511 lines
16 KiB
C
511 lines
16 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/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 <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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* At this moment this information consists only of ID field for the next
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* outgoing IP packet. This field is incremented with each packet as encoded
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* in inet_getid() function (include/net/inetpeer.h).
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* At the moment of writing this notes identifier of IP packets is generated
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* to be unpredictable using this code only for packets subjected
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* (actually or potentially) to defragmentation. I.e. DF packets less than
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* PMTU in size uses a constant ID and do not use this code (see
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* ip_select_ident() in include/net/ip.h).
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*
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* Route cache entries hold references to our nodes.
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* New cache entries get references via lookup by destination IP address in
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* the avl tree. The reference is grabbed only when it's needed i.e. only
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* when we try to output IP packet which needs an unpredictable ID (see
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* __ip_select_ident() in net/ipv4/route.c).
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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 AVL 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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* avl_left, avl_right, avl_parent, avl_height: 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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* ip_id_count: atomic value (no lock needed)
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*/
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static struct kmem_cache *peer_cachep __read_mostly;
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#define node_height(x) x->avl_height
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#define peer_avl_empty ((struct inet_peer *)&peer_fake_node)
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#define peer_avl_empty_rcu ((struct inet_peer __rcu __force *)&peer_fake_node)
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static const struct inet_peer peer_fake_node = {
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.avl_left = peer_avl_empty_rcu,
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.avl_right = peer_avl_empty_rcu,
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.avl_height = 0
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};
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struct inet_peer_base {
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struct inet_peer __rcu *root;
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seqlock_t lock;
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int total;
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};
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static struct inet_peer_base v4_peers = {
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.root = peer_avl_empty_rcu,
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.lock = __SEQLOCK_UNLOCKED(v4_peers.lock),
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.total = 0,
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};
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static struct inet_peer_base v6_peers = {
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.root = peer_avl_empty_rcu,
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.lock = __SEQLOCK_UNLOCKED(v6_peers.lock),
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.total = 0,
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};
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#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
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/* Exported for sysctl_net_ipv4. */
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int inet_peer_threshold __read_mostly = 65536 + 128; /* 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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struct sysinfo si;
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/* Use the straight interface to information about memory. */
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si_meminfo(&si);
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/* The values below were suggested by Alexey Kuznetsov
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* <kuznet@ms2.inr.ac.ru>. I don't have any opinion about the values
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* myself. --SAW
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*/
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if (si.totalram <= (32768*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
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if (si.totalram <= (16384*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 1; /* about 512KB */
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if (si.totalram <= (8192*1024)/PAGE_SIZE)
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inet_peer_threshold >>= 2; /* about 128KB */
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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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static int addr_compare(const struct inetpeer_addr *a,
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const struct inetpeer_addr *b)
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{
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int i, n = (a->family == AF_INET ? 1 : 4);
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for (i = 0; i < n; i++) {
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if (a->addr.a6[i] == b->addr.a6[i])
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continue;
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if (a->addr.a6[i] < b->addr.a6[i])
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return -1;
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return 1;
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}
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return 0;
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}
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#define rcu_deref_locked(X, BASE) \
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rcu_dereference_protected(X, lockdep_is_held(&(BASE)->lock.lock))
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/*
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* Called with local BH disabled and the pool lock held.
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*/
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#define lookup(_daddr, _stack, _base) \
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({ \
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struct inet_peer *u; \
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struct inet_peer __rcu **v; \
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\
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stackptr = _stack; \
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*stackptr++ = &_base->root; \
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for (u = rcu_deref_locked(_base->root, _base); \
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u != peer_avl_empty; ) { \
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int cmp = addr_compare(_daddr, &u->daddr); \
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if (cmp == 0) \
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break; \
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if (cmp == -1) \
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v = &u->avl_left; \
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else \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = rcu_deref_locked(*v, _base); \
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} \
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u; \
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})
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/*
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* Called with rcu_read_lock()
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* Because we hold no lock against a writer, its quite possible we fall
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* in an endless loop.
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* But every pointer we follow is guaranteed to be valid thanks to RCU.
