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: firefly_0821_release~3391^2~16
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=8592536bcfcbc717a3bf7cec57d7c1b38f4eec1d;p=firefly-linux-kernel-4.4.55.git

EVM: Use crypto_memneq() for digest comparisons

commit 613317bd212c585c20796c10afe5daaa95d4b0a1 upstream.

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>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 1334e02ae8f4..3d145a3ffccf 100644
--- a/security/integrity/evm/evm_main.c
+++ b/security/integrity/evm/evm_main.c
@@ -23,6 +23,7 @@
 #include <linux/integrity.h>
 #include <linux/evm.h>
 #include <crypto/hash.h>
+#include <crypto/algapi.h>
 #include "evm.h"
 
 int evm_initialized;
@@ -148,7 +149,7 @@ 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;