aboutsummaryrefslogtreecommitdiffstats
path: root/net/ipv4/inetpeer.c
blob: a456ceeac3f22519e5bac707a6c57d110c89e79a (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
/*
 *		INETPEER - A storage for permanent information about peers
 *
 *  This source is covered by the GNU GPL, the same as all kernel sources.
 *
 *  Authors:	Andrey V. Savochkin <saw@msu.ru>
 */

#include <linux/module.h>
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/random.h>
#include <linux/timer.h>
#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/net.h>
#include <net/ip.h>
#include <net/inetpeer.h>

/*
 *  Theory of operations.
 *  We keep one entry for each peer IP address.  The nodes contains long-living
 *  information about the peer which doesn't depend on routes.
 *  At this moment this information consists only of ID field for the next
 *  outgoing IP packet.  This field is incremented with each packet as encoded
 *  in inet_getid() function (include/net/inetpeer.h).
 *  At the moment of writing this notes identifier of IP packets is generated
 *  to be unpredictable using this code only for packets subjected
 *  (actually or potentially) to defragmentation.  I.e. DF packets less than
 *  PMTU in size uses a constant ID and do not use this code (see
 *  ip_select_ident() in include/net/ip.h).
 *
 *  Route cache entries hold references to our nodes.
 *  New cache entries get references via lookup by destination IP address in
 *  the avl tree.  The reference is grabbed only when it's needed i.e. only
 *  when we try to output IP packet which needs an unpredictable ID (see
 *  __ip_select_ident() in net/ipv4/route.c).
 *  Nodes are removed only when reference counter goes to 0.
 *  When it's happened the node may be removed when a sufficient amount of
 *  time has been passed since its last use.  The less-recently-used entry can
 *  also be removed if the pool is overloaded i.e. if the total amount of
 *  entries is greater-or-equal than the threshold.
 *
 *  Node pool is organised as an AVL tree.
 *  Such an implementation has been chosen not just for fun.  It's a way to
 *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge
 *  amount of long living nodes in a single hash slot would significantly delay
 *  lookups performed with disabled BHs.
 *
 *  Serialisation issues.
 *  1.  Nodes may appear in the tree only with the pool write lock held.
 *  2.  Nodes may disappear from the tree only with the pool write lock held
 *      AND reference count being 0.
 *  3.  Nodes appears and disappears from unused node list only under
 *      "inet_peer_unused_lock".
 *  4.  Global variable peer_total is modified under the pool lock.
 *  5.  struct inet_peer fields modification:
 *		avl_left, avl_right, avl_parent, avl_height: pool lock
 *		unused: unused node list lock
 *		refcnt: atomically against modifications on other CPU;
 *		   usually under some other lock to prevent node disappearing
 *		dtime: unused node list lock
 *		v4daddr: unchangeable
 *		ip_id_count: idlock
 */

/* Exported for inet_getid inline function.  */
DEFINE_SPINLOCK(inet_peer_idlock);

static struct kmem_cache *peer_cachep __read_mostly;

#define node_height(x) x->avl_height
static struct inet_peer peer_fake_node = {
	.avl_left	= &peer_fake_node,
	.avl_right	= &peer_fake_node,
	.avl_height	= 0
};
#define peer_avl_empty (&peer_fake_node)
static struct inet_peer *peer_root = peer_avl_empty;
static DEFINE_RWLOCK(peer_pool_lock);
#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */

static int peer_total;
/* Exported for sysctl_net_ipv4.  */
int inet_peer_threshold __read_mostly = 65536 + 128;	/* start to throw entries more
					 * aggressively at this stage */
int inet_peer_minttl __read_mostly = 120 * HZ;	/* TTL under high load: 120 sec */
int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;	/* usual time to live: 10 min */
int inet_peer_gc_mintime __read_mostly = 10 * HZ;
int inet_peer_gc_maxtime __read_mostly = 120 * HZ;

static LIST_HEAD(unused_peers);
static DEFINE_SPINLOCK(inet_peer_unused_lock);

static void peer_check_expire(unsigned long dummy);
static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);


/* Called from ip_output.c:ip_init  */
void __init inet_initpeers(void)
{
	struct sysinfo si;

