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TOMOYO Linux Cross Reference
Linux/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  *  Authors:    Andrey V. Savochkin <saw@msu.ru>
  7  */
  8 
  9 #include <linux/module.h>
 10 #include <linux/types.h>
 11 #include <linux/slab.h>
 12 #include <linux/interrupt.h>
 13 #include <linux/spinlock.h>
 14 #include <linux/random.h>
 15 #include <linux/timer.h>
 16 #include <linux/time.h>
 17 #include <linux/kernel.h>
 18 #include <linux/mm.h>
 19 #include <linux/net.h>
 20 #include <linux/workqueue.h>
 21 #include <net/ip.h>
 22 #include <net/inetpeer.h>
 23 #include <net/secure_seq.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  *
 30  *  Nodes are removed only when reference counter goes to 0.
 31  *  When it's happened the node may be removed when a sufficient amount of
 32  *  time has been passed since its last use.  The less-recently-used entry can
 33  *  also be removed if the pool is overloaded i.e. if the total amount of
 34  *  entries is greater-or-equal than the threshold.
 35  *
 36  *  Node pool is organised as an AVL tree.
 37  *  Such an implementation has been chosen not just for fun.  It's a way to
 38  *  prevent easy and efficient DoS attacks by creating hash collisions.  A huge
 39  *  amount of long living nodes in a single hash slot would significantly delay
 40  *  lookups performed with disabled BHs.
 41  *
 42  *  Serialisation issues.
 43  *  1.  Nodes may appear in the tree only with the pool lock held.
 44  *  2.  Nodes may disappear from the tree only with the pool lock held
 45  *      AND reference count being 0.
 46  *  3.  Global variable peer_total is modified under the pool lock.
 47  *  4.  struct inet_peer fields modification:
 48  *              avl_left, avl_right, avl_parent, avl_height: pool lock
 49  *              refcnt: atomically against modifications on other CPU;
 50  *                 usually under some other lock to prevent node disappearing
 51  *              daddr: unchangeable
 52  */
 53 
 54 static struct kmem_cache *peer_cachep __read_mostly;
 55 
 56 static LIST_HEAD(gc_list);
 57 static const int gc_delay = 60 * HZ;
 58 static struct delayed_work gc_work;
 59 static DEFINE_SPINLOCK(gc_lock);
 60 
 61 #define node_height(x) x->avl_height
 62 
 63 #define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
 64 #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
 65 static const struct inet_peer peer_fake_node = {
 66         .avl_left       = peer_avl_empty_rcu,
 67         .avl_right      = peer_avl_empty_rcu,
 68         .avl_height     = 0
 69 };
 70 
 71 void inet_peer_base_init(struct inet_peer_base *bp)
 72 {
 73         bp->root = peer_avl_empty_rcu;
 74         seqlock_init(&bp->lock);
 75         bp->total = 0;
 76 }
 77 EXPORT_SYMBOL_GPL(inet_peer_base_init);
 78 
 79 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
 80 
 81 /* Exported for sysctl_net_ipv4.  */
 82 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
 83                                          * aggressively at this stage */
 84 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
 85 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
 86 
 87 static void inetpeer_gc_worker(struct work_struct *work)
 88 {
 89         struct inet_peer *p, *n, *c;
 90         struct list_head list;
 91 
 92         spin_lock_bh(&gc_lock);
 93         list_replace_init(&gc_list, &list);
 94         spin_unlock_bh(&gc_lock);
 95 
 96         if (list_empty(&list))
 97                 return;
 98 
 99         list_for_each_entry_safe(p, n, &list, gc_list) {
100 
101                 if (need_resched())
102                         cond_resched();
103 
104                 c = rcu_dereference_protected(p->avl_left, 1);
105                 if (c != peer_avl_empty) {
106                         list_add_tail(&c->gc_list, &list);
107                         p->avl_left = peer_avl_empty_rcu;
108                 }
109 
110                 c = rcu_dereference_protected(p->avl_right, 1);
111                 if (c != peer_avl_empty) {
112                         list_add_tail(&c->gc_list, &list);
113                         p->avl_right = peer_avl_empty_rcu;
114                 }
115 
116                 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
117 
118                 if (!atomic_read(&p->refcnt)) {
119                         list_del(&p->gc_list);
120                         kmem_cache_free(peer_cachep, p);
121                 }
122         }
123 
124         if (list_empty(&list))
125                 return;
126 
127         spin_lock_bh(&gc_lock);
128         list_splice(&list, &gc_list);
129         spin_unlock_bh(&gc_lock);
130 
131         schedule_delayed_work(&gc_work, gc_delay);
132 }
133 
134 /* Called from ip_output.c:ip_init  */
135 void __init inet_initpeers(void)
136 {
137         struct sysinfo si;
138 
139         /* Use the straight interface to information about memory. */
