_head * head,const struct nf_conntrack_tuple * tuple,const union nf_inet_addr * addr)119 static bool add_hlist(struct hlist_head *head,
120 const struct nf_conntrack_tuple *tuple,
121 const union nf_inet_addr *addr)
122 {
123 struct xt_connlimit_conn *conn;
124
125 conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
126 if (conn == NULL)
127 return false;
128 conn->tuple = *tuple;
129 conn->addr = *addr;
130 hlist_add_head(&conn->node, head);
131 return true;
132 }
133
check_hlist(struct net * net,struct hlist_head * head,const struct nf_conntrack_tuple * tuple,u16 zone,bool * addit)134 static unsigned int check_hlist(struct net *net,
135 struct hlist_head *head,
136 const struct nf_conntrack_tuple *tuple,
137 u16 zone,
138 bool *addit)
139 {
140 const struct nf_conntrack_tuple_hash *found;
141 struct xt_connlimit_conn *conn;
142 struct hlist_node *n;
143 struct nf_conn *found_ct;
144 unsigned int length = 0;
145
146 *addit = true;
147 rcu_read_lock();
148
149 /* check the saved connections */
150 hlist_for_each_entry_safe(conn, n, head, node) {
151 found = nf_conntrack_find_get(net, zone, &conn->tuple);
152 if (found == NULL) {
153 hlist_del(&conn->node);
154 kmem_cache_free(connlimit_conn_cachep, conn);
155 continue;
156 }
157
158 found_ct = nf_ct_tuplehash_to_ctrack(found);
159
160 if (nf_ct_tuple_equal(&conn->tuple, tuple)) {
161 /*
162 * Just to be sure we have it only once in the list.
163 * We should not see tuples twice unless someone hooks
164 * this into a table without "-p tcp --syn".
165 */
166 *addit = false;
167 } else if (already_closed(found_ct)) {
168 /*
169 * we do not care about connections which are
170 * closed already -> ditch it
171 */
172 nf_ct_put(found_ct);
173 hlist_del(&conn->node);
174 kmem_cache_free(connlimit_conn_cachep, conn);
175 continue;
176 }
177
178 nf_ct_put(found_ct);
179 length++;
180 }
181
182 rcu_read_unlock();
183
184 return length;
185 }
186
tree_nodes_free(struct rb_root * root,struct xt_connlimit_rb * gc_nodes[],unsigned int gc_count)187 static void tree_nodes_free(struct rb_root *root,
188 struct xt_connlimit_rb *gc_nodes[],
189 unsigned int gc_count)
190 {
191 struct xt_connlimit_rb *rbconn;
192
193 while (gc_count) {
194 rbconn = gc_nodes[--gc_count];
195 rb_erase(&rbconn->node, root);
196 kmem_cache_free(connlimit_rb_cachep, rbconn);
197 }
198 }
199
200 static unsigned int
count_tree(struct net * net,struct rb_root * root,const struct nf_conntrack_tuple * tuple,const union nf_inet_addr * addr,const union nf_inet_addr * mask,u8 family,u16 zone)201 count_tree(struct net *net, struct rb_root *root,
202 const struct nf_conntrack_tuple *tuple,
203 const union nf_inet_addr *addr, const union nf_inet_addr *mask,
204 u8 family, u16 zone)
205 {
206 struct xt_connlimit_rb *gc_nodes[CONNLIMIT_GC_MAX_NODES];
207 struct rb_node **rbnode, *parent;
208 struct xt_connlimit_rb *rbconn;
209 struct xt_connlimit_conn *conn;
210 unsigned int gc_count;
211 bool no_gc = false;
212
213 restart:
214 gc_count = 0;
215 parent = NULL;
216 rbnode = &(root->rb_node);
217 while (*rbnode) {
218 int diff;
219 bool addit;
220
221 rbconn = container_of(*rbnode, struct xt_connlimit_rb, node);
222
223 parent = *rbnode;
224 diff = same_source_net(addr, mask, &rbconn->addr, family);
225 if (diff < 0) {
226 rbnode = &((*rbnode)->rb_left);
227 } else if (diff > 0) {
228 rbnode = &((*rbnode)->rb_right);
229 } else {
230 /* same source network -> be counted! */
231 unsigned int count;
232 count = check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
233
234 tree_nodes_free(root, gc_nodes, gc_count);
235 if (!addit)
236 return count;
237
238 if (!add_hlist(&rbconn->hhead, tuple, addr))
239 return 0; /* hotdrop */
240
241 return count + 1;
242 }
243
244 if (no_gc || gc_count >= ARRAY_SIZE(gc_nodes))
245 continue;
246
247 /* only used for GC on hhead, retval and 'addit' ignored */
248 check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
249 if (hlist_empty(&rbconn->hhead))
250 gc_nodes[gc_count++] = rbconn;
251 }
252
253 if (gc_count) {
254 no_gc = true;
255 tree_nodes_free(root, gc_nodes, gc_count);
256 /* tree_node_free before new allocation permits
257 * allocator to re-use newly free'd object.
