From d05d116da39c0a5c580ceaac6ba069899b82c5a0 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 | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/dns/rbt.c b/lib/dns/rbt.c
index 5aee5f6..7f2c2d2 100644
--- a/lib/dns/rbt.c
+++ b/lib/dns/rbt.c
@@ -945,7 +945,9 @@ 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;
 	}
-- 
2.31.1