140         si_meminfo(&si);
141         /* The values below were suggested by Alexey Kuznetsov
142          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
143          * myself.  --SAW
144          */
145         if (si.totalram <= (32768*1024)/PAGE_SIZE)
146                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
147         if (si.totalram <= (16384*1024)/PAGE_SIZE)
148                 inet_peer_threshold >>= 1; /* about 512KB */
149         if (si.totalram <= (8192*1024)/PAGE_SIZE)
150                 inet_peer_threshold >>= 2; /* about 128KB */
151 
152         peer_cachep = kmem_cache_create("inet_peer_cache",
153                         sizeof(struct inet_peer),
154                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
155                         NULL);
156 
157         INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker);
158 }
159 
160 #define rcu_deref_locked(X, BASE)                               \
161         rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
162 
163 /*
164  * Called with local BH disabled and the pool lock held.
165  */
166 #define lookup(_daddr, _stack, _base)                           \
167 ({                                                              \
168         struct inet_peer *u;                                    \
169         struct inet_peer __rcu **v;                             \
170                                                                 \
171         stackptr = _stack;                                      \
172         *stackptr++ = &_base->root;                             \
173         for (u = rcu_deref_locked(_base->root, _base);          \
174              u != peer_avl_empty;) {                            \
175                 int cmp = inetpeer_addr_cmp(_daddr, &u->daddr); \
176                 if (cmp == 0)                                   \
177                         break;                                  \
178                 if (cmp == -1)                                  \
179                         v = &u->avl_left;                       \
180                 else                                            \
181                         v = &u->avl_right;                      \
182                 *stackptr++ = v;                                \
183                 u = rcu_deref_locked(*v, _base);                \
184         }                                                       \
185         u;                                                      \
186 })
187 
188 /*
189  * Called with rcu_read_lock()
190  * Because we hold no lock against a writer, its quite possible we fall
191  * in an endless loop.
192  * But every pointer we follow is guaranteed to be valid thanks to RCU.
193  * We exit from this function if number of links exceeds PEER_MAXDEPTH
194  */
195 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
196                                     struct inet_peer_base *base)
197 {
198         struct inet_peer *u = rcu_dereference(base->root);
199         int count = 0;
200 
201         while (u != peer_avl_empty) {
202                 int cmp = inetpeer_addr_cmp(daddr, &u->daddr);
203                 if (cmp == 0) {
204                         /* Before taking a reference, check if this entry was
205                          * deleted (refcnt=-1)
206                          */
207                         if (!atomic_add_unless(&u->refcnt, 1, -1))
208                                 u = NULL;
209                         return u;
210                 }
211                 if (cmp == -1)
212                         u = rcu_dereference(u->avl_left);
213                 else
214                         u = rcu_dereference(u->avl_right);
215                 if (unlikely(++count == PEER_MAXDEPTH))
216                         break;
217         }
218         return NULL;
219 }
220 
221 /* Called with local BH disabled and the pool lock held. */
222 #define lookup_rightempty(start, base)                          \
223 ({                                                              \
224         struct inet_peer *u;                                    \
225         struct inet_peer __rcu **v;                             \
226         *stackptr++ = &start->avl_left;                         \
227         v = &start->avl_left;                                   \
228         for (u = rcu_deref_locked(*v, base);                    \
229              u->avl_right != peer_avl_empty_rcu;) {             \
230                 v = &u->avl_right;                              \
231                 *stackptr++ = v;                                \
232                 u = rcu_deref_locked(*v, base);                 \
233         }                                                       \
234         u;                                                      \
235 })
236 
237 /* Called with local BH disabled and the pool lock held.
