/* * 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 #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. * * 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 RB 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. Global variable peer_total is modified under the pool lock. * 4. struct inet_peer fields modification: * rb_node: pool lock * refcnt: atomically against modifications on other CPU; * usually under some other lock to prevent node disappearing * daddr: unchangeable */ static struct kmem_cache *peer_cachep __ro_after_init; void inet_peer_base_init(struct inet_peer_base *bp) { bp->rb_root = RB_ROOT; seqlock_init(&bp->lock); bp->total = 0; } EXPORT_SYMBOL_GPL(inet_peer_base_init); #define PEER_MAX_GC 32 /* Exported for sysctl_net_ipv4. */ int inet_peer_threshold __read_mostly; /* 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 */ /* Called from ip_output.c:ip_init */ void __init inet_initpeers(void) { u64 nr_entries; /* 1% of physical memory */ nr_entries = div64_ul((u64)totalram_pages() << PAGE_SHIFT, 100 * L1_CACHE_ALIGN(sizeof(struct inet_peer))); inet_peer_threshold = clamp_val(nr_entries, 4096, 65536 + 128); peer_cachep = kmem_cache_create("inet_peer_cache", sizeof(struct inet_peer), 0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL); } /* Called with rcu_read_lock() or base->lock held */ static struct inet_peer *lookup(const struct inetpeer_addr *daddr, struct inet_peer_base *base, unsigned int seq, struct inet_peer *gc_stack[], unsigned int *gc_cnt, struct rb_node **parent_p, struct rb_node ***pp_p) { struct rb_node **pp, *parent, *next; struct inet_peer *p; pp = &base->rb_root.rb_node; parent = NULL; while (1) { int cmp; next = rcu_dereference_raw(*pp); if (!next) break; parent = next; p = rb_entry(parent, struct inet_peer, rb_node); cmp = inetpeer_addr_cmp(daddr, &p->daddr); if (cmp == 0) { if (!refcount_inc_not_zero(&p->refcnt)) break; return p; } if (gc_stack) { if (*gc_cnt < PEER_MAX_GC) gc_stack[(*gc_cnt)++] = p; } else if (unlikely(read_seqretry(&base->lock, seq))) { break; } if (cmp == -1) pp = &next->rb_left; else pp = &next->rb_right; } *parent_p = parent; *pp_p = pp; return NULL; } static void inetpeer_free_rcu(struct rcu_head *head) { kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu)); } /* perform garbage collect on all items stacked during a lookup */ static void inet_peer_gc(struct inet_peer_base *base, struct inet_peer *gc_stack[], unsigned int gc_cnt) { int peer_threshold, peer_maxttl, peer_minttl; struct inet_peer *p; __u32 delta, ttl; int i; peer_threshold = READ_ONCE(inet_peer_threshold); peer_maxttl = READ_ONCE(inet_peer_maxttl); peer_minttl = READ_ONCE(inet_peer_minttl); if (base->total >= peer_threshold) ttl = 0; /* be aggressive */ else ttl = peer_maxttl - (peer_maxttl - peer_minttl) / HZ * base->total / peer_threshold * HZ; for (i = 0; i < gc_cnt; i++) { p = gc_stack[i]; /* The READ_ONCE() pairs with the WRITE_ONCE() * in inet_putpeer() */ delta = (__u32)jiffies - READ_ONCE(p->dtime); if (delta < ttl || !refcount_dec_if_one(&p->refcnt)) gc_stack[i] = NULL; } for (i = 0; i < gc_cnt; i++) { p = gc_stack[i]; if (p) { rb_erase(&p->rb_node, &base->rb_root); base->total--; call_rcu(&p->rcu, inetpeer_free_rcu); } } } struct inet_peer *inet_getpeer(struct inet_peer_base *base, const struct inetpeer_addr *daddr, int create) { struct inet_peer *p, *gc_stack[PEER_MAX_GC]; struct rb_node **pp, *parent; unsigned int gc_cnt, seq; int invalidated; /* Attempt a lockless lookup first. * Because of a concurrent writer, we might not find an existing entry. */ rcu_read_lock(); seq = read_seqbegin(&base->lock); p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp); invalidated = read_seqretry(&base->lock, seq); rcu_read_unlock(); if (p) return p; /* If no writer did a change during our lookup, we can return early. */ if (!create && !invalidated) return NULL; /* retry an exact lookup, taking the lock before. * At least, nodes should be hot in our cache. */ parent = NULL; write_seqlock_bh(&base->lock); gc_cnt = 0; p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp); if (!p && create) { p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); if (p) { p->daddr = *daddr; p->dtime = (__u32)jiffies; refcount_set(&p->refcnt, 2); atomic_set(&p->rid, 0); p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW; p->rate_tokens = 0; p->n_redirects = 0; /* 60*HZ is arbitrary, but chosen enough high so that the first * calculation of tokens is at its maximum. */ p->rate_last = jiffies - 60*HZ; rb_link_node(&p->rb_node, parent, pp); rb_insert_color(&p->rb_node, &base->rb_root); base->total++; } } if (gc_cnt) inet_peer_gc(base, gc_stack, gc_cnt); write_sequnlock_bh(&base->lock); return p; } EXPORT_SYMBOL_GPL(inet_getpeer); void inet_putpeer(struct inet_peer *p) { /* The WRITE_ONCE() pairs with itself (we run lockless) * and the READ_ONCE() in inet_peer_gc() */ WRITE_ONCE(p->dtime, (__u32)jiffies); if (refcount_dec_and_test(&p->refcnt)) call_rcu(&p->rcu, inetpeer_free_rcu); } EXPORT_SYMBOL_GPL(inet_putpeer); /* * Check transmit rate limitation for given message. * The rate information is held in the inet_peer entries now. * This function is generic and could be used for other purposes * too. It uses a Token bucket filter as suggested by Alexey Kuznetsov. * * Note that the same inet_peer fields are modified by functions in * route.c too, but these work for packet destinations while xrlim_allow * works for icmp destinations. This means the rate limiting information * for one "ip object" is shared - and these ICMPs are twice limited: * by source and by destination. * * RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate * SHOULD allow setting of rate limits * * Shared between ICMPv4 and ICMPv6. */ #define XRLIM_BURST_FACTOR 6 bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout) { unsigned long now, token; bool rc = false; if (!peer) return true; token = peer->rate_tokens; now = jiffies; token += now - peer->rate_last; peer->rate_last = now; if (token > XRLIM_BURST_FACTOR * timeout) token = XRLIM_BURST_FACTOR * timeout; if (token >= timeout) { token -= timeout; rc = true; } peer->rate_tokens = token; return rc; } EXPORT_SYMBOL(inet_peer_xrlim_allow); void inetpeer_invalidate_tree(struct inet_peer_base *base) { struct rb_node *p = rb_first(&base->rb_root); while (p) { struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node); p = rb_next(p); rb_erase(&peer->rb_node, &base->rb_root); inet_putpeer(peer); cond_resched(); } base->total = 0; } EXPORT_SYMBOL(inetpeer_invalidate_tree);