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EVM: Use crypto_memneq() for digest comparisons

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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 <[email protected]>
Signed-off-by: Ryan Ware <[email protected]>
Cc: [email protected]
Signed-off-by: Mimi Zohar <[email protected]>
Signed-off-by: James Morris <[email protected]>
This commit is contained in:
Ryan Ware 2016-02-11 15:58:44 -08:00 • committed by James Morris
commit 613317bd21
1 changed files with 2 additions and 1 deletions
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3
security/integrity/evm/evm_main.c
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@ -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;