238  * Variable names are the proof of operation correctness.
239  * Look into mm/map_avl.c for more detail description of the ideas.
240  */
241 static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
242                                struct inet_peer __rcu ***stackend,
243                                struct inet_peer_base *base)
244 {
245         struct inet_peer __rcu **nodep;
246         struct inet_peer *node, *l, *r;
247         int lh, rh;
248 
249         while (stackend > stack) {
250                 nodep = *--stackend;
251                 node = rcu_deref_locked(*nodep, base);
252                 l = rcu_deref_locked(node->avl_left, base);
253                 r = rcu_deref_locked(node->avl_right, base);
254                 lh = node_height(l);
255                 rh = node_height(r);
256                 if (lh > rh + 1) { /* l: RH+2 */
257                         struct inet_peer *ll, *lr, *lrl, *lrr;
258                         int lrh;
259                         ll = rcu_deref_locked(l->avl_left, base);
260                         lr = rcu_deref_locked(l->avl_right, base);
261                         lrh = node_height(lr);
262                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
263                                 RCU_INIT_POINTER(node->avl_left, lr);   /* lr: RH or RH+1 */
264                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
265                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
266                                 RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */
267                                 RCU_INIT_POINTER(l->avl_right, node);   /* node: RH+1 or RH+2 */
268                                 l->avl_height = node->avl_height + 1;
269                                 RCU_INIT_POINTER(*nodep, l);
270                         } else { /* ll: RH, lr: RH+1 */
271                                 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
272                                 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
273                                 RCU_INIT_POINTER(node->avl_left, lrr);  /* lrr: RH or RH-1 */
274                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
275                                 node->avl_height = rh + 1; /* node: RH+1 */
276                                 RCU_INIT_POINTER(l->avl_left, ll);      /* ll: RH */
277                                 RCU_INIT_POINTER(l->avl_right, lrl);    /* lrl: RH or RH-1 */
278                                 l->avl_height = rh + 1; /* l: RH+1 */
279                                 RCU_INIT_POINTER(lr->avl_left, l);      /* l: RH+1 */
280                                 RCU_INIT_POINTER(lr->avl_right, node);  /* node: RH+1 */
281                                 lr->avl_height = rh + 2;
282                                 RCU_INIT_POINTER(*nodep, lr);
283                         }
284                 } else if (rh > lh + 1) { /* r: LH+2 */
285                         struct inet_peer *rr, *rl, *rlr, *rll;
286                         int rlh;
287                         rr = rcu_deref_locked(r->avl_right, base);
288                         rl = rcu_deref_locked(r->avl_left, base);
289                         rlh = node_height(rl);
290                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
291                                 RCU_INIT_POINTER(node->avl_right, rl);  /* rl: LH or LH+1 */
292                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
293                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
294                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH+1 */
295                                 RCU_INIT_POINTER(r->avl_left, node);    /* node: LH+1 or LH+2 */
296                                 r->avl_height = node->avl_height + 1;
297                                 RCU_INIT_POINTER(*nodep, r);
298                         } else { /* rr: RH, rl: RH+1 */
299                                 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
300                                 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
301                                 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
302                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
303                                 node->avl_height = lh + 1; /* node: LH+1 */
304                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH */
305                                 RCU_INIT_POINTER(r->avl_left, rlr);     /* rlr: LH or LH-1 */
306                                 r->avl_height = lh + 1; /* r: LH+1 */
307                                 RCU_INIT_POINTER(rl->avl_right, r);     /* r: LH+1 */
308                                 RCU_INIT_POINTER(rl->avl_left, node);   /* node: LH+1 */
309                                 rl->avl_height = lh + 2;
310                                 RCU_INIT_POINTER(*nodep, rl);
311                         }
