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>
diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index f716025..e6ea9d4 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 @@
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;
