/*
* 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; /* 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(inet_peer, SLAB_HWCACHE_ALIGN | SLAB_PANIC);
}
/* 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);
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