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![Kuniyuki Iwashima](/assets/img/avatar_default.png)
While reading inetpeer sysctl variables, they can be changed
concurrently. So, we need to add READ_ONCE() to avoid data-races.
Fixes: 1da177e4c3
("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
308 lines
8.3 KiB
C
308 lines
8.3 KiB
C
/*
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* INETPEER - A storage for permanent information about peers
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*
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* This source is covered by the GNU GPL, the same as all kernel sources.
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*
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* Authors: Andrey V. Savochkin <saw@msu.ru>
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*/
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#include <linux/cache.h>
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/slab.h>
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#include <linux/interrupt.h>
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#include <linux/spinlock.h>
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#include <linux/random.h>
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#include <linux/timer.h>
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#include <linux/time.h>
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#include <linux/kernel.h>
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#include <linux/mm.h>
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#include <linux/net.h>
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#include <linux/workqueue.h>
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#include <net/ip.h>
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#include <net/inetpeer.h>
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#include <net/secure_seq.h>
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/*
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* Theory of operations.
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* We keep one entry for each peer IP address. The nodes contains long-living
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* information about the peer which doesn't depend on routes.
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*
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* Nodes are removed only when reference counter goes to 0.
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* When it's happened the node may be removed when a sufficient amount of
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* time has been passed since its last use. The less-recently-used entry can
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* also be removed if the pool is overloaded i.e. if the total amount of
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* entries is greater-or-equal than the threshold.
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*
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* Node pool is organised as an RB tree.
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* Such an implementation has been chosen not just for fun. It's a way to
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* prevent easy and efficient DoS attacks by creating hash collisions. A huge
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* amount of long living nodes in a single hash slot would significantly delay
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* lookups performed with disabled BHs.
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*
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* Serialisation issues.
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* 1. Nodes may appear in the tree only with the pool lock held.
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* 2. Nodes may disappear from the tree only with the pool lock held
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* AND reference count being 0.
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* 3. Global variable peer_total is modified under the pool lock.
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* 4. struct inet_peer fields modification:
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* rb_node: pool lock
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* refcnt: atomically against modifications on other CPU;
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* usually under some other lock to prevent node disappearing
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* daddr: unchangeable
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*/
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static struct kmem_cache *peer_cachep __ro_after_init;
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void inet_peer_base_init(struct inet_peer_base *bp)
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{
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bp->rb_root = RB_ROOT;
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seqlock_init(&bp->lock);
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bp->total = 0;
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}
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EXPORT_SYMBOL_GPL(inet_peer_base_init);
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#define PEER_MAX_GC 32
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/* Exported for sysctl_net_ipv4. */
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int inet_peer_threshold __read_mostly; /* start to throw entries more
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* aggressively at this stage */
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int inet_peer_minttl __read_mostly = 120 * HZ; /* TTL under high load: 120 sec */
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int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min */
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/* Called from ip_output.c:ip_init */
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void __init inet_initpeers(void)
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{
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u64 nr_entries;
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/* 1% of physical memory */
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nr_entries = div64_ul((u64)totalram_pages() << PAGE_SHIFT,
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100 * L1_CACHE_ALIGN(sizeof(struct inet_peer)));
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inet_peer_threshold = clamp_val(nr_entries, 4096, 65536 + 128);
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peer_cachep = kmem_cache_create("inet_peer_cache",
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sizeof(struct inet_peer),
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0, SLAB_HWCACHE_ALIGN | SLAB_PANIC,
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NULL);
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}
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/* Called with rcu_read_lock() or base->lock held */
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static struct inet_peer *lookup(const struct inetpeer_addr *daddr,
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struct inet_peer_base *base,
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unsigned int seq,
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struct inet_peer *gc_stack[],
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unsigned int *gc_cnt,
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struct rb_node **parent_p,
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struct rb_node ***pp_p)
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{
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struct rb_node **pp, *parent, *next;
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struct inet_peer *p;
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pp = &base->rb_root.rb_node;
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parent = NULL;
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while (1) {
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int cmp;
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next = rcu_dereference_raw(*pp);
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if (!next)
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break;
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parent = next;
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p = rb_entry(parent, struct inet_peer, rb_node);
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cmp = inetpeer_addr_cmp(daddr, &p->daddr);
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if (cmp == 0) {
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if (!refcount_inc_not_zero(&p->refcnt))
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break;
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return p;
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}
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if (gc_stack) {
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if (*gc_cnt < PEER_MAX_GC)
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gc_stack[(*gc_cnt)++] = p;
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} else if (unlikely(read_seqretry(&base->lock, seq))) {
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break;
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}
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if (cmp == -1)
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pp = &next->rb_left;
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else
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pp = &next->rb_right;
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}
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*parent_p = parent;
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*pp_p = pp;
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return NULL;
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}
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static void inetpeer_free_rcu(struct rcu_head *head)
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{
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kmem_cache_free(peer_cachep, container_of(head, struct inet_peer, rcu));
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}
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/* perform garbage collect on all items stacked during a lookup */
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static void inet_peer_gc(struct inet_peer_base *base,
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struct inet_peer *gc_stack[],
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unsigned int gc_cnt)
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{
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int peer_threshold, peer_maxttl, peer_minttl;
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struct inet_peer *p;
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__u32 delta, ttl;
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int i;
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peer_threshold = READ_ONCE(inet_peer_threshold);
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peer_maxttl = READ_ONCE(inet_peer_maxttl);
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peer_minttl = READ_ONCE(inet_peer_minttl);
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if (base->total >= peer_threshold)
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ttl = 0; /* be aggressive */
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else
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ttl = peer_maxttl - (peer_maxttl - peer_minttl) / HZ *
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base->total / peer_threshold * HZ;
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for (i = 0; i < gc_cnt; i++) {
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p = gc_stack[i];
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/* The READ_ONCE() pairs with the WRITE_ONCE()
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* in inet_putpeer()
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*/
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delta = (__u32)jiffies - READ_ONCE(p->dtime);
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if (delta < ttl || !refcount_dec_if_one(&p->refcnt))
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gc_stack[i] = NULL;
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}
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for (i = 0; i < gc_cnt; i++) {
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p = gc_stack[i];
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if (p) {
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rb_erase(&p->rb_node, &base->rb_root);
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base->total--;
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call_rcu(&p->rcu, inetpeer_free_rcu);
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}
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}
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}
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struct inet_peer *inet_getpeer(struct inet_peer_base *base,
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const struct inetpeer_addr *daddr,
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int create)
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{
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struct inet_peer *p, *gc_stack[PEER_MAX_GC];
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struct rb_node **pp, *parent;
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unsigned int gc_cnt, seq;
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int invalidated;
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/* Attempt a lockless lookup first.
