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

1 files changed, 21 insertions, 11 deletions

diff --git a/sys/netinet/ip_input.c b/sys/netinet/ip_input.c
index 09f3f41..26cc060 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();
 }
 
 /*