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From 897c113fda0886a28a986cc6ba17bb93bd6cb1c7 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Mon, 25 Sep 2017 20:11:58 +0100
Subject: [PATCH] Security fix, CVE-2017-14496, Integer underflow in DNS
response creation.
Fix DoS in DNS. Invalid boundary checks in the
add_pseudoheader function allows a memcpy call with negative
size An attacker which can send malicious DNS queries
to dnsmasq can trigger a DoS remotely.
dnsmasq is vulnerable only if one of the following option is
specified: --add-mac, --add-cpe-id or --add-subnet.
CVE: CVE-2017-14496
Upstream-Status: Backport
Signed-off-by: Sona Sarmadi <sona.sarmadi@enea.com>
---
CHANGELOG | 11 +++++++++++
src/edns0.c | 13 ++++++++++++-
2 files changed, 23 insertions(+), 1 deletion(-)
diff --git a/CHANGELOG b/CHANGELOG
index d1cc074..8fe00ed 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -60,6 +60,17 @@ version 2.78
and Kevin Hamacher of the Google Security Team for
finding this.
+ Fix DoS in DNS. Invalid boundary checks in the
+ add_pseudoheader function allows a memcpy call with negative
+ size An attacker which can send malicious DNS queries
+ to dnsmasq can trigger a DoS remotely.
+ dnsmasq is vulnerable only if one of the following option is
+ specified: --add-mac, --add-cpe-id or --add-subnet.
+ CVE-2017-14496 applies.
+ Credit to Felix Wilhelm, Fermin J. Serna, Gabriel Campana
+ and Kevin Hamacher of the Google Security Team for
+ finding this.
+
version 2.77
Generate an error when configured with a CNAME loop,
diff --git a/src/edns0.c b/src/edns0.c
index f5b798c..95b74ee 100644
--- a/src/edns0.c
+++ b/src/edns0.c
@@ -144,7 +144,7 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
GETSHORT(len, p);
/* malformed option, delete the whole OPT RR and start again. */
- if (i + len > rdlen)
+ if (i + 4 + len > rdlen)
{
rdlen = 0;
is_last = 0;
@@ -193,6 +193,8 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
ntohs(header->ancount) + ntohs(header->nscount) + ntohs(header->arcount),
header, plen)))
return plen;
+ if (p + 11 > limit)
+ return plen; /* Too big */
*p++ = 0; /* empty name */
PUTSHORT(T_OPT, p);
PUTSHORT(udp_sz, p); /* max packet length, 512 if not given in EDNS0 header */
@@ -204,6 +206,11 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
/* Copy back any options */
if (buff)
{
+ if (p + rdlen > limit)
+ {
+ free(buff);
+ return plen; /* Too big */
+ }
memcpy(p, buff, rdlen);
free(buff);
p += rdlen;
@@ -220,8 +227,12 @@ size_t add_pseudoheader(struct dns_header *header, size_t plen, unsigned char *l
/* Add new option */
if (optno != 0 && replace != 2)
{
+ if (p + 4 > limit)
+ return plen; /* Too big */
PUTSHORT(optno, p);
PUTSHORT(optlen, p);
+ if (p + optlen > limit)
+ return plen; /* Too big */
memcpy(p, opt, optlen);
p += optlen;
PUTSHORT(p - datap, lenp);
--
1.7.10.4
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