/* * 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 */ #include #include #include #include #include #include #include #include #include #include #include #include #include /* * 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 lock held. * 2. Nodes may disappear from the tree only with the pool 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 * daddr: unchangeable * ip_id_count: atomic value (no lock needed) */ static struct kmem_cache *peer_cachep __read_mostly; #define node_height(x) x->avl_height #define peer_avl_empty ((struct inet_peer *)&peer_fake_node) #define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node) static const struct inet_peer peer_fake_node = { .avl_left = peer_avl_empty_rcu, .avl_right = peer_avl_empty_rcu, .avl_height = 0 }; static struct inet_peer_base { struct inet_peer __rcu *root; spinlock_t lock; int total; } v4_peers = { .root = peer_avl_empty_rcu, .lock = __SPIN_LOCK_UNLOCKED(v4_peers.lock), .total = 0, }; #define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ /* 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 struct { struct list_head list; spinlock_t lock; } unused_peers = { .list = LIST_HEAD_INIT(unused_peers.list), .lock = __SPIN_LOCK_UNLOCKED(unused_peers.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 * . 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) { if (!list_empty(&p->unused)) { spin_lock_bh(&unused_peers.lock); list_del_init(&p->unused); spin_unlock_bh(&unused_peers.lock); } } /* * Called with local BH disabled and the pool lock held. */ #define lookup(_daddr, _stack, _base) \ ({ \ struct inet_peer *u; \ struct inet_peer __rcu **v; \ \ stackptr = _stack; \ *stackptr++ = &_base->root; \ for (u = rcu_dereference_protected(_base->root, \ lockdep_is_held(&_base->lock)); \ u != peer_avl_empty; ) { \ if (_daddr == u->daddr.a4) \ break; \ if ((__force __u32)_daddr < (__force __u32)u->daddr.a4) \ v = &u->avl_left; \ else \ v = &u->avl_right; \ *stackptr++ = v; \ u = rcu_dereference_protected(*v, \ lockdep_is_held(&_base->lock)); \ } \ u; \ }) /* * Called with rcu_read_lock_bh() * Because we hold no lock against a writer, its quite possible we fall * in an endless loop. * But every pointer we follow is guaranteed to be valid thanks to RCU. * We exit from this function if number of links exceeds PEER_MAXDEPTH */ static struct inet_peer *lookup_rcu_bh(__be32 daddr, struct inet_peer_base *base) { struct inet_peer *u = rcu_dereference_bh(base->root); int count = 0; while (u != peer_avl_empty) { if (daddr == u->daddr.a4) { /* Before taking a reference, check if this entry was * deleted, unlink_from_pool() sets refcnt=-1 to make * distinction between an unused entry (refcnt=0) and * a freed one. */ if (unlikely(!atomic_add_unless(&u->refcnt, 1, -1))) u = NULL; return u; } if ((__force __u32)daddr < (__force __u32)u->daddr.a4) u = rcu_dereference_bh(u->avl_left); else u = rcu_dereference_bh(u->avl_right); if (unlikely(++count == PEER_MAXDEPTH)) break; } return NULL; } /* Called with local BH disabled and the pool lock held. */ #define lookup_rightempty(start, base) \ ({ \ struct inet_peer *u; \ struct inet_peer __rcu **v; \ *stackptr++ = &start->avl_left; \ v = &start->avl_left; \ for (u = rcu_dereference_protected(*v, \ lockdep_is_held(&base->lock)); \ u->avl_right != peer_avl_empty_rcu; ) { \ v = &u->avl_right; \ *stackptr++ = v; \ u = rcu_dereference_protected(*v, \ lockdep_is_held(&base->lock)); \ } \ u; \ }) /* Called with local BH disabled and the pool 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 __rcu **stack[], struct inet_peer __rcu ***stackend, struct inet_peer_base *base) { struct inet_peer __rcu **nodep; struct inet_peer *node, *l, *r; int lh, rh; while (stackend > stack) { nodep = *--stackend; node = rcu_dereference_protected(*nodep, lockdep_is_held(&base->lock)); l = rcu_dereference_protected(node->avl_left, lockdep_is_held(&base->lock)); r = rcu_dereference_protected(node->avl_right, lockdep_is_held(&base->lock)); 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 = rcu_dereference_protected(l->avl_left, lockdep_is_held(&base->lock)); lr = rcu_dereference_protected(l->avl_right, lockdep_is_held(&base->lock)); lrh = node_height(lr); if (lrh <= node_height(ll)) { /* ll: RH+1 */ RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */ RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ node->avl_height = lrh + 1; /* RH+1 or RH+2 */ RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */ RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */ l->avl_height = node->avl_height + 1; RCU_INIT_POINTER(*nodep, l); } else { /* ll: RH, lr: RH+1 */ lrl = rcu_dereference_protected(lr->avl_left, lockdep_is_held(&base->lock)); /* lrl: RH or RH-1 */ lrr = rcu_dereference_protected(lr->avl_right, lockdep_is_held(&base->lock)); /* lrr: RH or RH-1 */ RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */ RCU_INIT_POINTER(node->avl_right, r); /* r: RH */ node->avl_height = rh + 1; /* node: RH+1 */ RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */ RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */ l->avl_height = rh + 1; /* l: RH+1 */ RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */ RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */ lr->avl_height = rh + 2; RCU_INIT_POINTER(*nodep, lr); } } else if (rh > lh + 1) { /* r: LH+2 */ struct inet_peer *rr, *rl, *rlr, *rll; int rlh; rr = rcu_dereference_protected(r->avl_right, lockdep_is_held(&base->lock)); rl = rcu_dereference_protected(r->avl_left, lockdep_is_held(&base->lock)); rlh = node_height(rl); if (rlh <= node_height(rr)) { /* rr: LH+1 */ RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */ RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ node->avl_height = rlh + 1; /* LH+1 or LH+2 */ RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */ RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */ r->avl_height = node->avl_height + 1; RCU_INIT_POINTER(*nodep, r); } else { /* rr: RH, rl: RH+1 */ rlr = rcu_dereference_protected(rl->avl_right, lockdep_is_held(&base->lock)); /* rlr: LH or LH-1 */ rll = rcu_dereference_protected(rl->avl_left, lockdep_is_held(&base->lock)); /* rll: LH or LH-1 */ RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */ RCU_INIT_POINTER(node->avl_left, l); /* l: LH */ node->avl_height = lh + 1; /* node: LH+1 */ RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */ RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */ r->avl_height = lh + 1; /* r: LH+1 */ RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */ RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */ rl->avl_height = lh + 2; RCU_INIT_POINTER(*nodep, rl); } } else { node->avl_height = (lh > rh ? lh : rh) + 1; } } } /* Called with local BH disabled and the pool lock held. */ #define link_to_pool(n, base) \ do { \ n->avl_height = 1; \ n->avl_left = peer_avl_empty_rcu; \ n->avl_right = peer_avl_empty_rcu; \ /* lockless readers can catch us now */ \ rcu_assign_pointer(**--stackptr, n); \ peer_avl_rebalance(stack, stackptr, base); \ } while (0) static void inetpeer_free_rcu(struct rcu_head *head) { kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); } /* May be called with local BH enabled. */ static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base) { int do_free; do_free = 0; spin_lock_bh(&base->lock); /* Check the reference counter. It was artificially incremented by 1 * in cleanup() function to prevent sudden disappearing. If we can * atomically (because of lockless readers) take this last reference, * it's safe to remove the node and free it later. * We use refcnt=-1 to alert lockless readers this entry is deleted. */ if (atomic_cmpxchg(&p->refcnt, 1, -1) == 1) { struct inet_peer __rcu **stack[PEER_MAXDEPTH]; struct inet_peer __rcu ***stackptr, ***delp; if (lookup(p->daddr.a4, stack, base) != p) BUG(); delp = stackptr - 1; /* *delp[0] == p */ if (p->avl_left == peer_avl_empty_rcu) { *delp[0] = p->avl_right; --stackptr; } else { /* look for a node to insert instead of p */ struct inet_peer *t; t = lookup_rightempty(p, base); BUG_ON(rcu_dereference_protected(*stackptr[-1], lockdep_is_held(&base->lock)) != t); **--stackptr = t->avl_left; /* t is removed, t->daddr > x->daddr for any * x in p->avl_left subtree. * Put t in the old place of p. */ RCU_INIT_POINTER(*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, base); base->total--; do_free = 1; } spin_unlock_bh(&base->lock); if (do_free) call_rcu_bh(&p->rcu, inetpeer_free_rcu); 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); } static struct inet_peer_base *peer_to_base(struct inet_peer *p) { return &v4_peers; } /* 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(&unused_peers.lock); if (!list_empty(&unused_peers.list)) { __u32 delta; p = list_first_entry(&unused_peers.list, struct inet_peer, unused); delta = (__u32)jiffies - p->dtime; if (delta < ttl) { /* Do not prune fresh entries. */ spin_unlock_bh(&unused_peers.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(&unused_peers.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, peer_to_base(p)); return 0; } static struct inet_peer_base *family_to_base(int family) { return &v4_peers; } /* Called with or without local BH being disabled. */ struct inet_peer *inet_getpeer(inet_peer_address_t *daddr, int create) { struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr; struct inet_peer_base *base = family_to_base(AF_INET); struct inet_peer *p; /* Look up for the address quickly, lockless. * Because of a concurrent writer, we might not find an existing entry. */ rcu_read_lock_bh(); p = lookup_rcu_bh(daddr->a4, base); rcu_read_unlock_bh(); if (p) { /* The existing node has been found. * Remove the entry from unused list if it was there. */ unlink_from_unused(p); return p; } /* retry an exact lookup, taking the lock before. * At least, nodes should be hot in our cache. */ spin_lock_bh(&base->lock); p = lookup(daddr->a4, stack, base); if (p != peer_avl_empty) { atomic_inc(&p->refcnt); spin_unlock_bh(&base->lock); /* Remove the entry from unused list if it was there. */ unlink_from_unused(p); return p; } p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL; if (p) { p->daddr = *daddr; atomic_set(&p->refcnt, 1); atomic_set(&p->rid, 0); atomic_set(&p->ip_id_count, secure_ip_id(daddr->a4)); p->tcp_ts_stamp = 0; INIT_LIST_HEAD(&p->unused); /* Link the node. */ link_to_pool(p, base); base->total++; } spin_unlock_bh(&base->lock); if (base->total >= inet_peer_threshold) /* Remove one less-recently-used entry. */ cleanup_once(0); return p; } static int compute_total(void) { return v4_peers.total; } /* Called with local BH disabled. */ static void peer_check_expire(unsigned long dummy) { unsigned long now = jiffies; int ttl, total; total = compute_total(); if (total >= inet_peer_threshold) ttl = inet_peer_minttl; else ttl = inet_peer_maxttl - (inet_peer_maxttl - inet_peer_minttl) / HZ * 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). */ total = compute_total(); if (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 * total / inet_peer_threshold * HZ; add_timer(&peer_periodic_timer); } void inet_putpeer(struct inet_peer *p) { local_bh_disable(); if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) { list_add_tail(&p->unused, &unused_peers.list); p->dtime = (__u32)jiffies; spin_unlock(&unused_peers.lock); } local_bh_enable(); }