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-rw-r--r--net/ipv4/inetpeer.c460
1 files changed, 460 insertions, 0 deletions
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
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1/*
2 * INETPEER - A storage for permanent information about peers
3 *
4 * This source is covered by the GNU GPL, the same as all kernel sources.
5 *
6 * Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $
7 *
8 * Authors: Andrey V. Savochkin <saw@msu.ru>
9 */
10
11#include <linux/module.h>
12#include <linux/types.h>
13#include <linux/slab.h>
14#include <linux/interrupt.h>
15#include <linux/spinlock.h>
16#include <linux/random.h>
17#include <linux/sched.h>
18#include <linux/timer.h>
19#include <linux/time.h>
20#include <linux/kernel.h>
21#include <linux/mm.h>
22#include <linux/net.h>
23#include <net/inetpeer.h>
24
25/*
26 * Theory of operations.
27 * We keep one entry for each peer IP address. The nodes contains long-living
28 * information about the peer which doesn't depend on routes.
29 * At this moment this information consists only of ID field for the next
30 * outgoing IP packet. This field is incremented with each packet as encoded
31 * in inet_getid() function (include/net/inetpeer.h).
32 * At the moment of writing this notes identifier of IP packets is generated
33 * to be unpredictable using this code only for packets subjected
34 * (actually or potentially) to defragmentation. I.e. DF packets less than
35 * PMTU in size uses a constant ID and do not use this code (see
36 * ip_select_ident() in include/net/ip.h).
37 *
38 * Route cache entries hold references to our nodes.
39 * New cache entries get references via lookup by destination IP address in
40 * the avl tree. The reference is grabbed only when it's needed i.e. only
41 * when we try to output IP packet which needs an unpredictable ID (see
42 * __ip_select_ident() in net/ipv4/route.c).
43 * Nodes are removed only when reference counter goes to 0.
44 * When it's happened the node may be removed when a sufficient amount of
45 * time has been passed since its last use. The less-recently-used entry can
46 * also be removed if the pool is overloaded i.e. if the total amount of
47 * entries is greater-or-equal than the threshold.
48 *
49 * Node pool is organised as an AVL tree.
50 * Such an implementation has been chosen not just for fun. It's a way to
51 * prevent easy and efficient DoS attacks by creating hash collisions. A huge
52 * amount of long living nodes in a single hash slot would significantly delay
53 * lookups performed with disabled BHs.
54 *
55 * Serialisation issues.
56 * 1. Nodes may appear in the tree only with the pool write lock held.
57 * 2. Nodes may disappear from the tree only with the pool write lock held
58 * AND reference count being 0.
59 * 3. Nodes appears and disappears from unused node list only under
60 * "inet_peer_unused_lock".
61 * 4. Global variable peer_total is modified under the pool lock.
62 * 5. struct inet_peer fields modification:
63 * avl_left, avl_right, avl_parent, avl_height: pool lock
64 * unused_next, unused_prevp: unused node list lock
65 * refcnt: atomically against modifications on other CPU;
66 * usually under some other lock to prevent node disappearing
67 * dtime: unused node list lock
68 * v4daddr: unchangeable
69 * ip_id_count: idlock
70 */
71
72/* Exported for inet_getid inline function. */
73DEFINE_SPINLOCK(inet_peer_idlock);
74
75static kmem_cache_t *peer_cachep;
76
77#define node_height(x) x->avl_height
78static struct inet_peer peer_fake_node = {
79 .avl_left = &peer_fake_node,
80 .avl_right = &peer_fake_node,
81 .avl_height = 0
82};
83#define peer_avl_empty (&peer_fake_node)
84static struct inet_peer *peer_root = peer_avl_empty;
85static DEFINE_RWLOCK(peer_pool_lock);
86#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
87
88static volatile int peer_total;
89/* Exported for sysctl_net_ipv4. */
90int inet_peer_threshold = 65536 + 128; /* start to throw entries more
91 * aggressively at this stage */
92int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */
93int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */
94
95static struct inet_peer *inet_peer_unused_head;
96/* Exported for inet_putpeer inline function. */
97struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head;
98DEFINE_SPINLOCK(inet_peer_unused_lock);
99#define PEER_MAX_CLEANUP_WORK 30
100
101static void peer_check_expire(unsigned long dummy);
102static struct timer_list peer_periodic_timer =
103 TIMER_INITIALIZER(peer_check_expire, 0, 0);
104
105/* Exported for sysctl_net_ipv4. */
106int inet_peer_gc_mintime = 10 * HZ,
107 inet_peer_gc_maxtime = 120 * HZ;
108
109/* Called from ip_output.c:ip_init */
110void __init inet_initpeers(void)
111{
112 struct sysinfo si;
113
114 /* Use the straight interface to information about memory. */
115 si_meminfo(&si);
116 /* The values below were suggested by Alexey Kuznetsov
117 * <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
118 * myself. --SAW
119 */
120 if (si.totalram <= (32768*1024)/PAGE_SIZE)
121 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
122 if (si.totalram <= (16384*1024)/PAGE_SIZE)
123 inet_peer_threshold >>= 1; /* about 512KB */
124 if (si.totalram <= (8192*1024)/PAGE_SIZE)
125 inet_peer_threshold >>= 2; /* about 128KB */
126
127 peer_cachep = kmem_cache_create("inet_peer_cache",
128 sizeof(struct inet_peer),
129 0, SLAB_HWCACHE_ALIGN,
130 NULL, NULL);
131
132 if (!peer_cachep)
133 panic("cannot create inet_peer_cache");
134
135 /* All the timers, started at system startup tend
136 to synchronize. Perturb it a bit.
