crypto: ecdh - explicitly zeroize private_key

	private_key is overwritten with the key parameter passed in by the
	caller (if present), or alternatively a newly generated private key.
	However, it is possible that the caller provides a key (or the newly
	generated key) which is shorter than the previous key. In that
	scenario, some key material from the previous key would not be
	overwritten. The easiest solution is to explicitly zeroize the entire
	private_key array first.

	Note that this patch slightly changes the behavior of this function:
	previously, if the ecc_gen_privkey failed, the old private_key would
	remain. Now, the private_key is always zeroized. This behavior is
	consistent with the case where params.key is set and ecc_is_key_valid
	fails.

	Signed-off-by: Joachim Vandersmissen <git@jvdsn.com>
	Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Back-port of upstream commit: 73e5984

Signed-off-by: Jeremy Allison <jallison@ciq.com>

Author: jallisonciq

crypto/ecdh.c

@@ -54,6 +54,8 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 	ctx->curve_id = params.curve_id;
 	ctx->ndigits = ndigits;
 
+	memset(ctx->private_key, 0, sizeof(ctx->private_key));
+
 	if (!params.key || !params.key_size)
 		return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
 				       ctx->private_key);