/*
* 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 <saw@msu.ru>
*/
#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 <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.
* 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. Global variable peer_total is modified under the pool lock.
* 4. struct inet_peer fields modification:
* avl_left, avl_right, avl_parent, avl_height: pool lock
* refcnt: atomically against modifications on other CPU;
* usually under some other lock to prevent node disappearing
* 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
};
struct inet_peer_base {
struct inet_peer __rcu *root;
seqlock_t lock;
int total;
};
static struct inet_peer_base v4_peers = {
.root = peer_avl_empty_rcu,
.lock = __SEQLOCK_UNLOCKED(v4_peers.lock),
.total = 0,
};
static struct inet_peer_base v6_peers = {
.root = peer_avl_empty_rcu,
.lock = __SEQLOCK_UNLOCKED(v6_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 */
/* 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
* <kuznet@ms2.inr.ac.ru>. 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);
}
static int addr_compare(const struct inetpeer_addr *a,
const struct inetpeer_addr *b)
{
int i, n = (a->family == AF_INET ? 1 : 4);
for (i = 0; i < n; i++) {
if (a->addr.a6[i] == b->addr.a6[i])
continue;
if ((__force u32)a->addr.a6[i] < (__force u32)b->addr.a6[i])
return -1;
return 1;
}
return 0;
}
#define rcu_deref_locked(X, BASE) \
rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.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_deref_locked(_base->root, _base); \
u != peer_avl_empty; ) { \
int cmp = addr_compare(_daddr, &u->daddr); \
if (cmp == 0) \
break; \
if (cmp == -1) \
v = &u->avl_left; \
else \
v = &u->avl_right; \
*stackptr++ = v; \
u = rcu_deref_locked(*v, _base); \
} \
u; \
})
/*
* Called with rcu_read_lock()
* 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(const struct inetpeer_addr *daddr,
struct inet_peer_base *base)
{
struct inet_peer *u = rcu_dereference(base->root);
int count = 0;
while (u != peer_avl_empty) {
int cmp = addr_compare(daddr, &u->daddr);
if (cmp == 0) {
/* Before taking a reference, check if this entry was
* deleted (refcnt=-1)
*/
if (!atomic_add_unless(&u->refcnt, 1, -1))
u = NULL;
return u;
}
if (cmp == -1)
u = rcu_dereference(u->avl_left);
else
u = rcu_dereference(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_deref_locked(*v, base); \
u->avl_right != peer_avl_empty_rcu; ) { \
v = &u->avl_right; \
*stackptr++ = v; \
u = rcu_deref_locked(*v, base); \
} \
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_deref_locked(*nodep, base);
l = rcu_deref_locked(node->avl_left, base);
r = rcu_deref_locked(node->avl_right, base);
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_deref_locked(l->avl_left, base);
lr = rcu_deref_locked(l->avl_right, base);
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_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
lrr = rcu_deref_locked(lr->avl_right, base);/* 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_deref_locked(r->avl_right, base);
rl = rcu_deref_locked(r->avl_left, base);
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_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
rll = rcu_deref_locked(rl->avl_left, base);/* 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));
}
static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
struct inet_peer __rcu **stack[PEER_MAXDEPTH])
{
struct inet_peer __rcu ***stackptr, ***delp;
if (lookup(&p->daddr, 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_deref_locked(*stackptr[-1], base) != 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--;
call_rcu(&p->rcu, inetpeer_free_rcu);
}
static struct inet_peer_base *family_to_base(int family)
{
return family == AF_INET ? &v4_peers : &v6_peers;
}
/* perform garbage collect on all items stacked during a lookup */
static int inet_peer_gc(struct inet_peer_base *base,
struct inet_peer __rcu **stack[PEER_MAXDEPTH],
struct inet_peer __rcu ***stackptr)
{
struct inet_peer *p, *gchead = NULL;
__u32 delta, ttl;
int cnt = 0;
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;
stackptr--; /* last stack slot is peer_avl_empty */
while (stackptr > stack) {
stackptr--;
p = rcu_deref_locked(**stackptr, base);
if (atomic_read(&p->refcnt) == 0) {
smp_rmb();
delta = (__u32)jiffies - p->dtime;
if (delta >= ttl &&
atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
p->gc_next = gchead;
gchead = p;
}
}
}
while ((p = gchead) != NULL) {
gchead = p->gc_next;
cnt++;
unlink_from_pool(p, base, stack);
}
return cnt;
}
struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create)
{
struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
struct inet_peer_base *base = family_to_base(daddr->family);
struct inet_peer *p;
unsigned int sequence;
int invalidated, gccnt = 0;
/* Attempt a lockless lookup first.
* Because of a concurrent writer, we might not find an existing entry.
*/
rcu_read_lock();
sequence = read_seqbegin(&base->lock);
p = lookup_rcu(daddr, base);
invalidated = read_seqretry(&base->lock, sequence);
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.
*/
write_seqlock_bh(&base->lock);
relookup:
p = lookup(daddr, stack, base);
if (p != peer_avl_empty) {
atomic_inc(&p->refcnt);
write_sequnlock_bh(&base->lock);
return p;
}
if (!gccnt) {
gccnt = inet_peer_gc(base, stack, stackptr);
if (gccnt && create)
goto relookup;
}
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,
(daddr->family == AF_INET) ?
secure_ip_id(daddr->addr.a4) :
secure_ipv6_id(daddr->addr.a6));
p->tcp_ts_stamp = 0;
p->metrics[RTAX_LOCK-1] = INETPEER_METRICS_NEW;
p->rate_tokens = 0;
p->rate_last = 0;
p->pmtu_expires = 0;
p->pmtu_orig = 0;
p->redirect_genid = 0;
memset(&p->redirect_learned, 0, sizeof(p->redirect_learned));
/* Link the node. */
link_to_pool(p, base);
base->total++;
}
write_sequnlock_bh(&base->lock);
return p;
}
EXPORT_SYMBOL_GPL(inet_getpeer);
void inet_putpeer(struct inet_peer *p)
{
p->dtime = (__u32)jiffies;
smp_mb__before_atomic_dec();
atomic_dec(&p->refcnt);
}
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);
