dnsmasq/backport-dnsmasq-2.77-underflow.patch

From 4d3ef152a5d0a3cf053d41ea950823bfcc0ea5c2 Mon Sep 17 00:00:00 2001
From: xiaoweiwei <xiaoweiwei5@huawei.com>
Date: Tue, 28 Jul 2020 10:32:50 +0800
Subject: [PATCH] underflow

---
 src/rfc1035.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/rfc1035.c b/src/rfc1035.c
index fefe63d..d3cce6f 100644
--- a/src/rfc1035.c
+++ b/src/rfc1035.c
@@ -1340,6 +1340,9 @@ size_t answer_request(struct dns_header *header, char *limit, size_t qlen,
   size_t len;
   int rd_bit = (header->hb3 & HB3_RD);
 
+  // Make sure we do not underflow here too
+  if (qlen > (limit - ((char *)header))) return 0;
+
   /* never answer queries with RD unset, to avoid cache snooping. */
   if (ntohs(header->ancount) != 0 ||
       ntohs(header->nscount) != 0 ||
-- 
1.8.3.1