Commit 50e2fe0e authored by Ryan Ware's avatar Ryan Ware Committed by Luis Henriques

EVM: Use crypto_memneq() for digest comparisons

commit 613317bd 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: default avatarXiaofei Rex Guo <xiaofei.rex.guo@intel.com>
Signed-off-by: default avatarRyan Ware <ware@linux.intel.com>
Signed-off-by: default avatarMimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: default avatarJames Morris <james.l.morris@oracle.com>
Cc: Moritz Muehlenhoff <jmm@inutil.org>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent f95bf9a8
...@@ -24,6 +24,7 @@ ...@@ -24,6 +24,7 @@
#include <linux/evm.h> #include <linux/evm.h>
#include <linux/magic.h> #include <linux/magic.h>
#include <crypto/hash.h> #include <crypto/hash.h>
#include <crypto/algapi.h>
#include "evm.h" #include "evm.h"
int evm_initialized; int evm_initialized;
...@@ -148,7 +149,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry, ...@@ -148,7 +149,7 @@ static enum integrity_status evm_verify_hmac(struct dentry *dentry,
xattr_value_len, calc.digest); xattr_value_len, calc.digest);
if (rc) if (rc)
break; break;
rc = memcmp(xattr_data->digest, calc.digest, rc = crypto_memneq(xattr_data->digest, calc.digest,
sizeof(calc.digest)); sizeof(calc.digest));
if (rc) if (rc)
rc = -EINVAL; rc = -EINVAL;
......
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