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* We exit from this function if number of links exceeds PEER_MAXDEPTH
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*/
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static struct inet_peer *lookup_rcu(const struct inetpeer_addr *daddr,
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struct inet_peer_base *base)
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{
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struct inet_peer *u = rcu_dereference(base->root);
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int count = 0;
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while (u != peer_avl_empty) {
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int cmp = addr_compare(daddr, &u->daddr);
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if (cmp == 0) {
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/* Before taking a reference, check if this entry was
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* deleted (refcnt=-1)
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*/
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if (!atomic_add_unless(&u->refcnt, 1, -1))
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u = NULL;
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return u;
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}
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if (cmp == -1)
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u = rcu_dereference(u->avl_left);
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else
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u = rcu_dereference(u->avl_right);
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if (unlikely(++count == PEER_MAXDEPTH))
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break;
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}
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return NULL;
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}
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/* Called with local BH disabled and the pool lock held. */
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#define lookup_rightempty(start, base) \
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({ \
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struct inet_peer *u; \
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struct inet_peer __rcu **v; \
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*stackptr++ = &start->avl_left; \
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v = &start->avl_left; \
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for (u = rcu_deref_locked(*v, base); \
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u->avl_right != peer_avl_empty_rcu; ) { \
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v = &u->avl_right; \
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*stackptr++ = v; \
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u = rcu_deref_locked(*v, base); \
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} \
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u; \
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})
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/* Called with local BH disabled and the pool lock held.
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* Variable names are the proof of operation correctness.
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* Look into mm/map_avl.c for more detail description of the ideas.
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*/
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static void peer_avl_rebalance(struct inet_peer __rcu **stack[],
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struct inet_peer __rcu ***stackend,
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struct inet_peer_base *base)
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{
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struct inet_peer __rcu **nodep;
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struct inet_peer *node, *l, *r;
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int lh, rh;
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while (stackend > stack) {
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nodep = *--stackend;
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node = rcu_deref_locked(*nodep, base);
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l = rcu_deref_locked(node->avl_left, base);
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r = rcu_deref_locked(node->avl_right, base);
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lh = node_height(l);
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rh = node_height(r);
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if (lh > rh + 1) { /* l: RH+2 */
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struct inet_peer *ll, *lr, *lrl, *lrr;
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int lrh;
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ll = rcu_deref_locked(l->avl_left, base);
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lr = rcu_deref_locked(l->avl_right, base);
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lrh = node_height(lr);
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if (lrh <= node_height(ll)) { /* ll: RH+1 */
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RCU_INIT_POINTER(node->avl_left, lr); /* lr: RH or RH+1 */
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RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
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node->avl_height = lrh + 1; /* RH+1 or RH+2 */
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RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH+1 */
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RCU_INIT_POINTER(l->avl_right, node); /* node: RH+1 or RH+2 */
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l->avl_height = node->avl_height + 1;
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RCU_INIT_POINTER(*nodep, l);
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} else { /* ll: RH, lr: RH+1 */
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lrl = rcu_deref_locked(lr->avl_left, base);/* lrl: RH or RH-1 */
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lrr = rcu_deref_locked(lr->avl_right, base);/* lrr: RH or RH-1 */
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RCU_INIT_POINTER(node->avl_left, lrr); /* lrr: RH or RH-1 */
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RCU_INIT_POINTER(node->avl_right, r); /* r: RH */
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node->avl_height = rh + 1; /* node: RH+1 */
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RCU_INIT_POINTER(l->avl_left, ll); /* ll: RH */
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RCU_INIT_POINTER(l->avl_right, lrl); /* lrl: RH or RH-1 */
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l->avl_height = rh + 1; /* l: RH+1 */
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RCU_INIT_POINTER(lr->avl_left, l); /* l: RH+1 */
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RCU_INIT_POINTER(lr->avl_right, node); /* node: RH+1 */
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lr->avl_height = rh + 2;
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RCU_INIT_POINTER(*nodep, lr);
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}
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} else if (rh > lh + 1) { /* r: LH+2 */
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struct inet_peer *rr, *rl, *rlr, *rll;
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int rlh;
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rr = rcu_deref_locked(r->avl_right, base);
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rl = rcu_deref_locked(r->avl_left, base);
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rlh = node_height(rl);
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if (rlh <= node_height(rr)) { /* rr: LH+1 */
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RCU_INIT_POINTER(node->avl_right, rl); /* rl: LH or LH+1 */
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RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
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node->avl_height = rlh + 1; /* LH+1 or LH+2 */
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RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH+1 */
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RCU_INIT_POINTER(r->avl_left, node); /* node: LH+1 or LH+2 */
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r->avl_height = node->avl_height + 1;
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RCU_INIT_POINTER(*nodep, r);
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} else { /* rr: RH, rl: RH+1 */
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rlr = rcu_deref_locked(rl->avl_right, base);/* rlr: LH or LH-1 */
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rll = rcu_deref_locked(rl->avl_left, base);/* rll: LH or LH-1 */
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RCU_INIT_POINTER(node->avl_right, rll); /* rll: LH or LH-1 */
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RCU_INIT_POINTER(node->avl_left, l); /* l: LH */
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node->avl_height = lh + 1; /* node: LH+1 */
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RCU_INIT_POINTER(r->avl_right, rr); /* rr: LH */
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RCU_INIT_POINTER(r->avl_left, rlr); /* rlr: LH or LH-1 */
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r->avl_height = lh + 1; /* r: LH+1 */
