Re: [PATCH v2 6/7] fs: use HKDF implementation from kernel crypto API

Eric Biggers
2021-01-28T20:20:01Z

On Sun, Jan 24, 2021 at 03:04:31PM +0100, Stephan Müller wrote:
> @@ -74,16 +57,14 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> return PTR_ERR(hmac_tfm);
> }
>
> - if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != sizeof(prk))) {
> + if (WARN_ON(crypto_shash_digestsize(hmac_tfm) != HKDF_HASHLEN)) {
> err = -EINVAL;
> goto err_free_tfm;
> }
>
> - err = hkdf_extract(hmac_tfm, master_key, master_key_size, prk);
> - if (err)
> - goto err_free_tfm;
> -
> - err = crypto_shash_setkey(hmac_tfm, prk, sizeof(prk));
> + /* HKDF-Extract (RFC 5869 section 2.2), unsalted */
> + err = crypto_hkdf_extract(hmac_tfm, NULL, 0,
> + master_key, master_key_size);
> if (err)
> goto err_free_tfm;
>
> @@ -93,7 +74,6 @@ int fscrypt_init_hkdf(struct fscrypt_hkdf *hkdf, const u8 *master_key,
> err_free_tfm:
> crypto_free_shash(hmac_tfm);
> out:
> - memzero_explicit(prk, sizeof(prk));
> return err;
> }

The 'out' label isn't needed anymore. 'goto out' should be replaced with
'return 0'.

- Eric