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From:   Daniele Alessandrelli <daniele.alessandrelli@linux.intel.com>
To:     herbert@gondor.apana.org.au
Cc:     daniele.alessandrelli@intel.com, linux-crypto@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH] crypto: keembay-ocs-aes - Fix 'q' assignment during CCM B0 generation
Date:   Wed,  3 Feb 2021 15:42:10 +0000
Message-Id: <20210203154210.246667-1-daniele.alessandrelli@linux.intel.com>
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From: Daniele Alessandrelli <daniele.alessandrelli@intel.com>

In ocs_aes_ccm_write_b0(), 'q' (the octet length of the binary
representation of the octet length of the payload) is set to 'iv[0]',
while it should be set to 'iv[0] & 0x7' (i.e., only the last 3
bits of iv[0] should be used), as documented in NIST Special Publication
800-38C:
https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38c.pdf

In practice, this is not an issue, since 'iv[0]' is checked to be in the
range [1-7] by ocs_aes_validate_inputs(), but let's fix the assignment
anyway, in order to make the code more robust.

Signed-off-by: Daniele Alessandrelli <daniele.alessandrelli@intel.com>
---
 drivers/crypto/keembay/ocs-aes.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/crypto/keembay/ocs-aes.c b/drivers/crypto/keembay/ocs-aes.c
index b85c89477afa..be9f32fc8f42 100644
--- a/drivers/crypto/keembay/ocs-aes.c
+++ b/drivers/crypto/keembay/ocs-aes.c
@@ -1080,15 +1080,15 @@ static int ocs_aes_ccm_write_b0(const struct ocs_aes_dev *aes_dev,
 	/*
 	 * q is the octet length of Q.
 	 * q can only be an element of {2, 3, 4, 5, 6, 7, 8} and is encoded as
-	 * q - 1 == iv[0]
+	 * q - 1 == iv[0] & 0x7;
 	 */
 	b0[0] |= iv[0] & 0x7;
 	/*
 	 * Copy the Nonce N from IV to B0; N is located in iv[1]..iv[15 - q]
 	 * and must be copied to b0[1]..b0[15-q].
-	 * q == iv[0] + 1
+	 * q == (iv[0] & 0x7) + 1
 	 */
-	q = iv[0] + 1;
+	q = (iv[0] & 0x7) + 1;
 	for (i = 1; i <= 15 - q; i++)
 		b0[i] = iv[i];
 	/*
-- 
2.26.2