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RCU_INIT_POINTER(rl->avl_right, r); /* r: LH+1 */
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RCU_INIT_POINTER(rl->avl_left, node); /* node: LH+1 */
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rl->avl_height = lh + 2;
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RCU_INIT_POINTER(*nodep, rl);
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}
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} else {
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node->avl_height = (lh > rh ? lh : rh) + 1;
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}
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}
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}
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/* Called with local BH disabled and the pool lock held. */
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#define link_to_pool(n, base) \
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do { \
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n->avl_height = 1; \
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n->avl_left = peer_avl_empty_rcu; \
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n->avl_right = peer_avl_empty_rcu; \
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/* lockless readers can catch us now */ \
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rcu_assign_pointer(**--stackptr, n); \
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peer_avl_rebalance(stack, stackptr, base); \
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} while (0)
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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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static void unlink_from_pool(struct inet_peer *p, struct inet_peer_base *base,
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struct inet_peer __rcu **stack[PEER_MAXDEPTH])
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{
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struct inet_peer __rcu ***stackptr, ***delp;
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if (lookup(&p->daddr, stack, base) != p)
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BUG();
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delp = stackptr - 1; /* *delp[0] == p */
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if (p->avl_left == peer_avl_empty_rcu) {
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*delp[0] = p->avl_right;
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--stackptr;
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} else {
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/* look for a node to insert instead of p */
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struct inet_peer *t;
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t = lookup_rightempty(p, base);
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BUG_ON(rcu_deref_locked(*stackptr[-1], base) != t);
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**--stackptr = t->avl_left;
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/* t is removed, t->daddr > x->daddr for any
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* x in p->avl_left subtree.
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* Put t in the old place of p. */
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RCU_INIT_POINTER(*delp[0], t);
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t->avl_left = p->avl_left;
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t->avl_right = p->avl_right;
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t->avl_height = p->avl_height;
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BUG_ON(delp[1] != &p->avl_left);
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delp[1] = &t->avl_left; /* was &p->avl_left */
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}
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peer_avl_rebalance(stack, stackptr, base);
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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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static struct inet_peer_base *family_to_base(int family)
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{
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return family == AF_INET ? &v4_peers : &v6_peers;
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}
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/* perform garbage collect on all items stacked during a lookup */
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static int inet_peer_gc(struct inet_peer_base *base,
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struct inet_peer __rcu **stack[PEER_MAXDEPTH],
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struct inet_peer __rcu ***stackptr)
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{
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struct inet_peer *p, *gchead = NULL;
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__u32 delta, ttl;
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int cnt = 0;
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if (base->total >= inet_peer_threshold)
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ttl = 0; /* be aggressive */
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else
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ttl = inet_peer_maxttl
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- (inet_peer_maxttl - inet_peer_minttl) / HZ *
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base->total / inet_peer_threshold * HZ;
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stackptr--; /* last stack slot is peer_avl_empty */
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while (stackptr > stack) {
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stackptr--;
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p = rcu_deref_locked(**stackptr, base);
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if (atomic_read(&p->refcnt) == 0) {
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smp_rmb();
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delta = (__u32)jiffies - p->dtime;
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if (delta >= ttl &&
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atomic_cmpxchg(&p->refcnt, 0, -1) == 0) {
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p->gc_next = gchead;
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gchead = p;
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}
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}
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}
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while ((p = gchead) != NULL) {
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gchead = p->gc_next;
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cnt++;
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unlink_from_pool(p, base, stack);
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}
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return cnt;
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}
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struct inet_peer *inet_getpeer(const struct inetpeer_addr *daddr, int create)
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{
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struct inet_peer __rcu **stack[PEER_MAXDEPTH], ***stackptr;
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struct inet_peer_base *base = family_to_base(daddr->family);
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struct inet_peer *p;
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unsigned int sequence;
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int invalidated, gccnt = 0;
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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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sequence = read_seqbegin(&base->lock);
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p = lookup_rcu(daddr, base);
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invalidated = read_seqretry(&base->lock, sequence);
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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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write_seqlock_bh(&base->lock);
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relookup:
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p = lookup(daddr, stack, base);
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if (p != peer_avl_empty) {
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atomic_inc(&p->refcnt);
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write_sequnlock_bh(&base->lock);
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return p;
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}
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if (!gccnt) {
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gccnt = inet_peer_gc(base, stack, stackptr);
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if (gccnt && create)
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goto relookup;
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}
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p = create ? kmem_cache_alloc(peer_cachep, GFP_ATOMIC) : NULL;
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if (p) {
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p->daddr = *daddr;
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atomic_set(&p->refcnt, 1);
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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;
|
|
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);
|