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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->flush_seq = ~0U;
 76         bp->total = 0;
 77 }
 78 EXPORT_SYMBOL_GPL(inet_peer_base_init);
 79 
 80 static atomic_t v4_seq = ATOMIC_INIT(0);
 81 static atomic_t v6_seq = ATOMIC_INIT(0);
 82 
 83 static atomic_t *inetpeer_seq_ptr(int family)
 84 {
 85         return (family == AF_INET ? &v4_seq : &v6_seq);
 86 }
 87 
 88 static inline void flush_check(struct inet_peer_base *base, int family)
 89 {
 90         atomic_t *fp = inetpeer_seq_ptr(family);
 91 
 92         if (unlikely(base->flush_seq != atomic_read(fp))) {
 93                 inetpeer_invalidate_tree(base);
 94                 base->flush_seq = atomic_read(fp);
 95         }
 96 }
 97 
 98 void inetpeer_invalidate_family(int family)
 99 {
100         atomic_t *fp = inetpeer_seq_ptr(family);
101 
102         atomic_inc(fp);
103 }
104 
105 #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
106 
107 /* Exported for sysctl_net_ipv4.  */
108 int inet_peer_threshold __read_mostly = 65536 + 128;    /* start to throw entries more
109                                          * aggressively at this stage */
110 int inet_peer_minttl __read_mostly = 120 * HZ;  /* TTL under high load: 120 sec */
111 int inet_peer_maxttl __read_mostly = 10 * 60 * HZ;      /* usual time to live: 10 min */
112 
113 static void inetpeer_gc_worker(struct work_struct *work)
114 {
115         struct inet_peer *p, *n, *c;
116         LIST_HEAD(list);
117 
118         spin_lock_bh(&gc_lock);
119         list_replace_init(&gc_list, &list);
120         spin_unlock_bh(&gc_lock);
121 
122         if (list_empty(&list))
123                 return;
124 
125         list_for_each_entry_safe(p, n, &list, gc_list) {
126 
127                 if (need_resched())
128                         cond_resched();
129 
130                 c = rcu_dereference_protected(p->avl_left, 1);
131                 if (c != peer_avl_empty) {
132                         list_add_tail(&c->gc_list, &list);
133                         p->avl_left = peer_avl_empty_rcu;
134                 }
135 
136                 c = rcu_dereference_protected(p->avl_right, 1);
137                 if (c != peer_avl_empty) {
138                         list_add_tail(&c->gc_list, &list);
139                         p->avl_right = peer_avl_empty_rcu;
140                 }
141 
142                 n = list_entry(p->gc_list.next, struct inet_peer, gc_list);
143 
144                 if (!atomic_read(&p->refcnt)) {
145                         list_del(&p->gc_list);
146                         kmem_cache_free(peer_cachep, p);
147                 }
148         }
149 
150         if (list_empty(&list))
151                 return;
152 
153         spin_lock_bh(&gc_lock);
154         list_splice(&list, &gc_list);
155         spin_unlock_bh(&gc_lock);
156 
157         schedule_delayed_work(&gc_work, gc_delay);
158 }
159 
160 /* Called from ip_output.c:ip_init  */
161 void __init inet_initpeers(void)
162 {
163         struct sysinfo si;
164 
165         /* Use the straight interface to information about memory. */
166         si_meminfo(&si);
167         /* The values below were suggested by Alexey Kuznetsov
168          * <kuznet@ms2.inr.ac.ru>.  I don't have any opinion about the values
169          * myself.  --SAW
170          */
171         if (si.totalram <= (32768*1024)/PAGE_SIZE)
172                 inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
173         if (si.totalram <= (16384*1024)/PAGE_SIZE)
174                 inet_peer_threshold >>= 1; /* about 512KB */
175         if (si.totalram <= (8192*1024)/PAGE_SIZE)
176                 inet_peer_threshold >>= 2; /* about 128KB */
177 
178         peer_cachep = kmem_cache_create("inet_peer_cache",
179                         sizeof(struct inet_peer),
180                         0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
181                         NULL);
182 
183         INIT_DEFERRABLE_WORK(&gc_work, inetpeer_gc_worker);
184 }
185 
186 static int addr_compare(const struct inetpeer_addr *a,
187                         const struct inetpeer_addr *b)
188 {
189         int i, n = (a->family == AF_INET ? 1 : 4);
190 
191         for (i = 0; i < n; i++) {
192                 if (a->addr.a6[i] == b->addr.a6[i])
193                         continue;
194                 if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i])
195                         return -1;
196                 return 1;
197         }
198 
199         return 0;
200 }
201 
202 #define rcu_deref_locked(X, BASE)                               \
203         rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
204 
205 /*
206  * Called with local BH disabled and the pool lock held.
