net/ipv4/inetpeer.c - kernel/common - Git at Google

 /*
  *		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 <[email protected]>
  */

 #include <linux/cache.h>
 #include <linux/module.h>
 #include <linux/types.h>
 #include <linux/slab.h>
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 #include <linux/random.h>
 #include <linux/timer.h>
 #include <linux/time.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/net.h>
 #include <linux/workqueue.h>
 #include <net/ip.h>
 #include <net/inetpeer.h>
 #include <net/secure_seq.h>

 /*
  *  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 = 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 */

 /* 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
 	 * <[email protected]>.  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);
 }

 /* 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)
 {
 	struct inet_peer *p;
 	__u32 delta, ttl;
 	int i;

 	if (base->total >= inet_peer_threshold)
 		ttl = 0; /* be aggressive */
 	else
 		ttl = inet_peer_maxttl
 				- (inet_peer_maxttl - inet_peer_minttl) / HZ *
 					base->total / inet_peer_threshold * HZ;
 	for (i = 0; i < gc_cnt; i++) {
 		p = gc_stack[i];
 		delta = (__u32)jiffies - 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)
 {
 	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);
	/*
	* 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 <[email protected]>
	*/

	#include <linux/cache.h>
	#include <linux/module.h>
	#include <linux/types.h>
	#include <linux/slab.h>
	#include <linux/interrupt.h>
	#include <linux/spinlock.h>
	#include <linux/random.h>
	#include <linux/timer.h>
	#include <linux/time.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/net.h>
	#include <linux/workqueue.h>
	#include <net/ip.h>
	#include <net/inetpeer.h>
	#include <net/secure_seq.h>

	/*
	* 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 = 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 */

	/* 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
	* <[email protected]>. 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);
	}

	/* 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)
	{
	struct inet_peer *p;
	__u32 delta, ttl;
	int i;

	if (base->total >= inet_peer_threshold)
	ttl = 0; /* be aggressive */
	else
	ttl = inet_peer_maxttl
	- (inet_peer_maxttl - inet_peer_minttl) / HZ *
	base->total / inet_peer_threshold * HZ;
	for (i = 0; i < gc_cnt; i++) {
	p = gc_stack[i];
	delta = (__u32)jiffies - 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)
	{
	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);