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From: Stefan Berger <stefanb@linux.ibm.com>
To: keyrings@vger.kernel.org, linux-crypto@vger.kernel.org,
        herbert@gondor.apana.org.au, davem@davemloft.net
Cc: linux-kernel@vger.kernel.org, lukas@wunner.de, jarkko@kernel.org,
        Stefan Berger <stefanb@linux.ibm.com>
Subject: [PATCH] crypto: ecc - Protect ecc_digits_from_bytes from reading too many bytes
Date: Fri, 26 Apr 2024 18:55:53 -0400
Message-ID: <20240426225553.3038070-1-stefanb@linux.ibm.com>
Precedence: bulk
MIME-Version: 1.0
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Protect ecc_digits_from_bytes from reading too many bytes from the input
byte array in case an insufficient number of bytes is provided to fill the
output digit array of ndigits. Therefore, initialize the most significant
digits with 0 to avoid trying to read too many bytes later on.

If too many bytes are provided on the input byte array the extra bytes
are ignored since the input variable 'ndigits' limits the number of digits
that will be filled.

Fixes: d67c96fb97b5 ("crypto: ecdsa - Convert byte arrays with key coordinates to digits")
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 include/crypto/internal/ecc.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index 7ca1f463d1ec..56215f14ff96 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -67,9 +67,16 @@ static inline void ecc_swap_digits(const void *in, u64 *out, unsigned int ndigit
 static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
 					 u64 *out, unsigned int ndigits)
 {
+	int diff = ndigits - DIV_ROUND_UP(nbytes, sizeof(u64));
 	unsigned int o = nbytes & 7;
 	__be64 msd = 0;
 
+	/* diff > 0: not enough input bytes: set most significant digits to 0 */
+	while (diff > 0) {
+		out[--ndigits] = 0;
+		diff--;
+	}
+
 	if (o) {
 		memcpy((u8 *)&msd + sizeof(msd) - o, in, o);
 		out[--ndigits] = be64_to_cpu(msd);
-- 
2.43.0