MFp4 @181628:

Free the rtentry after we diconnected it from the FIB and are counting
it as rttrash.  There might still be a chance we leak it from a different
code path but there is nothing we can do about this here.

Sponsored by:	ISPsystem (in February)
Reviewed by:	julian (in February)
MFC after:	2 weeks

sys/netinet/in_rmx.c

@@ -408,14 +408,28 @@ in_ifadownkill(struct radix_node *rn, void *xap)
 	if (rt->rt_ifa == ap->ifa &&
 	    (ap->del || !(rt->rt_flags & RTF_STATIC))) {
 		/*
-		 * We need to disable the automatic prune that happens
-		 * in this case in rtrequest() because it will blow
-		 * away the pointers that rn_walktree() needs in order
-		 * continue our descent.  We will end up deleting all
-		 * the routes that rtrequest() would have in any case,
-		 * so that behavior is not needed there.
+		 * Aquire a reference so that it can later be freed
+		 * as the refcount would be 0 here in case of at least
+		 * ap->del.
+		 */
+		RT_ADDREF(rt);
+		/*
+		 * Disconnect it from the tree and permit protocols
+		 * to cleanup.
 		 */
 		rtexpunge(rt);
+		/*
+		 * At this point it is an rttrash node, and in case
+		 * the above is the only reference we must free it.
+		 * If we do not noone will have a pointer and the
+		 * rtentry will be leaked forever.
+		 * In case someone else holds a reference, we are
+		 * fine as we only decrement the refcount. In that
+		 * case if the other entity calls RT_REMREF, we
+		 * will still be leaking but at least we tried.
+		 */
+		RTFREE_LOCKED(rt);
+		return (0);
 	}
 	RT_UNLOCK(rt);
 	return 0;