From ad675846656a35d02c1d2e150d979fc06c18511f Mon Sep 17 00:00:00 2001
From: Sam Leffler <sam@FreeBSD.org>
Date: Fri, 7 Nov 2003 01:47:52 +0000
Subject: [PATCH] Fix locking of the ip forwarding cache.  We were holding a
 reference to a routing table entry w/o bumping the reference count or locking
 against the entry being free'd.  This caused major havoc (for some reason it
 appeared most frequently for folks running natd).  Fix is to bump the
 reference count whenever we copy the route cache contents into a private copy
 so the entry cannot be reclaimed out from under us.  This is a short term fix
 as the forthcoming routing table changes will eliminate this cache entirely.

Supported by:	FreeBSD Foundation
---
 sys/netinet/ip_input.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/sys/netinet/ip_input.c b/sys/netinet/ip_input.c
index 09f3f41371e5..26cc060efa09 100644
--- a/sys/netinet/ip_input.c
+++ b/sys/netinet/ip_input.c
@@ -213,7 +213,9 @@ int fw_one_pass = 1;
 ip_dn_io_t *ip_dn_io_ptr;
 
 /*
- * One deep route cache for ip forwarding.
+ * One deep route cache for ip forwarding.  This is done
+ * very inefficiently.  We don't care as it's about to be
+ * replaced by something better.
  */
 static struct rtcache {
 	struct route	rc_ro;		/* most recently used route */
@@ -223,28 +225,37 @@ static struct rtcache {
 #define	RTCACHE_LOCK()		mtx_lock(&ip_fwdcache.rc_mtx)
 #define	RTCACHE_UNLOCK()	mtx_unlock(&ip_fwdcache.rc_mtx)
 #define	RTCACHE_LOCK_INIT() \
-	mtx_init(&ip_fwdcache.rc_mtx, "route cache", NULL, MTX_DEF);
+	mtx_init(&ip_fwdcache.rc_mtx, "route cache", NULL, MTX_DEF)
 #define	RTCACHE_LOCK_ASSERT()	mtx_assert(&ip_fwdcache.rc_mtx, MA_OWNED)
 
 /*
- * Get the current route cache contents.
+ * Get a copy of the current route cache contents.
  */
 #define	RTCACHE_GET(_ro) do {					\
+	struct rtentry *rt;					\
 	RTCACHE_LOCK();						\
 	*(_ro) = ip_fwdcache.rc_ro;				\
+	if ((rt = (_ro)->ro_rt) != NULL) {			\
+		RT_LOCK(rt);					\
+		rt->rt_refcnt++;				\
+		RT_UNLOCK(rt);					\
+	}							\
 	RTCACHE_UNLOCK();					\
 } while (0)
 
 /*
- * Update the cache contents.  We optimize this using
- * the routing table reference. XXX is this safe?
+ * Update the cache contents.
  */
 #define	RTCACHE_UPDATE(_ro) do {				\
-	if ((_ro)->ro_rt != ip_fwdcache.rc_ro.ro_rt) {		\
-		RTCACHE_LOCK();					\
+	struct rtentry *rt;					\
+	RTCACHE_LOCK();						\
+	rt = ip_fwdcache.rc_ro.ro_rt;				\
+	if ((_ro)->ro_rt != rt) {				\
 		ip_fwdcache.rc_ro = *(_ro);			\
-		RTCACHE_UNLOCK();				\
+		if (rt)						\
+			RTFREE(rt);				\
 	}							\
+	RTCACHE_UNLOCK();					\
 } while (0)
 
 /*
@@ -332,15 +343,14 @@ ip_init()
 void
 ip_forward_cacheinval(void)
 {
-	struct rtentry *rt = NULL;
+	struct rtentry *rt;
 
 	RTCACHE_LOCK();
 	rt = ip_fwdcache.rc_ro.ro_rt;
 	ip_fwdcache.rc_ro.ro_rt = 0;
-	RTCACHE_UNLOCK();
-
 	if (rt != NULL)
 		RTFREE(rt);
+	RTCACHE_UNLOCK();
 }
 
 /*