312                 } else {
313                         node->avl_height = (lh > rh ? lh : rh) + 1;
314                 }
315         }
316 }
317 
318 /* Called with local BH disabled and the pool lock held. */
319 #define link_to_pool(n, base)                                   \
320 do {                                                            \
321         n->avl_height = 1;                                      \
322         n->avl_left = peer_avl_empty_rcu;                       \
323         n->avl_right = peer_avl_empty_rcu;                      \
324         /* lockless readers can catch us now */                 \
325         rcu_assign_pointer(**--stackptr, n);                    \
326         peer_avl_rebalance(stack, stackptr, base);              \
327 } while (0)
328 
329 static void inetpeer_free_rcu(struct rcu_head *head)
330 {
331         kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
332 }
333 
334 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
335                              struct inet_peer __rcu **stack[PEER_MAXDEPTH])
336 {
337         struct inet_peer __rcu ***stackptr, ***delp;
338 
339         if (lookup(&p->daddr, stack, base) != p)
340                 BUG();
341         delp = stackptr - 1; /* *delp[0] == p */
342         if (p->avl_left == peer_avl_empty_rcu) {
343                 *delp[0] = p->avl_right;
344                 --stackptr;
345         } else {
346                 /* look for a node to insert instead of p */
347                 struct inet_peer *t;
348                 t = lookup_rightempty(p, base);
349                 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
350                 **--stackptr = t->avl_left;
351                 /* t is removed, t->daddr > x->daddr for any
352                  * x in p->avl_left subtree.
353                  * Put t in the old place of p. */
354                 RCU_INIT_POINTER(*delp[0], t);
355                 t->avl_left = p->avl_left;
356                 t->avl_right = p->avl_right;
357                 t->avl_height = p->avl_height;
358                 BUG_ON(delp[1] != &p->avl_left);
359                 delp[1] = &t->avl_left; /* was &p->avl_left */
360         }
361         peer_avl_rebalance(stack, stackptr, base);
362         base->total--;
363         call_rcu(&p->rcu, inetpeer_free_rcu);
364 }
365 
366 /* perform garbage collect on all items stacked during a lookup */
367 static int inet_peer_gc(struct inet_peer_base *base,
368                         struct inet_peer __rcu **stack[PEER_MAXDEPTH],
369                         struct inet_peer __rcu ***stackptr)
370 {
371         struct inet_peer *p, *gchead = NULL;
372         __u32 delta, ttl;
373         int cnt = 0;
374 
375         if (base->total >= inet_peer_threshold)
376                 ttl = 0; /* be aggressive */
377         else
378                 ttl = inet_peer_maxttl
379                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
380                                         base->total / inet_peer_threshold * HZ;
381         stackptr--; /* last stack slot is peer_avl_empty */
382         while (stackptr > stack) {
383                 stackptr--;
384                 p = rcu_deref_locked(**stackptr, base);
385                 if (atomic_read(&p->refcnt) == 0) {
386                         smp_rmb();
387                         delta = (__u32)jiffies - p->dtime;
388                         if (delta >= ttl &&
389                             atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
390                                 p->gc_next = gchead;
391                                 gchead = p;
392                         }
393                 }
394         }
395         while ((p = gchead) != NULL) {
396                 gchead = p->gc_next;
397                 cnt++;
398                 unlink_from_pool(p, base, stack);
399         }
400         return cnt;
401 }
402 
403 struct inet_peer *inet_getpeer(struct inet_peer_base *base,
404                                const struct inetpeer_addr *daddr,
405                                int create)
406 {
407         struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
408         struct inet_peer *p;
409         unsigned int sequence;
410         int invalidated, gccnt = 0;
411 
412         /* Attempt a lockless lookup first.
413          * Because of a concurrent writer, we might not find an existing entry.
414          */
415         rcu_read_lock();
416         sequence = read_seqbegin(&base->lock);
417         p = lookup_rcu(daddr, base);
418         invalidated = read_seqretry(&base->lock, sequence);
419         rcu_read_unlock();
420 
421         if (p)
422                 return p;
423 
424         /* If no writer did a change during our lookup, we can return early. */
425         if (!create && !invalidated)
426                 return NULL;
427 
428         /* retry an exact lookup, taking the lock before.
