linux-kernel - [PATCH] crypto: ecc - Fix off-by-one missing to clear most significant digit

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Message-ID: <20240613213820.995832-1-stefanb@linux.ibm.com>
Date: Thu, 13 Jun 2024 17:38:20 -0400
From: Stefan Berger <stefanb@...ux.ibm.com>
To: keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        herbert@...dor.apana.org.au, davem@...emloft.net
Cc: linux-kernel@...r.kernel.org, jarkko@...nel.org,
        Stefan Berger <stefanb@...ux.ibm.com>,
        Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
Subject: [PATCH] crypto: ecc - Fix off-by-one missing to clear most significant digit

Fix an off-by-one error where the most significant digit was not
initialized leading to signature verification failures by the testmgr.

Example: If a curve requires ndigits (=9) and diff (=2) indicates that
2 digits need to be set to zero then start with digit 'ndigits - diff' (=7)
and clear 'diff' digits starting from there, so 7 and 8.

Reported-by: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
Closes: https://lore.kernel.org/linux-crypto/619bc2de-b18a-4939-a652-9ca886bf6349@linux.ibm.com/T/#m045d8812409ce233c17fcdb8b88b6629c671f9f4
Fixes: 2fd2a82ccbfc ("crypto: ecdsa - Use ecc_digits_from_bytes to create hash digits array")
Signed-off-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 crypto/ecc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/ecc.c b/crypto/ecc.c
index fe761256e335..dd48d9928a21 100644
--- a/crypto/ecc.c
+++ b/crypto/ecc.c
@@ -78,7 +78,7 @@ void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
 	/* diff > 0: not enough input bytes: set most significant digits to 0 */
 	if (diff > 0) {
 		ndigits -= diff;
-		memset(&out[ndigits - 1], 0, diff * sizeof(u64));
+		memset(&out[ndigits], 0, diff * sizeof(u64));
 	}
 
 	if (o) {
-- 
2.44.0