137 */
138 peer_periodic_timer.expires = jiffies
139 + net_random() % inet_peer_gc_maxtime
140 + inet_peer_gc_maxtime;
141 add_timer(&peer_periodic_timer);
142}
143
144/* Called with or without local BH being disabled. */
145static void unlink_from_unused(struct inet_peer *p)
146{
147 spin_lock_bh(&inet_peer_unused_lock);
148 if (p->unused_prevp != NULL) {
149 /* On unused list. */
150 *p->unused_prevp = p->unused_next;
151 if (p->unused_next != NULL)
152 p->unused_next->unused_prevp = p->unused_prevp;
153 else
154 inet_peer_unused_tailp = p->unused_prevp;
155 p->unused_prevp = NULL; /* mark it as removed */
156 }
157 spin_unlock_bh(&inet_peer_unused_lock);
158}
159
160/* Called with local BH disabled and the pool lock held. */
161#define lookup(daddr) \
162({ \
163 struct inet_peer *u, **v; \
164 stackptr = stack; \
165 *stackptr++ = &peer_root; \
166 for (u = peer_root; u != peer_avl_empty; ) { \
167 if (daddr == u->v4daddr) \
168 break; \
169 if (daddr < u->v4daddr) \
170 v = &u->avl_left; \
171 else \
172 v = &u->avl_right; \
173 *stackptr++ = v; \
174 u = *v; \
175 } \
176 u; \
177})
178
179/* Called with local BH disabled and the pool write lock held. */
180#define lookup_rightempty(start) \
181({ \
182 struct inet_peer *u, **v; \
183 *stackptr++ = &start->avl_left; \
184 v = &start->avl_left; \
185 for (u = *v; u->avl_right != peer_avl_empty; ) { \
186 v = &u->avl_right; \
187 *stackptr++ = v; \
188 u = *v; \
189 } \
190 u; \
191})
192
193/* Called with local BH disabled and the pool write lock held.
194 * Variable names are the proof of operation correctness.