429          * At least, nodes should be hot in our cache.
430          */
431         write_seqlock_bh(&base->lock);
432 relookup:
433         p = lookup(daddr, stack, base);
434         if (p != peer_avl_empty) {
435                 atomic_inc(&p->refcnt);
436                 write_sequnlock_bh(&base->lock);
437                 return p;
438         }
439         if (!gccnt) {
440                 gccnt = inet_peer_gc(base, stack, stackptr);
441                 if (gccnt && create)
442                         goto relookup;
443         }
444         p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
445         if (p) {
446                 p->daddr = *daddr;
447                 atomic_set(&p->refcnt, 1);
448                 atomic_set(&p->rid, 0);
449                 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
450                 p->rate_tokens = 0;
451                 /* 60*HZ is arbitrary, but chosen enough high so that the first
452                  * calculation of tokens is at its maximum.
453                  */
454                 p->rate_last = jiffies - 60*HZ;
455                 INIT_LIST_HEAD(&p->gc_list);
456 
457                 /* Link the node. */
458                 link_to_pool(p, base);
459                 base->total++;
460         }
461         write_sequnlock_bh(&base->lock);
462 
463         return p;
464 }
465 EXPORT_SYMBOL_GPL(inet_getpeer);
466 
467 void inet_putpeer(struct inet_peer *p)
468 {
469         p->dtime = (__u32)jiffies;
470         smp_mb__before_atomic();
471         atomic_dec(&p->refcnt);
472 }
473 EXPORT_SYMBOL_GPL(inet_putpeer);
474 
475 /*
476  *      Check transmit rate limitation for given message.
477  *      The rate information is held in the inet_peer entries now.
478  *      This function is generic and could be used for other purposes
479  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
480  *
481  *      Note that the same inet_peer fields are modified by functions in
482  *      route.c too, but these work for packet destinations while xrlim_allow
483  *      works for icmp destinations. This means the rate limiting information
484  *      for one "ip object" is shared - and these ICMPs are twice limited:
485  *      by source and by destination.
486  *
487  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
488  *                        SHOULD allow setting of rate limits
489  *
490  *      Shared between ICMPv4 and ICMPv6.
491  */
492 #define XRLIM_BURST_FACTOR 6
493 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
494 {
495         unsigned long now, token;
496         bool rc = false;
497 
498         if (!peer)
499                 return true;
500 
501         token = peer->rate_tokens;
502         now = jiffies;
503         token += now - peer->rate_last;
504         peer->rate_last = now;
505         if (token > XRLIM_BURST_FACTOR * timeout)
506                 token = XRLIM_BURST_FACTOR * timeout;
507         if (token >= timeout) {
508                 token -= timeout;
509                 rc = true;
510         }
511         peer->rate_tokens = token;
512         return rc;
513 }
514 EXPORT_SYMBOL(inet_peer_xrlim_allow);
515 
516 static void inetpeer_inval_rcu(struct rcu_head *head)
517 {
518         struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
519 
520         spin_lock_bh(&gc_lock);
521         list_add_tail(&p->gc_list, &gc_list);
522         spin_unlock_bh(&gc_lock);
523 
524         schedule_delayed_work(&gc_work, gc_delay);
525 }
526 
527 void inetpeer_invalidate_tree(struct inet_peer_base *base)
528 {
529         struct inet_peer *root;
530 
531         write_seqlock_bh(&base->lock);
532 
533         root = rcu_deref_locked(base->root, base);
534         if (root != peer_avl_empty) {
535                 base->root = peer_avl_empty_rcu;
536                 base->total = 0;
537                 call_rcu(&root->gc_rcu, inetpeer_inval_rcu);
538         }
539 
540         write_sequnlock_bh(&base->lock);
541 }
542 EXPORT_SYMBOL(inetpeer_invalidate_tree);
543 

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