207  */
208 #define lookup(_daddr, _stack, _base)                           \
209 ({                                                              \
210         struct inet_peer *u;                                    \
211         struct inet_peer __rcu **v;                             \
212                                                                 \
213         stackptr = _stack;                                      \
214         *stackptr++ = &_base->root;                             \
215         for (u = rcu_deref_locked(_base->root, _base);          \
216              u != peer_avl_empty; ) {                           \
217                 int cmp = addr_compare(_daddr, &u->daddr);      \
218                 if (cmp == 0)                                   \
219                         break;                                  \
220                 if (cmp == -1)                                  \
221                         v = &u->avl_left;                       \
222                 else                                            \
223                         v = &u->avl_right;                      \
224                 *stackptr++ = v;                                \
225                 u = rcu_deref_locked(*v, _base);                \
226         }                                                       \
227         u;                                                      \
228 })
229 
230 /*
231  * Called with rcu_read_lock()
232  * Because we hold no lock against a writer, its quite possible we fall
233  * in an endless loop.
234  * But every pointer we follow is guaranteed to be valid thanks to RCU.
235  * We exit from this function if number of links exceeds PEER_MAXDEPTH
236  */
237 static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
238                                     struct inet_peer_base *base)
239 {
240         struct inet_peer *u = rcu_dereference(base->root);
241         int count = 0;
242 
243         while (u != peer_avl_empty) {
244                 int cmp = addr_compare(daddr, &u->daddr);
245                 if (cmp == 0) {
246                         /* Before taking a reference, check if this entry was
247                          * deleted (refcnt=-1)
248                          */
249                         if (!atomic_add_unless(&u->refcnt, 1, -1))
250                                 u = NULL;
251                         return u;
252                 }
253                 if (cmp == -1)
254                         u = rcu_dereference(u->avl_left);
255                 else
256                         u = rcu_dereference(u->avl_right);
257                 if (unlikely(++count == PEER_MAXDEPTH))
258                         break;
259         }
260         return NULL;
261 }
262 
263 /* Called with local BH disabled and the pool lock held. */
264 #define lookup_rightempty(start, base)                          \
265 ({                                                              \
266         struct inet_peer *u;                                    \
267         struct inet_peer __rcu **v;                             \
268         *stackptr++ = &start->avl_left;                         \
269         v = &start->avl_left;                                   \
270         for (u = rcu_deref_locked(*v, base);                    \
271              u->avl_right != peer_avl_empty_rcu; ) {            \
272                 v = &u->avl_right;                              \
273                 *stackptr++ = v;                                \
274                 u = rcu_deref_locked(*v, base);                 \
275         }                                                       \
276         u;                                                      \
277 })
278 
279 /* Called with local BH disabled and the pool lock held.
280  * Variable names are the proof of operation correctness.
281  * Look into mm/map_avl.c for more detail description of the ideas.
