1 files changed, 317 insertions, 0 deletions
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
new file mode 100644
index 000000000..adf6dc8a9
--- /dev/null
+++ b/net/ipv4/inetpeer.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *		INETPEER - A storage for permanent information about peers
+ *
+ *  Authors:	Andrey V. Savochkin <saw@msu.ru>
+ */
+
+#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>
+#include <linux/siphash.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;
+static siphash_aligned_key_t inetpeer_hash_key __read_mostly;
+
+static u64 inetpeer_addr_hash(const struct inetpeer_addr *a)
+{
+	net_get_random_once(&inetpeer_hash_key, sizeof(inetpeer_hash_key));
+
+	if (a->family == AF_INET)
+		return siphash_2u32((__force u32)a->a4.addr, a->a4.vif,
+				    &inetpeer_hash_key);
+
+	return siphash_4u32((__force u32)a->a6.s6_addr32[0],
+			    (__force u32)a->a6.s6_addr32[1],
+			    (__force u32)a->a6.s6_addr32[2],
+			    (__force u32)a->a6.s6_addr32[3],
+			    &inetpeer_hash_key);
+}
+
+static int inetpeer_entry_cmp(u64 dhash,
+			      const struct inetpeer_addr *daddr,
+			      const struct inet_peer *p)
+{
+	if (dhash < p->hash)
+		return -1;
+	if (dhash > p->hash)
+		return 1;
+
+	return inetpeer_addr_cmp(daddr, &p->daddr);
+}
+
+void inet_peer_base_init(struct inet_peer_base *bp)
+{
+	bp->rb_root = RB_ROOT;
+	seqlock_init(&bp->lock);
+	bp->total = 0;
+}
+
+#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,
+				u64 dhash,
+				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;
+	u32 now;
+
+	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_entry_cmp(dhash, daddr, p);
+		if (cmp == 0) {
+			now = jiffies;
+			if (READ_ONCE(p->dtime) != now)
+				WRITE_ONCE(p->dtime, now);
+			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;
+}
+
+/* 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];
+
+		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--;
+			kfree_rcu(p, rcu);
+		}
+	}
+}
+
+/* Must be called under RCU : No refcount change is done here. */
+struct inet_peer *inet_getpeer(struct inet_peer_base *base,
+			       const struct inetpeer_addr *daddr)
+{
+	struct inet_peer *p, *gc_stack[PEER_MAX_GC];
+	u64 dhash = inetpeer_addr_hash(daddr);
+	struct rb_node **pp, *parent;
+	unsigned int gc_cnt, seq;
+
+	/* Attempt a lockless lookup first.
+	 * Because of a concurrent writer, we might not find an existing entry.
+	 */
+	seq = read_seqbegin(&base->lock);
+	p = lookup(daddr, dhash, base, seq, NULL, &gc_cnt, &parent, &pp);
+
+	/* Make sure tree was not modified during our lookup. */
+	if (p && !read_seqretry(&base->lock, seq))
+		return p;
+
+	/* 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, dhash, base, seq, gc_stack, &gc_cnt, &parent, &pp);
+	if (!p) {
+		p = kmem_cache_alloc(peer_cachep, GFP_ATOMIC);
+		if (p) {
+			p->daddr = *daddr;
+			p->hash = dhash;
+			p->dtime = (__u32)jiffies;
+			refcount_set(&p->refcnt, 1);
+			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;
+}
+
+void inet_putpeer(struct inet_peer *p)
+{
+	if (refcount_dec_and_test(&p->refcnt))
+		kfree_rcu(p, rcu);
+}
+
+/*
+ *	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, otoken, delta;
+	bool rc = false;
+
+	if (!peer)
+		return true;
+
+	token = otoken = READ_ONCE(peer->rate_tokens);
+	now = jiffies;
+	delta = now - READ_ONCE(peer->rate_last);
+	if (delta) {
+		WRITE_ONCE(peer->rate_last, now);
+		token += delta;
+		if (token > XRLIM_BURST_FACTOR * timeout)
+			token = XRLIM_BURST_FACTOR * timeout;
+	}
+	if (token >= timeout) {
+		token -= timeout;
+		rc = true;
+	}
+	if (token != otoken)
+		WRITE_ONCE(peer->rate_tokens, token);
+	return rc;
+}
+
+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;
+}