	/* Use the straight interface to information about memory. */
	si_meminfo(&si);
	/* The values below were suggested by Alexey Kuznetsov
	 * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
	 * myself.  --SAW
	 */
	if (si.totalram <= (32768*1024)/PAGE_SIZE)
		inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
	if (si.totalram <= (16384*1024)/PAGE_SIZE)
		inet_peer_threshold >>= 1; /* about 512KB */
	if (si.totalram <= (8192*1024)/PAGE_SIZE)
		inet_peer_threshold >>= 2; /* about 128KB */

	peer_cachep = kmem_cache_create("inet_peer_cache",
			sizeof(struct inet_peer),
			0, SLAB_HWCACHE_ALIGN|SLAB_PANIC,
			NULL);

	/* All the timers, started at system startup tend
	   to synchronize. Perturb it a bit.
	 */
	peer_periodic_timer.expires = jiffies
		+ net_random() % inet_peer_gc_maxtime
		+ inet_peer_gc_maxtime;
	add_timer(&peer_periodic_timer);
}

/* Called with or without local BH being disabled. */
static void unlink_from_unused(struct inet_peer *p)
{
	spin_lock_bh(&inet_peer_unused_lock);
	list_del_init(&p->unused);
	spin_unlock_bh(&inet_peer_unused_lock);
}

/*
 * Called with local BH disabled and the pool lock held.
 * _stack is known to be NULL or not at compile time,
 * so compiler will optimize the if (_stack) tests.
 */
#define lookup(_daddr,_stack) 					\
({								\
	struct inet_peer *u, **v;				\
	if (_stack != NULL) {					\
		stackptr = _stack;				\
		*stackptr++ = &peer_root;			\
	}							\
	for (u = peer_root; u != peer_avl_empty; ) {		\
		if (_daddr == u->v4daddr)			\
			break;					\
		if ((__force __u32)_daddr < (__force __u32)u->v4daddr)	\
			v = &u->avl_left;			\
		else						\
			v = &u->avl_right;			\
		if (_stack != NULL)				\
			*stackptr++ = v;			\
		u = *v;						\
	}							\
	u;							\
})

/* Called with local BH disabled and the pool write lock held. */
#define lookup_rightempty(start)				\
({								\
	struct inet_peer *u, **v;				\
	*stackptr++ = &start->avl_left;				\
	v = &start->avl_left;					\
	for (u = *v; u->avl_right != peer_avl_empty; ) {	\
		v = &u->avl_right;				\
		*stackptr++ = v;				\
		u = *v;						\
	}							\
	u;							\
})

/* Called with local BH disabled and the pool write lock held.
 * Variable names are the proof of operation correctness.
 * Look into mm/map_avl.c for more detail description of the ideas.  */
static void peer_avl_rebalance(struct inet_peer **stack[],
		struct inet_peer ***stackend)
{
	struct inet_peer **nodep, *node, *l, *r;
	int lh, rh;

