diff options
Diffstat (limited to 'net/ipv4/inetpeer.c')
| -rw-r--r-- | net/ipv4/inetpeer.c | 460 |
1 files changed, 460 insertions, 0 deletions
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c new file mode 100644 index 00000000000..95473953c40 --- /dev/null +++ b/net/ipv4/inetpeer.c @@ -0,0 +1,460 @@ +/* + * INETPEER - A storage for permanent information about peers + * + * This source is covered by the GNU GPL, the same as all kernel sources. + * + * Version: $Id: inetpeer.c,v 1.7 2001/09/20 21:22:50 davem Exp $ + * + * 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/sched.h> +#include <linux/timer.h> +#include <linux/time.h> +#include <linux/kernel.h> +#include <linux/mm.h> +#include <linux/net.h> +#include <net/inetpeer.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 write lock held. + * 2. Nodes may disappear from the tree only with the pool write lock held + * AND reference count being 0. + * 3. Nodes appears and disappears from unused node list only under + * "inet_peer_unused_lock". + * 4. Global variable peer_total is modified under the pool lock. + * 5. struct inet_peer fields modification: + * avl_left, avl_right, avl_parent, avl_height: pool lock + * unused_next, unused_prevp: unused node list lock + * refcnt: atomically against modifications on other CPU; + * usually under some other lock to prevent node disappearing + * dtime: unused node list lock + * v4daddr: unchangeable + * ip_id_count: idlock + */ + +/* Exported for inet_getid inline function. */ +DEFINE_SPINLOCK(inet_peer_idlock); + +static kmem_cache_t *peer_cachep; + +#define node_height(x) x->avl_height +static struct inet_peer peer_fake_node = { + .avl_left = &peer_fake_node, + .avl_right = &peer_fake_node, + .avl_height = 0 +}; +#define peer_avl_empty (&peer_fake_node) +static struct inet_peer *peer_root = peer_avl_empty; +static DEFINE_RWLOCK(peer_pool_lock); +#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */ + +static volatile int peer_total; +/* Exported for sysctl_net_ipv4. */ +int inet_peer_threshold = 65536 + 128; /* start to throw entries more + * aggressively at this stage */ +int inet_peer_minttl = 120 * HZ; /* TTL under high load: 120 sec */ +int inet_peer_maxttl = 10 * 60 * HZ; /* usual time to live: 10 min */ + +static struct inet_peer *inet_peer_unused_head; +/* Exported for inet_putpeer inline function. */ +struct inet_peer **inet_peer_unused_tailp = &inet_peer_unused_head; +DEFINE_SPINLOCK(inet_peer_unused_lock); +#define PEER_MAX_CLEANUP_WORK 30 + +static void peer_check_expire(unsigned long dummy); +static struct timer_list peer_periodic_timer = + TIMER_INITIALIZER(peer_check_expire, 0, 0); + +/* Exported for sysctl_net_ipv4. */ +int inet_peer_gc_mintime = 10 * HZ, + inet_peer_gc_maxtime = 120 * HZ; + +/* 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, + NULL, NULL); + + if (!peer_cachep) + panic("cannot create inet_peer_cache"); + + /* All the timers, started at system startup tend + to synchronize. Perturb it a bit. + */ + peer_periodic_timer.expires = jiffies + + net_random() % inet_peer_gc_maxtime + + inet_peer_gc_maxtime; + add_timer(&peer_periodic_timer); +} + +/* Called with or without local BH being disabled. */ +static void unlink_from_unused(struct inet_peer *p) +{ + spin_lock_bh(&inet_peer_unused_lock); + if (p->unused_prevp != NULL) { + /* On unused list. */ + *p->unused_prevp = p->unused_next; + if (p->unused_next != NULL) + p->unused_next->unused_prevp = p->unused_prevp; + else + inet_peer_unused_tailp = p->unused_prevp; + p->unused_prevp = NULL; /* mark it as removed */ + } + spin_unlock_bh(&inet_peer_unused_lock); +} + +/* Called with local BH disabled and the pool lock held. */ +#define lookup(daddr) \ +({ \ + struct inet_peer *u, **v; \ + stackptr = stack; \ + *stackptr++ = &peer_root; \ + for (u = peer_root; u != peer_avl_empty; ) { \ + if (daddr == u->v4daddr) \ + break; \ + if (daddr < u->v4daddr) \ + v = &u->avl_left; \ + else \ + v = &u->avl_right; \ + *stackptr++ = v; \ + u = *v; \ + } \ + u; \ +}) + +/* Called with local BH disabled and the pool write lock held. */ +#define lookup_rightempty(start) \ +({ \ + struct inet_peer *u, **v; \ + *stackptr++ = &start->avl_left; \ + v = &start->avl_left; \ + for (u = *v; u->avl_right != peer_avl_empty; ) { \ + v = &u->avl_right; \ + *stackptr++ = v; \ + u = *v; \ + } \ + u; \ +}) + +/* Called with local BH disabled and the pool write 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 **stack[], + struct inet_peer ***stackend) +{ + struct inet_peer **nodep, *node, *l, *r; + int lh, rh; + + while (stackend > stack) { + nodep = *--stackend; + node = *nodep; + l = node->avl_left; + r = node->avl_right; + 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 = l->avl_left; + lr = l->avl_right; + lrh = node_height(lr); + if (lrh <= node_height(ll)) { /* ll: RH+1 */ + node->avl_left = lr; /* lr: RH or RH+1 */ + node->avl_right = r; /* r: RH */ + node->avl_height = lrh + 1; /* RH+1 or RH+2 */ + l->avl_left = ll; /* ll: RH+1 */ + l->avl_right = node; /* node: RH+1 or RH+2 */ + l->avl_height = node->avl_height + 1; + *nodep = l; + } else { /* ll: RH, lr: RH+1 */ + lrl = lr->avl_left; /* lrl: RH or RH-1 */ + lrr = lr->avl_right; /* lrr: RH or RH-1 */ + node->avl_left = lrr; /* lrr: RH or RH-1 */ + node->avl_right = r; /* r: RH */ + node->avl_height = rh + 1; /* node: RH+1 */ + l->avl_left = ll; /* ll: RH */ + l->avl_right = lrl; /* lrl: RH or RH-1 */ + l->avl_height = rh + 1; /* l: RH+1 */ + lr->avl_left = l; /* l: RH+1 */ + lr->avl_right = node; /* node: RH+1 */ + lr->avl_height = rh + 2; + *nodep = lr; + } + } else if (rh > lh + 1) { /* r: LH+2 */ + struct inet_peer *rr, *rl, *rlr, *rll; + int rlh; + rr = r->avl_right; + rl = r->avl_left; + rlh = node_height(rl); + if (rlh <= node_height(rr)) { /* rr: LH+1 */ + node->avl_right = rl; /* rl: LH or LH+1 */ + node->avl_left = l; /* l: LH */ + node->avl_height = rlh + 1; /* LH+1 or LH+2 */ + r->avl_right = rr; /* rr: LH+1 */ + r->avl_left = node; /* node: LH+1 or LH+2 */ + r->avl_height = node->avl_height + 1; + *nodep = r; + } else { /* rr: RH, rl: RH+1 */ + rlr = rl->avl_right; /* rlr: LH or LH-1 */ + rll = rl->avl_left; /* rll: LH or LH-1 */ + node->avl_right = rll; /* rll: LH or LH-1 */ + node->avl_left = l; /* l: LH */ + node->avl_height = lh + 1; /* node: LH+1 */ + r->avl_right = rr; /* rr: LH */ + r->avl_left = rlr; /* rlr: LH or LH-1 */ + r->avl_height = lh + 1; /* r: LH+1 */ + rl->avl_right = r; /* r: LH+1 */ + rl->avl_left = node; /* node: LH+1 */ + rl->avl_height = lh + 2; + *nodep = rl; + } + } else { + node->avl_height = (lh > rh ? lh : rh) + 1; + } + } +} + +/* Called with local BH disabled and the pool write lock held. */ +#define link_to_pool(n) \ +do { \ + n->avl_height = 1; \ + n->avl_left = peer_avl_empty; \ + n->avl_right = peer_avl_empty; \ + **--stackptr = n; \ + peer_avl_rebalance(stack, stackptr); \ +} while(0) + +/* May be called with local BH enabled. */ +static void unlink_from_pool(struct inet_peer *p) +{ + int do_free; + + do_free = 0; + + write_lock_bh(&peer_pool_lock); + /* Check the reference counter. It was artificially incremented by 1 + * in cleanup() function to prevent sudden disappearing. If the + * reference count is still 1 then the node is referenced only as `p' + * here and from the pool. So under the exclusive pool lock it's safe + * to remove the node and free it later. */ + if (atomic_read(&p->refcnt) == 1) { + struct inet_peer **stack[PEER_MAXDEPTH]; + struct inet_peer ***stackptr, ***delp; + if (lookup(p->v4daddr) != p) + BUG(); + delp = stackptr - 1; /* *delp[0] == p */ + if (p->avl_left == peer_avl_empty) { + *delp[0] = p->avl_right; + --stackptr; + } else { + /* look for a node to insert instead of p */ + struct inet_peer *t; + t = lookup_rightempty(p); + if (*stackptr[-1] != t) + BUG(); + **--stackptr = t->avl_left; + /* t is removed, t->v4daddr > x->v4daddr for any + * x in p->avl_left subtree. + * Put t in the old place of p. */ + *delp[0] = t; + t->avl_left = p->avl_left; + t->avl_right = p->avl_right; + t->avl_height = p->avl_height; + if (delp[1] != &p->avl_left) + BUG(); + delp[1] = &t->avl_left; /* was &p->avl_left */ + } + peer_avl_rebalance(stack, stackptr); + peer_total--; + do_free = 1; + } + write_unlock_bh(&peer_pool_lock); + + if (do_free) + kmem_cache_free(peer_cachep, p); + else + /* The node is used again. Decrease the reference counter + * back. The loop "cleanup -> unlink_from_unused + * -> unlink_from_pool -> putpeer -> link_to_unused + * -> cleanup (for the same node)" + * doesn't really exist because the entry will have a + * recent deletion time and will not be cleaned again soon. */ + inet_putpeer(p); +} + +/* May be called with local BH enabled. */ +static int cleanup_once(unsigned long ttl) +{ + struct inet_peer *p; + + /* Remove the first entry from the list of unused nodes. */ + spin_lock_bh(&inet_peer_unused_lock); + p = inet_peer_unused_head; + if (p != NULL) { + if (time_after(p->dtime + ttl, jiffies)) { + /* Do not prune fresh entries. */ + spin_unlock_bh(&inet_peer_unused_lock); + return -1; + } + inet_peer_unused_head = p->unused_next; + if (p->unused_next != NULL) + p->unused_next->unused_prevp = p->unused_prevp; + else + inet_peer_unused_tailp = p->unused_prevp; + p->unused_prevp = NULL; /* mark as not on the list */ + /* Grab an extra reference to prevent node disappearing + * before unlink_from_pool() call. */ + atomic_inc(&p->refcnt); + } + spin_unlock_bh(&inet_peer_unused_lock); + + if (p == NULL) + /* It means that the total number of USED entries has + * grown over inet_peer_threshold. It shouldn't really + * happen because of entry limits in route cache. */ + return -1; + + unlink_from_pool(p); + return 0; +} + +/* Called with or without local BH being disabled. */ +struct inet_peer *inet_getpeer(__u32 daddr, int create) +{ + struct inet_peer *p, *n; + struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr; + + /* Look up for the address quickly. */ + read_lock_bh(&peer_pool_lock); + p = lookup(daddr); + if (p != peer_avl_empty) + atomic_inc(&p->refcnt); + read_unlock_bh(&peer_pool_lock); + + if (p != peer_avl_empty) { + /* The existing node has been found. */ + /* Remove the entry from unused list if it was there. */ + unlink_from_unused(p); + return p; + } + + if (!create) + return NULL; + + /* Allocate the space outside the locked region. */ + n = kmem_cache_alloc(peer_cachep, GFP_ATOMIC); + if (n == NULL) + return NULL; + n->v4daddr = daddr; + atomic_set(&n->refcnt, 1); + n->ip_id_count = secure_ip_id(daddr); + n->tcp_ts_stamp = 0; + + write_lock_bh(&peer_pool_lock); + /* Check if an entry has suddenly appeared. */ + p = lookup(daddr); + if (p != peer_avl_empty) + goto out_free; + + /* Link the node. */ + link_to_pool(n); + n->unused_prevp = NULL; /* not on the list */ + peer_total++; + write_unlock_bh(&peer_pool_lock); + + if (peer_total >= inet_peer_threshold) + /* Remove one less-recently-used entry. */ + cleanup_once(0); + + return n; + +out_free: + /* The appropriate node is already in the pool. */ + atomic_inc(&p->refcnt); + write_unlock_bh(&peer_pool_lock); + /* Remove the entry from unused list if it was there. */ + unlink_from_unused(p); + /* Free preallocated the preallocated node. */ + kmem_cache_free(peer_cachep, n); + return p; +} + +/* Called with local BH disabled. */ +static void peer_check_expire(unsigned long dummy) +{ + int i; + int ttl; + + if (peer_total >= inet_peer_threshold) + ttl = inet_peer_minttl; + else + ttl = inet_peer_maxttl + - (inet_peer_maxttl - inet_peer_minttl) / HZ * + peer_total / inet_peer_threshold * HZ; + for (i = 0; i < PEER_MAX_CLEANUP_WORK && !cleanup_once(ttl); i++); + + /* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime + * interval depending on the total number of entries (more entries, + * less interval). */ + peer_periodic_timer.expires = jiffies + + inet_peer_gc_maxtime + - (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ * + peer_total / inet_peer_threshold * HZ; + add_timer(&peer_periodic_timer); +} + +EXPORT_SYMBOL(inet_peer_idlock); |