From d2a286714f136404d05c8981a2e0820c1dd6e0a9 Mon Sep 17 00:00:00 2001

From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>

Date: Sun, 18 Jun 2017 16:07:57 -0400

Subject: [PATCH 2/2] resolved: simplify alloc size calculation

The allocation size was calculated in a complicated way, and for values

close to the page size we would actually allocate less than requested.

Reported by Chris Coulson <chris.coulson@canonical.com>.

CVE-2017-9445

---

 src/resolve/resolved-dns-packet.c | 8 +-------

 src/resolve/resolved-dns-packet.h | 2 --

 2 files changed, 1 insertion(+), 9 deletions(-)

diff --git a/src/resolve/resolved-dns-packet.c b/src/resolve/resolved-dns-packet.c

index 240ee448f4..821b66e266 100644

--- a/src/resolve/resolved-dns-packet.c

+++ b/src/resolve/resolved-dns-packet.c

@@ -47,13 +47,7 @@ int dns_packet_new(DnsPacket **ret, DnsProtocol protocol, size_t mtu) {

         assert(ret);

-        if (mtu <= UDP_PACKET_HEADER_SIZE)

-                a = DNS_PACKET_SIZE_START;

-        else

-                a = mtu - UDP_PACKET_HEADER_SIZE;

-

-        if (a < DNS_PACKET_HEADER_SIZE)

-                a = DNS_PACKET_HEADER_SIZE;

+        a = MAX(mtu, DNS_PACKET_HEADER_SIZE);

         /* round up to next page size */

         a = PAGE_ALIGN(ALIGN(sizeof(DnsPacket)) + a) - ALIGN(sizeof(DnsPacket));

diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h

index 2c92392e4d..3abcaf8cf3 100644

--- a/src/resolve/resolved-dns-packet.h

+++ b/src/resolve/resolved-dns-packet.h

@@ -66,8 +66,6 @@ struct DnsPacketHeader {

 /* With EDNS0 we can use larger packets, default to 4096, which is what is commonly used */

 #define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 4096

-#define DNS_PACKET_SIZE_START 512

-

 struct DnsPacket {

         int n_ref;

         DnsProtocol protocol;

-- 

2.13.0