linux-kernel - [PATCH 10/23] KEYS: encrypted: use constant-time HMAC comparison

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Message-ID: <149692971287.11452.3700184292634708953.stgit@warthog.procyon.org.uk>
Date:   Thu, 08 Jun 2017 14:48:32 +0100
From:   David Howells <dhowells@...hat.com>
To:     jmorris@...ei.org
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        linux-security-module@...r.kernel.org, keyrings@...r.kernel.org,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>
Subject: [PATCH 10/23] KEYS: encrypted: use constant-time HMAC comparison

From: Eric Biggers <ebiggers@...gle.com>

MACs should, in general, be compared using crypto_memneq() to prevent
timing attacks.

Cc: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---

 security/keys/encrypted-keys/encrypted.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c
index 702c80662069..5c98c2fe03f0 100644
--- a/security/keys/encrypted-keys/encrypted.c
+++ b/security/keys/encrypted-keys/encrypted.c
@@ -30,6 +30,7 @@
 #include <linux/scatterlist.h>
 #include <linux/ctype.h>
 #include <crypto/aes.h>
+#include <crypto/algapi.h>
 #include <crypto/hash.h>
 #include <crypto/sha.h>
 #include <crypto/skcipher.h>
@@ -534,8 +535,8 @@ static int datablob_hmac_verify(struct encrypted_key_payload *epayload,
 	ret = calc_hmac(digest, derived_key, sizeof derived_key, p, len);
 	if (ret < 0)
 		goto out;
-	ret = memcmp(digest, epayload->format + epayload->datablob_len,
-		     sizeof digest);
+	ret = crypto_memneq(digest, epayload->format + epayload->datablob_len,
+			    sizeof(digest));
 	if (ret) {
 		ret = -EINVAL;
 		dump_hmac("datablob",