282  */
283 static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
284                                struct inet_peer __rcu ***stackend,
285                                struct inet_peer_base *base)
286 {
287         struct inet_peer __rcu **nodep;
288         struct inet_peer *node, *l, *r;
289         int lh, rh;
290 
291         while (stackend > stack) {
292                 nodep = *--stackend;
293                 node = rcu_deref_locked(*nodep, base);
294                 l = rcu_deref_locked(node->avl_left, base);
295                 r = rcu_deref_locked(node->avl_right, base);
296                 lh = node_height(l);
297                 rh = node_height(r);
298                 if (lh > rh + 1) { /* l: RH+2 */
299                         struct inet_peer *ll, *lr, *lrl, *lrr;
300                         int lrh;
301                         ll = rcu_deref_locked(l->avl_left, base);
302                         lr = rcu_deref_locked(l->avl_right, base);
303                         lrh = node_height(lr);
304                         if (lrh <= node_height(ll)) {   /* ll: RH+1 */
305                                 RCU_INIT_POINTER(node->avl_left, lr);   /* lr: RH or RH+1 */
306                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
307                                 node->avl_height = lrh + 1; /* RH+1 or RH+2 */
308                                 RCU_INIT_POINTER(l->avl_left, ll);       /* ll: RH+1 */
309                                 RCU_INIT_POINTER(l->avl_right, node);   /* node: RH+1 or RH+2 */
310                                 l->avl_height = node->avl_height + 1;
311                                 RCU_INIT_POINTER(*nodep, l);
312                         } else { /* ll: RH, lr: RH+1 */
313                                 lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
314                                 lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
315                                 RCU_INIT_POINTER(node->avl_left, lrr);  /* lrr: RH or RH-1 */
316                                 RCU_INIT_POINTER(node->avl_right, r);   /* r: RH */
317                                 node->avl_height = rh + 1; /* node: RH+1 */
318                                 RCU_INIT_POINTER(l->avl_left, ll);      /* ll: RH */
319                                 RCU_INIT_POINTER(l->avl_right, lrl);    /* lrl: RH or RH-1 */
320                                 l->avl_height = rh + 1; /* l: RH+1 */
321                                 RCU_INIT_POINTER(lr->avl_left, l);      /* l: RH+1 */
322                                 RCU_INIT_POINTER(lr->avl_right, node);  /* node: RH+1 */
323                                 lr->avl_height = rh + 2;
324                                 RCU_INIT_POINTER(*nodep, lr);
325                         }
326                 } else if (rh > lh + 1) { /* r: LH+2 */
327                         struct inet_peer *rr, *rl, *rlr, *rll;
328                         int rlh;
329                         rr = rcu_deref_locked(r->avl_right, base);
330                         rl = rcu_deref_locked(r->avl_left, base);
331                         rlh = node_height(rl);
332                         if (rlh <= node_height(rr)) {   /* rr: LH+1 */
333                                 RCU_INIT_POINTER(node->avl_right, rl);  /* rl: LH or LH+1 */
334                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
335                                 node->avl_height = rlh + 1; /* LH+1 or LH+2 */
336                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH+1 */
337                                 RCU_INIT_POINTER(r->avl_left, node);    /* node: LH+1 or LH+2 */
338                                 r->avl_height = node->avl_height + 1;
339                                 RCU_INIT_POINTER(*nodep, r);
340                         } else { /* rr: RH, rl: RH+1 */
341                                 rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
342                                 rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
343                                 RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
344                                 RCU_INIT_POINTER(node->avl_left, l);    /* l: LH */
345                                 node->avl_height = lh + 1; /* node: LH+1 */
346                                 RCU_INIT_POINTER(r->avl_right, rr);     /* rr: LH */
347                                 RCU_INIT_POINTER(r->avl_left, rlr);     /* rlr: LH or LH-1 */
348                                 r->avl_height = lh + 1; /* r: LH+1 */
349                                 RCU_INIT_POINTER(rl->avl_right, r);     /* r: LH+1 */
350                                 RCU_INIT_POINTER(rl->avl_left, node);   /* node: LH+1 */
351                                 rl->avl_height = lh + 2;
352                                 RCU_INIT_POINTER(*nodep, rl);
353                         }
354                 } else {