258 *
259 * This is a rare event; in most cases we will find
260 * existing node to re-use. (or gc_count is 0).
261 */
262 goto restart;
263 }
264
265 /* no match, need to insert new node */
266 rbconn = kmem_cache_alloc(connlimit_rb_cachep, GFP_ATOMIC);
267 if (rbconn == NULL)
268 return 0;
269
270 conn = kmem_cache_alloc(connlimit_conn_cachep, GFP_ATOMIC);
271 if (conn == NULL) {
272 kmem_cache_free(connlimit_rb_cachep, rbconn);
273 return 0;
274 }
275
276 conn->tuple = *tuple;
277 conn->addr = *addr;
278 rbconn->addr = *addr;
279
280 INIT_HLIST_HEAD(&rbconn->hhead);
281 hlist_add_head(&conn->node, &rbconn->hhead);
282
283 rb_link_node(&rbconn->node, parent, rbnode);
284 rb_insert_color(&rbconn->node, root);
285 return 1;
286 }
287
count_them(struct net * net,struct xt_connlimit_data * data,const struct nf_conntrack_tuple * tuple,const union nf_inet_addr * addr,const union nf_inet_addr * mask,u_int8_t family,u16 zone)288 static int count_them(struct net *net,
289 struct xt_connlimit_data *data,
290 const struct nf_conntrack_tuple *tuple,
291 const union nf_inet_addr *addr,
292 const union nf_inet_addr *mask,
293 u_int8_t family, u16 zone)
294 {
295 struct rb_root *root;
296 int count;
297 u32 hash;
298
299 if (family == NFPROTO_IPV6) {
300 hash = connlimit_iphash6(addr, mask);
301 root = &data->climit_root6[hash];
302 } else {
303 hash = connlimit_iphash(addr->ip & mask->ip);
304 root = &data->climit_root4[hash];
305 }
306
307 spin_lock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
308
309 count = count_tree(net, root, tuple, addr, mask, family, zone);
310
311 spin_unlock_bh(&xt_connlimit_locks[hash % CONNLIMIT_LOCK_SLOTS]);
312
313 return count;
314 }
315
316 static bool
connlimit_mt(const struct sk_buff * skb,struct xt_action_param * par)317 connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
318 {
319 struct net *net = dev_net(par->in ? par->in : par->out);
320 const struct xt_connlimit_info *info = par->matchinfo;
321 union nf_inet_addr addr;
322 struct nf_conntrack_tuple tuple;
323 const struct nf_conntrack_tuple *tuple_ptr = &tuple;
324 enum ip_conntrack_info ctinfo;
325 const struct nf_conn *ct;
326 unsigned int connections;
327 u16 zone = NF_CT_DEFAULT_ZONE;
328
329 ct = nf_ct_get(skb, &ctinfo);
330 if (ct != NULL) {
331 tuple_ptr = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
332 zone = nf_ct_zone(ct);
333 } else if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
334 par->family, &tuple)) {
335 goto hotdrop;
336 }
337
338 if (par->family == NFPROTO_IPV6) {
339 const struct ipv6hdr *iph = ipv6_hdr(skb);
340 memcpy(&addr.ip6, (info->flags & XT_CONNLIMIT_DADDR) ?
341 &iph->daddr : &iph->saddr, sizeof(addr.ip6));
342 } else {
343 const struct iphdr *iph = ip_hdr(skb);
344 addr.ip = (info->flags & XT_CONNLIMIT_DADDR) ?