195 * Look into mm/map_avl.c for more detail description of the ideas. */
196static void peer_avl_rebalance(struct inet_peer **stack[],
197 struct inet_peer ***stackend)
198{
199 struct inet_peer **nodep, *node, *l, *r;
200 int lh, rh;
201
202 while (stackend > stack) {
203 nodep = *--stackend;
204 node = *nodep;
205 l = node->avl_left;
206 r = node->avl_right;
207 lh = node_height(l);
208 rh = node_height(r);
209 if (lh > rh + 1) { /* l: RH+2 */
210 struct inet_peer *ll, *lr, *lrl, *lrr;
211 int lrh;
212 ll = l->avl_left;
213 lr = l->avl_right;
214 lrh = node_height(lr);
215 if (lrh <= node_height(ll)) { /* ll: RH+1 */
216 node->avl_left = lr; /* lr: RH or RH+1 */
217 node->avl_right = r; /* r: RH */
218 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
219 l->avl_left = ll; /* ll: RH+1 */
220 l->avl_right = node; /* node: RH+1 or RH+2 */
221 l->avl_height = node->avl_height + 1;
222 *nodep = l;
223 } else { /* ll: RH, lr: RH+1 */
224 lrl = lr->avl_left; /* lrl: RH or RH-1 */
225 lrr = lr->avl_right; /* lrr: RH or RH-1 */
226 node->avl_left = lrr; /* lrr: RH or RH-1 */
227 node->avl_right = r; /* r: RH */
228 node->avl_height = rh + 1; /* node: RH+1 */
229 l->avl_left = ll; /* ll: RH */
230 l->avl_right = lrl; /* lrl: RH or RH-1 */
231 l->avl_height = rh + 1; /* l: RH+1 */
232 lr->avl_left = l; /* l: RH+1 */
233 lr->avl_right = node; /* node: RH+1 */
234 lr->avl_height = rh + 2;
235 *nodep = lr;
236 }
237 } else if (rh > lh + 1) { /* r: LH+2 */
238 struct inet_peer *rr, *rl, *rlr, *rll;
239 int rlh;
240 rr = r->avl_right;
241 rl = r->avl_left;
242 rlh = node_height(rl);
243 if (rlh <= node_height(rr)) { /* rr: LH+1 */
244 node->avl_right = rl; /* rl: LH or LH+1 */
245 node->avl_left = l; /* l: LH */
246 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
247 r->avl_right = rr; /* rr: LH+1 */
248 r->avl_left = node; /* node: LH+1 or LH+2 */
249 r->avl_height = node->avl_height + 1;
250 *nodep = r;
251 } else { /* rr: RH, rl: RH+1 */
252 rlr = rl->avl_right; /* rlr: LH or LH-1 */
253 rll = rl->avl_left; /* rll: LH or LH-1 */
254 node->avl_right = rll; /* rll: LH or LH-1 */
255 node->avl_left = l; /* l: LH */
256 node->avl_height = lh + 1; /* node: LH+1 */
257 r->avl_right = rr; /* rr: LH */
258 r->avl_left = rlr; /* rlr: LH or LH-1 */
259 r->avl_height = lh + 1; /* r: LH+1 */
260 rl->avl_right = r; /* r: LH+1 */
261 rl->avl_left = node; /* node: LH+1 */
262 rl->avl_height = lh + 2;
263 *nodep = rl;
264 }
265 } else {
266 node->avl_height = (lh > rh ? lh : rh) + 1;
267 }
268 }
269}
270
271/* Called with local BH disabled and the pool write lock held. */
272#define link_to_pool(n) \
273do { \
274 n->avl_height = 1; \
275 n->avl_left = peer_avl_empty; \
276 n->avl_right = peer_avl_empty; \
277 **--stackptr = n; \
278 peer_avl_rebalance(stack, stackptr); \
279} while(0)
280
281/* May be called with local BH enabled. */
282static void unlink_from_pool(struct inet_peer *p)
283{
284 int do_free;
285
286 do_free = 0;
287
288 write_lock_bh(&peer_pool_lock);
289 /* Check the reference counter. It was artificially incremented by 1
290 * in cleanup() function to prevent sudden disappearing. If the
291 * reference count is still 1 then the node is referenced only as `p'
292 * here and from the pool. So under the exclusive pool lock it's safe
293 * to remove the node and free it later. */
294 if (atomic_read(&p->refcnt) == 1) {
295 struct inet_peer **stack[PEER_MAXDEPTH];
296 struct inet_peer ***stackptr, ***delp;
297 if (lookup(p->v4daddr) != p)
298 BUG();
299 delp = stackptr - 1; /* *delp[0] == p */
300 if (p->avl_left == peer_avl_empty) {
301 *delp[0] = p->avl_right;
302 --stackptr;
303 } else {
304 /* look for a node to insert instead of p */
305 struct inet_peer *t;
306 t = lookup_rightempty(p);
307 if (*stackptr[-1] != t)
308 BUG();
309 **--stackptr = t->avl_left;
310 /* t is removed, t->v4daddr > x->v4daddr for any
311 * x in p->avl_left subtree.