	while (stackend > stack) {
		nodep = *--stackend;
		node = *nodep;
		l = node->avl_left;
		r = node->avl_right;
		lh = node_height(l);
		rh = node_height(r);
		if (lh > rh + 1) { /* l: RH+2 */
			struct inet_peer *ll, *lr, *lrl, *lrr;
			int lrh;
			ll = l->avl_left;
			lr = l->avl_right;
			lrh = node_height(lr);
			if (lrh <= node_height(ll)) {	/* ll: RH+1 */
				node->avl_left = lr;	/* lr: RH or RH+1 */
				node->avl_right = r;	/* r: RH */
				node->avl_height = lrh + 1; /* RH+1 or RH+2 */
				l->avl_left = ll;	/* ll: RH+1 */
				l->avl_right = node;	/* node: RH+1 or RH+2 */
				l->avl_height = node->avl_height + 1;
				*nodep = l;
			} else { /* ll: RH, lr: RH+1 */
				lrl = lr->avl_left;	/* lrl: RH or RH-1 */
				lrr = lr->avl_right;	/* lrr: RH or RH-1 */
				node->avl_left = lrr;	/* lrr: RH or RH-1 */
				node->avl_right = r;	/* r: RH */
				node->avl_height = rh + 1; /* node: RH+1 */
				l->avl_left = ll;	/* ll: RH */
				l->avl_right = lrl;	/* lrl: RH or RH-1 */
				l->avl_height = rh + 1;	/* l: RH+1 */
				lr->avl_left = l;	/* l: RH+1 */
				lr->avl_right = node;	/* node: RH+1 */
				lr->avl_height = rh + 2;
				*nodep = lr;
			}
		} else if (rh > lh + 1) { /* r: LH+2 */
			struct inet_peer *rr, *rl, *rlr, *rll;
			int rlh;
			rr = r->avl_right;
			rl = r->avl_left;
			rlh = node_height(rl);
			if (rlh <= node_height(rr)) {	/* rr: LH+1 */
				node->avl_right = rl;	/* rl: LH or LH+1 */
				node->avl_left = l;	/* l: LH */
				node->avl_height = rlh + 1; /* LH+1 or LH+2 */
				r->avl_right = rr;	/* rr: LH+1 */
				r->avl_left = node;	/* node: LH+1 or LH+2 */
				r->avl_height = node->avl_height + 1;
				*nodep = r;
			} else { /* rr: RH, rl: RH+1 */
				rlr = rl->avl_right;	/* rlr: LH or LH-1 */
				rll = rl->avl_left;	/* rll: LH or LH-1 */
				node->avl_right = rll;	/* rll: LH or LH-1 */
				node->avl_left = l;	/* l: LH */
				node->avl_height = lh + 1; /* node: LH+1 */
				r->avl_right = rr;	/* rr: LH */
				r->avl_left = rlr;	/* rlr: LH or LH-1 */
				r->avl_height = lh + 1;	/* r: LH+1 */
				rl->avl_right = r;	/* r: LH+1 */
				rl->avl_left = node;	/* node: LH+1 */
				rl->avl_height = lh + 2;
				*nodep = rl;
			}
		} else {
			node->avl_height = (lh > rh ? lh : rh) + 1;
		}
	}
}

/* Called with local BH disabled and the pool write lock held. */
#define link_to_pool(n)						\
do {								\
	n->avl_height = 1;					\
	n->avl_left = peer_avl_empty;				\
	n->avl_right = peer_avl_empty;				\
	**--stackptr = n;					\
	peer_avl_rebalance(stack, stackptr);			\
} while(0)

/* May be called with local BH enabled. */
static void unlink_from_pool(struct inet_peer *p)
{
	int do_free;

	do_free = 0;

	write_lock_bh(&peer_pool_lock);
	/* Check the reference counter.  It was artificially incremented by 1
	 * in cleanup() function to prevent sudden disappearing.  If the
	 * reference count is still 1 then the node is referenced only as `p'
	 * here and from the pool.  So under the exclusive pool lock it's safe
	 * to remove the node and free it later. */
	if (atomic_read(&p->refcnt) == 1) {
		struct inet_peer **stack[PEER_MAXDEPTH];
		struct inet_peer ***stackptr, ***delp;
		if (lookup(p->v4daddr, stack) != p)
			BUG();
		delp = stackptr - 1; /* *delp[0] == p */
		if (p->avl_left == peer_avl_empty) {
			*delp[0] = p->avl_right;
			--stackptr;
		} else {
			/* look for a node to insert instead of p */
			struct inet_peer *t;
			t = lookup_rightempty(p);
			BUG_ON(*stackptr[-1] != t);
			**--stackptr = t->avl_left;
			/* t is removed, t->v4daddr > x->v4daddr for any
			 * x in p->avl_left subtree.
			 * Put t in the old place of p. */
			*delp[0] = t;
			t->avl_left = p->avl_left;
			t->avl_right = p->avl_right;
			t->avl_height = p->avl_height;
			BUG_ON(delp[1] != &p->avl_left);
			delp[1] = &t->avl_left; /* was &p->avl_left */
		}
		peer_avl_rebalance(stack, stackptr);
		peer_total--;
		do_free = 1;
	}
	write_unlock_bh(&peer_pool_lock);

	if (do_free)
		kmem_cache_free(peer_cachep, p);
	else
		/* The node is used again.  Decrease the reference counter
		 * back.  The loop "cleanup -> unlink_from_unused
		 *   -> unlink_from_pool -> putpeer -> link_to_unused
		 *   -> cleanup (for the same node)"
		 * doesn't really exist because the entry will have a
		 * recent deletion time and will not be cleaned again soon. */
		inet_putpeer(p);
}

