[COMMITTED] Fix CVE-2015-1781: buffer overflow in nss_dns [BZ#18287]

From 2959eda9272a033863c271aff62095abd01bd4e3 Mon Sep 17 00:00:00 2001
From: Arjun Shankar <arjun.is@lostca.se>
Date: Tue, 21 Apr 2015 14:06:31 +0200
Subject: [PATCH] CVE-2015-1781: resolv/nss_dns/dns-host.c buffer overflow
 [BZ#18287]

---
 ChangeLog                 | 6 ++++++
 NEWS                      | 9 ++++++++-
 resolv/nss_dns/dns-host.c | 3 ++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 7c3e625..26dcfc7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@ 
+2015-04-21  Arjun Shankar  <arjun.is@lostca.se>
+
+	[BZ #18287]
+	* resolv/nss_dns/dns-host.c (getanswer_r): Adjust buffer length
+	based on padding.  (CVE-2015-1781)
+
 2015-04-20  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
 	* nptl/pthread_cond_timedwait.c: Change include bits/libc-vdso.h to just
diff --git a/NEWS b/NEWS
index 2bbd6a3..ccc4d13 100644
--- a/NEWS
+++ b/NEWS
@@ -16,7 +16,14 @@  Version 2.22
   17969, 17978, 17987, 17991, 17996, 17998, 17999, 18019, 18020, 18029,
   18030, 18032, 18036, 18038, 18039, 18042, 18043, 18046, 18047, 18068,
   18080, 18093, 18100, 18104, 18110, 18111, 18128, 18138, 18185, 18197,
-  18206, 18210, 18211, 18247.
+  18206, 18210, 18211, 18247, 18287.
+
+* A buffer overflow in gethostbyname_r and related functions performing DNS
+  requests has been fixed.  If the NSS functions were called with a
+  misaligned buffer, the buffer length change due to pointer alignment was
+  not taken into account.  This could result in application crashes or,
+  potentially arbitrary code execution, using crafted, but syntactically
+  valid DNS responses.  (CVE-2015-1781)
 
 * A powerpc and powerpc64 optimization for TLS, similar to TLS descriptors
   for LD and GD on x86 and x86-64, has been implemented.  You will need
diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index b16b0dd..d8c5579 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -615,7 +615,8 @@  getanswer_r (const querybuf *answer, int anslen, const char *qname, int qtype,
   int have_to_map = 0;
   uintptr_t pad = -(uintptr_t) buffer % __alignof__ (struct host_data);
   buffer += pad;
-  if (__glibc_unlikely (buflen < sizeof (struct host_data) + pad))
+  buflen = buflen > pad ? buflen - pad : 0;
+  if (__glibc_unlikely (buflen < sizeof (struct host_data)))
     {
       /* The buffer is too small.  */
     too_small:
-- 
2.1.0