355                         node->avl_height = (lh > rh ? lh : rh) + 1;
356                 }
357         }
358 }
359 
360 /* Called with local BH disabled and the pool lock held. */
361 #define link_to_pool(n, base)                                   \
362 do {                                                            \
363         n->avl_height = 1;                                      \
364         n->avl_left = peer_avl_empty_rcu;                       \
365         n->avl_right = peer_avl_empty_rcu;                      \
366         /* lockless readers can catch us now */                 \
367         rcu_assign_pointer(**--stackptr, n);                    \
368         peer_avl_rebalance(stack, stackptr, base);              \
369 } while (0)
370 
371 static void inetpeer_free_rcu(struct rcu_head *head)
372 {
373         kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
374 }
375 
376 static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
377                              struct inet_peer __rcu **stack[PEER_MAXDEPTH])
378 {
379         struct inet_peer __rcu ***stackptr, ***delp;
380 
381         if (lookup(&p->daddr, stack, base) != p)
382                 BUG();
383         delp = stackptr - 1; /* *delp[0] == p */
384         if (p->avl_left == peer_avl_empty_rcu) {
385                 *delp[0] = p->avl_right;
386                 --stackptr;
387         } else {
388                 /* look for a node to insert instead of p */
389                 struct inet_peer *t;
390                 t = lookup_rightempty(p, base);
391                 BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
392                 **--stackptr = t->avl_left;
393                 /* t is removed, t->daddr > x->daddr for any
394                  * x in p->avl_left subtree.
395                  * Put t in the old place of p. */
396                 RCU_INIT_POINTER(*delp[0], t);
397                 t->avl_left = p->avl_left;
398                 t->avl_right = p->avl_right;
399                 t->avl_height = p->avl_height;
400                 BUG_ON(delp[1] != &p->avl_left);
401                 delp[1] = &t->avl_left; /* was &p->avl_left */
402         }
403         peer_avl_rebalance(stack, stackptr, base);
404         base->total--;
405         call_rcu(&p->rcu, inetpeer_free_rcu);
406 }
407 
408 /* perform garbage collect on all items stacked during a lookup */
409 static int inet_peer_gc(struct inet_peer_base *base,
410                         struct inet_peer __rcu **stack[PEER_MAXDEPTH],
411                         struct inet_peer __rcu ***stackptr)
412 {
413         struct inet_peer *p, *gchead = NULL;
414         __u32 delta, ttl;
415         int cnt = 0;
416 
417         if (base->total >= inet_peer_threshold)
418                 ttl = 0; /* be aggressive */
419         else
420                 ttl = inet_peer_maxttl
421                                 - (inet_peer_maxttl - inet_peer_minttl) / HZ *
422                                         base->total / inet_peer_threshold * HZ;
423         stackptr--; /* last stack slot is peer_avl_empty */
424         while (stackptr > stack) {
425                 stackptr--;
426                 p = rcu_deref_locked(**stackptr, base);
427                 if (atomic_read(&p->refcnt) == 0) {
428                         smp_rmb();
429                         delta = (__u32)jiffies - p->dtime;
430                         if (delta >= ttl &&
431                             atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
432                                 p->gc_next = gchead;
433                                 gchead = p;
434                         }
435                 }
436         }
437         while ((p = gchead) != NULL) {
438                 gchead = p->gc_next;
439                 cnt++;
440                 unlink_from_pool(p, base, stack);
441         }
442         return cnt;
443 }
444 
445 struct inet_peer *inet_getpeer(struct inet_peer_base *base,
446                                const struct inetpeer_addr *daddr,
447                                int create)
448 {
449         struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
450         struct inet_peer *p;
451         unsigned int sequence;
452         int invalidated, gccnt = 0;
453 
454         flush_check(base, daddr->family);
455 
456         /* Attempt a lockless lookup first.
457          * Because of a concurrent writer, we might not find an existing entry.
458          */
459         rcu_read_lock();
460         sequence = read_seqbegin(&base->lock);
461         p = lookup_rcu(daddr, base);
462         invalidated = read_seqretry(&base->lock, sequence);
463         rcu_read_unlock();
464 
465         if (p)
466                 return p;
467 
468         /* If no writer did a change during our lookup, we can return early. */
469         if (!create && !invalidated)
470                 return NULL;
471 
472         /* retry an exact lookup, taking the lock before.
