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@linux.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@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/ecc.c b/crypto/ecc.c
index af698f8852fbb16674b5d1f340f8950dfbfa2e80..420decdad7d94f40bdf4bdf60862c957c810496e 100644 (file)
--- 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) {