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 <[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]>
zuai · Feb 12, 2016 · 613317b · 613317b
1 parent c05235d
commit 613317b
Showing 1 changed file with 2 additions and 1 deletion.
diff --git 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)
 			break;
-		rc = memcmp(xattr_data->digest, calc.digest,
+		rc = crypto_memneq(xattr_data->digest, calc.digest,
 			    sizeof(calc.digest));
 		if (rc)
 			rc = -EINVAL;