From: Ryan Ware <ware@linux.intel.com>
Date: Thu, 11 Feb 2016 23:58:44 +0000 (-0800)
Subject: EVM: Use crypto_memneq() for digest comparisons
X-Git-Tag: v3.18.28~15
X-Git-Url: http://git.hungrycats.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6702fc0c98d40442f9e74e10c499d68cd96455df;p=linux

EVM: Use crypto_memneq() for digest comparisons

[ Upstream commit 613317bd212c585c20796c10afe5daaa95d4b0a1 ]

This patch fixes vulnerability CVE-2016-2085.  The problem exists
because the vm_verify_hmac() function includes a use of memcmp().
Unfortunately, this allows timing side channel attacks; specifically
a MAC forgery complexity drop from 2^128 to 2^12.  This patch changes
the memcmp() to the cryptographically safe crypto_memneq().

Reported-by: Xiaofei Rex Guo <xiaofei.rex.guo@intel.com>
Signed-off-by: Ryan Ware <ware@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
---

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 4ada1a97a60b..e1998df4c160 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -24,6 +24,7 @@
 #include <linux/evm.h>
 #include <linux/magic.h>
 #include <crypto/hash.h>
+#include <crypto/algapi.h>
 #include "evm.h"
 
 int evm_initialized;
@@ -149,7 +150,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
 				   xattr_value_len, calc.digest);
 		if (rc)
 			break;
-		rc = memcmp(xattr_data->digest, calc.digest,
+		rc = crypto_memneq(xattr_data->digest, calc.digest,
 			    sizeof(calc.digest));
 		if (rc)
 			rc = -EINVAL;