473          * At least, nodes should be hot in our cache.
474          */
475         write_seqlock_bh(&base->lock);
476 relookup:
477         p = lookup(daddr, stack, base);
478         if (p != peer_avl_empty) {
479                 atomic_inc(&p->refcnt);
480                 write_sequnlock_bh(&base->lock);
481                 return p;
482         }
483         if (!gccnt) {
484                 gccnt = inet_peer_gc(base, stack, stackptr);
485                 if (gccnt && create)
486                         goto relookup;
487         }
488         p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
489         if (p) {
490                 p->daddr = *daddr;
491                 atomic_set(&p->refcnt, 1);
492                 atomic_set(&p->rid, 0);
493                 p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
494                 p->rate_tokens = 0;
495                 /* 60*HZ is arbitrary, but chosen enough high so that the first
496                  * calculation of tokens is at its maximum.
497                  */
498                 p->rate_last = jiffies - 60*HZ;
499                 INIT_LIST_HEAD(&p->gc_list);
500 
501                 /* Link the node. */
502                 link_to_pool(p, base);
503                 base->total++;
504         }
505         write_sequnlock_bh(&base->lock);
506 
507         return p;
508 }
509 EXPORT_SYMBOL_GPL(inet_getpeer);
510 
511 void inet_putpeer(struct inet_peer *p)
512 {
513         p->dtime = (__u32)jiffies;
514         smp_mb__before_atomic_dec();
515         atomic_dec(&p->refcnt);
516 }
517 EXPORT_SYMBOL_GPL(inet_putpeer);
518 
519 /*
520  *      Check transmit rate limitation for given message.
521  *      The rate information is held in the inet_peer entries now.
522  *      This function is generic and could be used for other purposes
523  *      too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
524  *
525  *      Note that the same inet_peer fields are modified by functions in
526  *      route.c too, but these work for packet destinations while xrlim_allow
527  *      works for icmp destinations. This means the rate limiting information
528  *      for one "ip object" is shared - and these ICMPs are twice limited:
529  *      by source and by destination.
530  *
531  *      RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
532  *                        SHOULD allow setting of rate limits
533  *
534  *      Shared between ICMPv4 and ICMPv6.
535  */
536 #define XRLIM_BURST_FACTOR 6
537 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
538 {
539         unsigned long now, token;
540         bool rc = false;
541 
542         if (!peer)
543                 return true;
544 
545         token = peer->rate_tokens;
546         now = jiffies;
547         token += now - peer->rate_last;
548         peer->rate_last = now;
549         if (token > XRLIM_BURST_FACTOR * timeout)
550                 token = XRLIM_BURST_FACTOR * timeout;
551         if (token >= timeout) {
552                 token -= timeout;
553                 rc = true;
554         }
555         peer->rate_tokens = token;
556         return rc;
557 }
558 EXPORT_SYMBOL(inet_peer_xrlim_allow);
559 
560 static void inetpeer_inval_rcu(struct rcu_head *head)
561 {
562         struct inet_peer *p = container_of(head, struct inet_peer, gc_rcu);
563 
564         spin_lock_bh(&gc_lock);
565         list_add_tail(&p->gc_list, &gc_list);
566         spin_unlock_bh(&gc_lock);
567 
568         schedule_delayed_work(&gc_work, gc_delay);
569 }
570 
571 void inetpeer_invalidate_tree(struct inet_peer_base *base)
572 {
573         struct inet_peer *root;
574 
575         write_seqlock_bh(&base->lock);
576 
577         root = rcu_deref_locked(base->root, base);
578         if (root != peer_avl_empty) {
579                 base->root = peer_avl_empty_rcu;
580                 base->total = 0;
581                 call_rcu(&root->gc_rcu, inetpeer_inval_rcu);
582         }
583 
584         write_sequnlock_bh(&base->lock);
585 }
586 EXPORT_SYMBOL(inetpeer_invalidate_tree);
587 

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