Commit 613317bd authored Feb 11, 2016 by Ryan Ware Committed by James Morris Feb 12, 2016

EVM: Use crypto_memneq() for digest comparisons



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>

parent c05235d5

security/integrity/evm/evm_main.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -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;