345 iph->daddr : iph->saddr;
346 }
347
348 connections = count_them(net, info->data, tuple_ptr, &addr,
349 &info->mask, par->family, zone);
350 if (connections == 0)
351 /* kmalloc failed, drop it entirely */
352 goto hotdrop;
353
354 return (connections > info->limit) ^
355 !!(info->flags & XT_CONNLIMIT_INVERT);
356
357 hotdrop:
358 par->hotdrop = true;
359 return false;
360 }
361
connlimit_mt_check(const struct xt_mtchk_param * par)362 static int connlimit_mt_check(const struct xt_mtchk_param *par)
363 {
364 struct xt_connlimit_info *info = par->matchinfo;
365 unsigned int i;
366 int ret;
367
368 if (unlikely(!connlimit_rnd)) {
369 u_int32_t rand;
370
371 do {
372 get_random_bytes(&rand, sizeof(rand));
373 } while (!rand);
374 cmpxchg(&connlimit_rnd, 0, rand);
375 }
376 ret = nf_ct_l3proto_try_module_get(par->family);
377 if (ret < 0) {
378 pr_info("cannot load conntrack support for "
379 "address family %u\n", par->family);
380 return ret;
381 }
382
383 /* init private data */
384 info->data = kmalloc(sizeof(struct xt_connlimit_data), GFP_KERNEL);
385 if (info->data == NULL) {
386 nf_ct_l3proto_module_put(par->family);
387 return -ENOMEM;
388 }
389
390 for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
391 info->data->climit_root4[i] = RB_ROOT;
392 for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
393 info->data->climit_root6[i] = RB_ROOT;
394
395 return 0;
396 }
397
destroy_tree(struct rb_root * r)398 static void destroy_tree(struct rb_root *r)
399 {
400 struct xt_connlimit_conn *conn;
401 struct xt_connlimit_rb *rbconn;
402 struct hlist_node *n;
403 struct rb_node *node;
404
405 while ((node = rb_first(r)) != NULL) {
406 rbconn = container_of(node, struct xt_connlimit_rb, node);
407
408 rb_erase(node, r);
409
410 hlist_for_each_entry_safe(conn, n, &rbconn->hhead, node)
411 kmem_cache_free(connlimit_conn_cachep, conn);
412
413 kmem_cache_free(connlimit_rb_cachep, rbconn);
414 }
415 }
416
connlimit_mt_destroy(const struct xt_mtdtor_param * par)417 static void connlimit_mt_destroy(const struct xt_mtdtor_param *par)
418 {
419 const struct xt_connlimit_info *info = par->matchinfo;
420 unsigned int i;
421
422 nf_ct_l3proto_module_put(par->family);
423
424 for (i = 0; i < ARRAY_SIZE(info->data->climit_root4); ++i)
425 destroy_tree(&info->data->climit_root4[i]);
426 for (i = 0; i < ARRAY_SIZE(info->data->climit_root6); ++i)
427 destroy_tree(&info->data->climit_root6[i]);
428
429 kfree(info->data);
430 }
431
432 static struct xt_match connlimit_mt_reg __read_mostly = {
433 .name = "connlimit",
434 .revision = 1,
435 .family = NFPROTO_UNSPEC,
436 .checkentry = connlimit_mt_check,
437 .match = connlimit_mt,
438 .matchsize = sizeof(struct xt_connlimit_info),
439 .destroy = connlimit_mt_destroy,
440 .me = THIS_MODULE,
441 };
442
connlimit_mt_init(void)443 static int __init connlimit_mt_init(void)
444 {
445 int ret, i;
446
447 BUILD_BUG_ON(CONNLIMIT_LOCK_SLOTS > CONNLIMIT_SLOTS);
448 BUILD_BUG_ON((CONNLIMIT_SLOTS % CONNLIMIT_LOCK_SLOTS) != 0);
449
450 for (i = 0; i < CONNLIMIT_LOCK_SLOTS; ++i)
451 spin_lock_init(&xt_connlimit_locks[i]);
452
453 connlimit_conn_cachep = kmem_cache_create("xt_connlimit_conn",
454 sizeof(struct xt_connlimit_conn),
455 0, 0, NULL);
456 if (!connlimit_conn_cachep)
457 return -ENOMEM;
458
459 connlimit_rb_cachep = kmem_cache_create("xt_connlimit_rb",
460 sizeof(struct xt_connlimit_rb),
461 0, 0, NULL);
462 if (!connlimit_rb_cachep) {
463 kmem_cache_destroy(connlimit_conn_cachep);
464 return -ENOMEM;
465 }
466 ret = xt_register_match(&connlimit_mt_reg);
467 if (ret != 0) {
468 kmem_cache_destroy(connlimit_conn_cachep);
469 kmem_cache_destroy(connlimit_rb_cachep);
470 }
471 return ret;
472 }
473
connlimit_mt_exit(void)474 static void __exit connlimit_mt_exit(void)
475 {
476 xt_unregister_match(&connlimit_mt_reg);
477 kmem_cache_destroy(connlimit_conn_cachep);
478 kmem_cache_destroy(connlimit_rb_cachep);
479 }
480
481 module_init(connlimit_mt_init);
482 module_exit(connlimit_mt_exit);
483 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
484 MODULE_DESCRIPTION("Xtables: Number of connections matching");
485 MODULE_LICENSE("GPL");
486 MODULE_ALIAS("ipt_connlimit");
487 MODULE_ALIAS("ip6t_connlimit");
488