crypto: ecdsa - Use ecc_digits_from_bytes to create hash digits array

Since ecc_digits_from_bytes will provide zeros when an insufficient number
of bytes are passed in the input byte array, use it to create the hash
digits directly from the input byte array. This avoids going through an
intermediate byte array (rawhash) that has the first few bytes filled with
zeros.
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/ecdsa.c

@@ -142,10 +142,8 @@ static int ecdsa_verify(struct akcipher_request *req)
 	struct ecdsa_signature_ctx sig_ctx = {
 		.curve = ctx->curve,
 	};
-	u8 rawhash[ECC_MAX_BYTES];
 	u64 hash[ECC_MAX_DIGITS];
 	unsigned char *buffer;
-	ssize_t diff;
 	int ret;
 
 	if (unlikely(!ctx->pub_key_set))
@@ -164,18 +162,11 @@ static int ecdsa_verify(struct akcipher_request *req)
 	if (ret < 0)
 		goto error;
 
-	/* if the hash is shorter then we will add leading zeros to fit to ndigits */
-	diff = bufsize - req->dst_len;
-	if (diff >= 0) {
-		if (diff)
-			memset(rawhash, 0, diff);
-		memcpy(&rawhash[diff], buffer + req->src_len, req->dst_len);
-	} else if (diff < 0) {
-		/* given hash is longer, we take the left-most bytes */
-		memcpy(&rawhash, buffer + req->src_len, bufsize);
-	}
+	if (bufsize > req->dst_len)
+		bufsize = req->dst_len;
 
-	ecc_swap_digits((u64 *)rawhash, hash, ctx->curve->g.ndigits);
+	ecc_digits_from_bytes(buffer + req->src_len, bufsize,
+			      hash, ctx->curve->g.ndigits);
 
 	ret = _ecdsa_verify(ctx, hash, sig_ctx.r, sig_ctx.s);