[PATCH 3.19.y-ckt 005/196] EVM: Use crypto_memneq() for digest comparisons

From: Kamal Mostafa
Date: Tue Mar 08 2016 - 20:20:58 EST

3.19.8-ckt16 -stable review patch. If anyone has any objections, please let me know.


From: Ryan Ware <ware@xxxxxxxxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Ryan Ware <ware@xxxxxxxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
Signed-off-by: James Morris <james.l.morris@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
security/integrity/evm/evm_main.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/integrity/evm/evm_main.c b/security/integrity/evm/evm_main.c
index 02c6e4d..6c9c11d 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)
- rc = memcmp(xattr_data->digest, calc.digest,
+ rc = crypto_memneq(xattr_data->digest, calc.digest,
if (rc)
rc = -EINVAL;