From a1a4730c1f02cd85680cf7608ac81e0db59ee522 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemensik@redhat.com>
Date: Wed, 16 Jan 2019 16:27:33 +0100
Subject: [PATCH] Fix possible crash when loading corrupted file

Some values passes internal triggers by coincidence. Fix the check and
check also first_node_offset before even passing it further.
---
 lib/dns/rbt.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/lib/dns/rbt.c b/lib/dns/rbt.c
index ef6441b..404fd6d 100644
--- a/lib/dns/rbt.c
+++ b/lib/dns/rbt.c
@@ -754,7 +754,7 @@ treefix(dns_rbt_t *rbt, void *base, size_t filesize, dns_rbtnode_t *n,
 	}
 
 	CONFIRM((void *)n >= base);
-	CONFIRM((char *)n - (char *)base <= (int)nodemax);
+	CONFIRM((size_t)((char *)n - (char *)base) <= (int)nodemax);
 	CONFIRM(DNS_RBTNODE_VALID(n));
 
 	dns_name_init(&nodename, NULL);
@@ -911,7 +911,9 @@ dns_rbt_deserialize_tree(void *base_address, size_t filesize,
 	rbt->root = (dns_rbtnode_t *)((char *)base_address + header_offset +
 				      header->first_node_offset);
 
-	if ((header->nodecount * sizeof(dns_rbtnode_t)) > filesize) {
+	if ((header->nodecount * sizeof(dns_rbtnode_t)) > filesize
+	    || header->first_node_offset > filesize) {
+
 		result = ISC_R_INVALIDFILE;
 		goto cleanup;
 	}
-- 
2.21.1