Close a race between hcb_insert() and hcb_delete()

Hit by:	dormando



git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4719 d4fa192b-c00b-0410-8231-f00ffab90ce4

bin/varnishd/hash_critbit.c

@@ -212,6 +212,12 @@ hcb_insert(struct hcb_root *root, struct objhead *oh, int has_lock)
 		pp = *p;
 	}
 
+	if (pp == 0) {
+		/* We raced hcb_delete and got a NULL pointer */
+		assert(!has_lock);
+		return (NULL);
+	}
+
 	assert(hcb_is_node(pp));
 
 	/* We found a node, does it match ? */