patch-2.3.37 linux/net/ipv4/inetpeer.c

• Lines: 448
• Date: Thu Jan 6 10:14:36 2000
• Orig file: v2.3.36/linux/net/ipv4/inetpeer.c
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.36/linux/net/ipv4/inetpeer.c linux/net/ipv4/inetpeer.c
@@ -0,0 +1,447 @@
+/*
+ *		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 1.1 2000/01/06 00:41:55 davem Exp $
+ *
+ *  Authors:	Andrey V. Savochkin <saw@msu.ru>
+ */
+
+#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 <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
+ */
+
+spinlock_t inet_peer_idlock = SPIN_LOCK_UNLOCKED;
+
+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 rwlock_t peer_pool_lock = RW_LOCK_UNLOCKED;
+#define PEER_MAXDEPTH 40 /* sufficient for about 2^27 nodes */
+
+static volatile int peer_total = 0;
+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 */
+struct inet_peer *inet_peer_unused_head = NULL,
+		**inet_peer_unused_tailp = &inet_peer_unused_head;
+spinlock_t inet_peer_unused_lock = SPIN_LOCK_UNLOCKED;
+#define PEER_MAX_CLEANUP_WORK 30
+
+static void peer_check_expire(unsigned long dummy);
+static struct timer_list peer_periodic_timer =
+	{ NULL, NULL, 0, 0, &peer_check_expire };
+int inet_peer_gc_mintime = 10 * HZ,
+    inet_peer_gc_maxtime = 120 * HZ;
+
+
+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)
+		inet_peer_threshold >>= 1; /* max pool size about 1MB on IA32 */
+	if (si.totalram <= 16384*1024)
+		inet_peer_threshold >>= 1; /* about 512KB */
+	if (si.totalram <= 8192*1024)
+		inet_peer_threshold >>= 2; /* about 128KB */
+
+	peer_cachep = kmem_cache_create("inet_peer_cache",
+			sizeof(struct inet_peer),
+			0, SLAB_HWCACHE_ALIGN,
+			NULL, NULL);
+
+	/* 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);
+}