312 * Put t in the old place of p. */
313 *delp[0] = t;
314 t->avl_left = p->avl_left;
315 t->avl_right = p->avl_right;
316 t->avl_height = p->avl_height;
317 if (delp[1] != &p->avl_left)
318 BUG();
319 delp[1] = &t->avl_left; /* was &p->avl_left */
320 }
321 peer_avl_rebalance(stack, stackptr);
322 peer_total--;
323 do_free = 1;
324 }
325 write_unlock_bh(&peer_pool_lock);
326
327 if (do_free)
328 kmem_cache_free(peer_cachep, p);
329 else
330 /* The node is used again. Decrease the reference counter
331 * back. The loop "cleanup -> unlink_from_unused
332 * -> unlink_from_pool -> putpeer -> link_to_unused
333 * -> cleanup (for the same node)"
334 * doesn't really exist because the entry will have a
335 * recent deletion time and will not be cleaned again soon. */
336 inet_putpeer(p);
337}
338
339/* May be called with local BH enabled. */
340static int cleanup_once(unsigned long ttl)
341{
342 struct inet_peer *p;
343
344 /* Remove the first entry from the list of unused nodes. */
345 spin_lock_bh(&inet_peer_unused_lock);
346 p = inet_peer_unused_head;
347 if (p != NULL) {
348 if (time_after(p->dtime + ttl, jiffies)) {
349 /* Do not prune fresh entries. */
350 spin_unlock_bh(&inet_peer_unused_lock);
351 return -1;
352 }
353 inet_peer_unused_head = p->unused_next;
354 if (p->unused_next != NULL)
355 p->unused_next->unused_prevp = p->unused_prevp;
356 else
357 inet_peer_unused_tailp = p->unused_prevp;
358 p->unused_prevp = NULL; /* mark as not on the list */
359 /* Grab an extra reference to prevent node disappearing
360 * before unlink_from_pool() call. */
361 atomic_inc(&p->refcnt);
362 }
363 spin_unlock_bh(&inet_peer_unused_lock);
364
365 if (p == NULL)
366 /* It means that the total number of USED entries has
367 * grown over inet_peer_threshold. It shouldn't really
368 * happen because of entry limits in route cache. */
369 return -1;
370
371 unlink_from_pool(p);
372 return 0;
373}
374
375/* Called with or without local BH being disabled. */
376struct inet_peer *inet_getpeer(__u32 daddr, int create)
377{
378 struct inet_peer *p, *n;
379 struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
380
381 /* Look up for the address quickly. */
382 read_lock_bh(&peer_pool_lock);
383 p = lookup(daddr);
384 if (p != peer_avl_empty)
385 atomic_inc(&p->refcnt);
386 read_unlock_bh(&peer_pool_lock);
387
388 if (p != peer_avl_empty) {
389 /* The existing node has been found. */
390 /* Remove the entry from unused list if it was there. */
391 unlink_from_unused(p);
392 return p;
393 }
394
395 if (!create)
396 return NULL;
397
398 /* Allocate the space outside the locked region. */
399 n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
400 if (n == NULL)
401 return NULL;
402 n->v4daddr = daddr;
403 atomic_set(&n->refcnt, 1);
404 n->ip_id_count = secure_ip_id(daddr);
405 n->tcp_ts_stamp = 0;
406
407 write_lock_bh(&peer_pool_lock);
408 /* Check if an entry has suddenly appeared. */
409 p = lookup(daddr);
410 if (p != peer_avl_empty)
411 goto out_free;
412
413 /* Link the node. */
414 link_to_pool(n);
415 n->unused_prevp = NULL; /* not on the list */
416 peer_total++;
417 write_unlock_bh(&peer_pool_lock);
418
419 if (peer_total >= inet_peer_threshold)
420 /* Remove one less-recently-used entry. */
421 cleanup_once(0);
422
423 return n;
424
425out_free:
426 /* The appropriate node is already in the pool. */
427 atomic_inc(&p->refcnt);
428 write_unlock_bh(&peer_pool_lock);
429 /* Remove the entry from unused list if it was there. */
430 unlink_from_unused(p);
431 /* Free preallocated the preallocated node. */
432 kmem_cache_free(peer_cachep, n);
433 return p;
434}
435
436/* Called with local BH disabled. */
437static void peer_check_expire(unsigned long dummy)
438{
439 int i;
440 int ttl;
441
442 if (peer_total >= inet_peer_threshold)
443 ttl = inet_peer_minttl;
444 else
445 ttl = inet_peer_maxttl
446 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
447 peer_total / inet_peer_threshold * HZ;
448 for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++);
449
450 /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
451 * interval depending on the total number of entries (more entries,
452 * less interval). */
453 peer_periodic_timer.expires = jiffies
454 + inet_peer_gc_maxtime
455 - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
456 peer_total / inet_peer_threshold * HZ;
457 add_timer(&peer_periodic_timer);
458}
459
460EXPORT_SYMBOL(inet_peer_idlock);
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