/* May be called with local BH enabled. */
static int cleanup_once(unsigned long ttl)
{
	struct inet_peer *p = NULL;

	/* Remove the first entry from the list of unused nodes. */
	spin_lock_bh(&inet_peer_unused_lock);
	if (!list_empty(&unused_peers)) {
		__u32 delta;

		p = list_first_entry(&unused_peers, struct inet_peer, unused);
		delta = (__u32)jiffies - p->dtime;

		if (delta < ttl) {
			/* Do not prune fresh entries. */
			spin_unlock_bh(&inet_peer_unused_lock);
			return -1;
		}

		list_del_init(&p->unused);

		/* Grab an extra reference to prevent node disappearing
		 * before unlink_from_pool() call. */
		atomic_inc(&p->refcnt);
	}
	spin_unlock_bh(&inet_peer_unused_lock);

	if (p == NULL)
		/* It means that the total number of USED entries has
		 * grown over inet_peer_threshold.  It shouldn't really
		 * happen because of entry limits in route cache. */
		return -1;

	unlink_from_pool(p);
	return 0;
}

/* Called with or without local BH being disabled. */
struct inet_peer *inet_getpeer(__be32 daddr, int create)
{
	struct inet_peer *p, *n;
	struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;

	/* Look up for the address quickly. */
	read_lock_bh(&peer_pool_lock);
	p = lookup(daddr, NULL);
	if (p != peer_avl_empty)
		atomic_inc(&p->refcnt);
	read_unlock_bh(&peer_pool_lock);

	if (p != peer_avl_empty) {
		/* The existing node has been found. */
		/* Remove the entry from unused list if it was there. */
		unlink_from_unused(p);
		return p;
	}

	if (!create)
		return NULL;

	/* Allocate the space outside the locked region. */
	n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
	if (n == NULL)
		return NULL;
	n->v4daddr = daddr;
	atomic_set(&n->refcnt, 1);
	atomic_set(&n->rid, 0);
	n->ip_id_count = secure_ip_id(daddr);
	n->tcp_ts_stamp = 0;

	write_lock_bh(&peer_pool_lock);
	/* Check if an entry has suddenly appeared. */
	p = lookup(daddr, stack);
	if (p != peer_avl_empty)
		goto out_free;

	/* Link the node. */
	link_to_pool(n);
	INIT_LIST_HEAD(&n->unused);
	peer_total++;
	write_unlock_bh(&peer_pool_lock);

	if (peer_total >= inet_peer_threshold)
		/* Remove one less-recently-used entry. */
		cleanup_once(0);

	return n;

out_free:
	/* The appropriate node is already in the pool. */
	atomic_inc(&p->refcnt);
	write_unlock_bh(&peer_pool_lock);
	/* Remove the entry from unused list if it was there. */
	unlink_from_unused(p);
	/* Free preallocated the preallocated node. */
	kmem_cache_free(peer_cachep, n);
	return p;
}

/* Called with local BH disabled. */
static void peer_check_expire(unsigned long dummy)
{
	unsigned long now = jiffies;
	int ttl;

	if (peer_total >= inet_peer_threshold)
		ttl = inet_peer_minttl;
	else
		ttl = inet_peer_maxttl
				- (inet_peer_maxttl - inet_peer_minttl) / HZ *
					peer_total / inet_peer_threshold * HZ;
	while (!cleanup_once(ttl)) {
		if (jiffies != now)
			break;
	}

	/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
	 * interval depending on the total number of entries (more entries,
	 * less interval). */
	if (peer_total >= inet_peer_threshold)
		peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
	else
		peer_periodic_timer.expires = jiffies
			+ inet_peer_gc_maxtime
			- (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
				peer_total / inet_peer_threshold * HZ;
	add_timer(&peer_periodic_timer);
}

void inet_putpeer(struct inet_peer *p)
{
	spin_lock_bh(&inet_peer_unused_lock);
	if (atomic_dec_and_test(&p->refcnt)) {
		list_add_tail(&p->unused, &unused_peers);
		p->dtime = (__u32)jiffies;
	}
	spin_unlock_bh(&inet_peer_unused_lock);
}