crypto: ecdh - explicitly zeroize private_key

From: Joachim Vandersmissen <[email protected]>

commit 73e5984e540a76a2ee1868b91590c922da8c24c9 upstream.

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.

---
Backport fix for CVE-2024-42098

 crypto/ecdh.c | 2 ++
 1 file changed, 2 insertions(+)

index b6f493e82812..c37e8d35387d 100644
@@ -33,6 +33,8 @@ static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
 	    params.key_size > sizeof(u64) * ctx->ndigits)
 		return -EINVAL;
 
+	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);

2.53.0