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* Because of a concurrent writer, we might not find an existing entry.
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*/
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rcu_read_lock();
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seq = read_seqbegin(&base->lock);
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p = lookup(daddr, base, seq, NULL, &gc_cnt, &parent, &pp);
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invalidated = read_seqretry(&base->lock, seq);
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rcu_read_unlock();
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if (p)
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return p;
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/* If no writer did a change during our lookup, we can return early. */
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if (!create && !invalidated)
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return NULL;
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/* retry an exact lookup, taking the lock before.
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* At least, nodes should be hot in our cache.
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*/
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parent = NULL;
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write_seqlock_bh(&base->lock);
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gc_cnt = 0;
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p = lookup(daddr, base, seq, gc_stack, &gc_cnt, &parent, &pp);
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if (!p && create) {
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p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
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if (p) {
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p->daddr = *daddr;
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p->dtime = (__u32)jiffies;
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refcount_set(&p->refcnt, 2);
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atomic_set(&p->rid, 0);
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p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
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p->rate_tokens = 0;
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p->n_redirects = 0;
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/* 60*HZ is arbitrary, but chosen enough high so that the first
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* calculation of tokens is at its maximum.
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*/
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p->rate_last = jiffies - 60*HZ;
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rb_link_node(&p->rb_node, parent, pp);
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rb_insert_color(&p->rb_node, &base->rb_root);
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base->total++;
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}
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}
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if (gc_cnt)
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inet_peer_gc(base, gc_stack, gc_cnt);
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write_sequnlock_bh(&base->lock);
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return p;
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}
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EXPORT_SYMBOL_GPL(inet_getpeer);
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void inet_putpeer(struct inet_peer *p)
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{
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/* The WRITE_ONCE() pairs with itself (we run lockless)
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* and the READ_ONCE() in inet_peer_gc()
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*/
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WRITE_ONCE(p->dtime, (__u32)jiffies);
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if (refcount_dec_and_test(&p->refcnt))
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call_rcu(&p->rcu, inetpeer_free_rcu);
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}
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EXPORT_SYMBOL_GPL(inet_putpeer);
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/*
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* Check transmit rate limitation for given message.
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* The rate information is held in the inet_peer entries now.
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* This function is generic and could be used for other purposes
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* too. It uses a Token bucket filter as suggested by Alexey Kuznetsov.
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*
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* Note that the same inet_peer fields are modified by functions in
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* route.c too, but these work for packet destinations while xrlim_allow
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* works for icmp destinations. This means the rate limiting information
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* for one "ip object" is shared - and these ICMPs are twice limited:
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* by source and by destination.
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*
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* RFC 1812: 4.3.2.8 SHOULD be able to limit error message rate
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* SHOULD allow setting of rate limits
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*
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* Shared between ICMPv4 and ICMPv6.
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*/
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#define XRLIM_BURST_FACTOR 6
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bool inet_peer_xrlim_allow(struct inet_peer *peer, int timeout)
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{
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unsigned long now, token;
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bool rc = false;
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if (!peer)
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return true;
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token = peer->rate_tokens;
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now = jiffies;
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token += now - peer->rate_last;
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peer->rate_last = now;
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if (token > XRLIM_BURST_FACTOR * timeout)
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token = XRLIM_BURST_FACTOR * timeout;
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if (token >= timeout) {
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token -= timeout;
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rc = true;
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}
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peer->rate_tokens = token;
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return rc;
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}
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EXPORT_SYMBOL(inet_peer_xrlim_allow);
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void inetpeer_invalidate_tree(struct inet_peer_base *base)
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{
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struct rb_node *p = rb_first(&base->rb_root);
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while (p) {
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struct inet_peer *peer = rb_entry(p, struct inet_peer, rb_node);
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p = rb_next(p);
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rb_erase(&peer->rb_node, &base->rb_root);
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inet_putpeer(peer);
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cond_resched();
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}
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base->total = 0;
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}
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EXPORT_SYMBOL(inetpeer_invalidate_tree);
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