Re: [Qemu-devel] [PATCH v2 09/13] qcrypto-block: extract check and parse header

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Aug 26, 2019 at 04:50:59PM +0300, Maxim Levitsky wrote:
> This is just to make qcrypto_block_luks_open more
> reasonable in size.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  crypto/block-luks.c | 254 +++++++++++++++++++++++++-------------------
>  1 file changed, 146 insertions(+), 108 deletions(-)
> 
> diff --git a/crypto/block-luks.c b/crypto/block-luks.c
> index b4dc6fc899..cc9a52c9af 100644
> --- a/crypto/block-luks.c
> +++ b/crypto/block-luks.c
> @@ -508,6 +508,148 @@ fail:
>      return ret;
>  }
>  
> +/*
> + * Does basic sanity checks on the LUKS header
> + */
> +static int
> +qcrypto_block_luks_check_header(const QCryptoBlockLUKS *luks, Error **errp)
> +{
> +    int ret;
> +
> +    if (memcmp(luks->header.magic, qcrypto_block_luks_magic,
> +               QCRYPTO_BLOCK_LUKS_MAGIC_LEN) != 0) {
> +        error_setg(errp, "Volume is not in LUKS format");
> +        ret = -EINVAL;
> +        goto fail;
> +    }

Just 'return -1' here immediately - don't return an errno, as we're
using Error objects for reporting.

> +
> +    if (luks->header.version != QCRYPTO_BLOCK_LUKS_VERSION) {
> +        error_setg(errp, "LUKS version %" PRIu32 " is not supported",
> +                   luks->header.version);
> +        ret = -ENOTSUP;
> +        goto fail;
> +    }
> +
> +    return 0;
> +fail:
> +    return ret;
> +}
> +
> +/*
> + * Parses the crypto parameters that are stored in the LUKS header
> + */
> +
> +static int
> +qcrypto_block_luks_parse_header(QCryptoBlockLUKS *luks, Error **errp)
> +{
> +    g_autofree char *cipher_mode = g_strdup(luks->header.cipher_mode);
> +    char *ivgen_name, *ivhash_name;
> +    int ret = -1;
> +    Error *local_err = NULL;
> +
> +    /*
> +     * The cipher_mode header contains a string that we have
> +     * to further parse, of the format
> +     *
> +     *    <cipher-mode>-<iv-generator>[:<iv-hash>]
> +     *
> +     * eg  cbc-essiv:sha256, cbc-plain64
> +     */
> +    ivgen_name = strchr(cipher_mode, '-');
> +    if (!ivgen_name) {
> +        ret = -EINVAL;

Again, don't use errnos - just return -1 in this method.

> +        error_setg(errp, "Unexpected cipher mode string format %s",
> +                   luks->header.cipher_mode);
> +        goto out;
> +    }
> +    *ivgen_name = '\0';
> +    ivgen_name++;
> +
> +    ivhash_name = strchr(ivgen_name, ':');
> +    if (!ivhash_name) {
> +        luks->ivgen_hash_alg = 0;
> +    } else {
> +        *ivhash_name = '\0';
> +        ivhash_name++;
> +
> +        luks->ivgen_hash_alg = qcrypto_block_luks_hash_name_lookup(ivhash_name,
> +                                                                   &local_err);
> +        if (local_err) {
> +            ret = -ENOTSUP;
> +            error_propagate(errp, local_err);
> +            goto out;
> +        }
> +    }
> +
> +    luks->cipher_mode = qcrypto_block_luks_cipher_mode_lookup(cipher_mode,
> +                                                              &local_err);
> +    if (local_err) {
> +        ret = -ENOTSUP;
> +        error_propagate(errp, local_err);
> +        goto out;
> +    }
> +
> +    luks->cipher_alg =
> +            qcrypto_block_luks_cipher_name_lookup(luks->header.cipher_name,
> +                                                  luks->cipher_mode,
> +                                                  luks->header.master_key_len,
> +                                                  &local_err);
> +    if (local_err) {
> +        ret = -ENOTSUP;
> +        error_propagate(errp, local_err);
> +        goto out;
> +    }
> +
> +    luks->hash_alg =
> +            qcrypto_block_luks_hash_name_lookup(luks->header.hash_spec,
> +                                               &local_err);
> +    if (local_err) {
> +        ret = -ENOTSUP;
> +        error_propagate(errp, local_err);
> +        goto out;
> +    }
> +
> +    luks->ivgen_alg = qcrypto_block_luks_ivgen_name_lookup(ivgen_name,
> +                                                           &local_err);
> +    if (local_err) {
> +        ret = -ENOTSUP;
> +        error_propagate(errp, local_err);
> +        goto out;
> +    }
> +
> +    if (luks->ivgen_alg == QCRYPTO_IVGEN_ALG_ESSIV) {
> +        if (!ivhash_name) {
> +            ret = -EINVAL;
> +            error_setg(errp, "Missing IV generator hash specification");
> +            goto out;
> +        }
> +        luks->ivgen_cipher_alg =
> +                qcrypto_block_luks_essiv_cipher(luks->cipher_alg,
> +                                                luks->ivgen_hash_alg,
> +                                                &local_err);
> +        if (local_err) {
> +            ret = -ENOTSUP;
> +            error_propagate(errp, local_err);
> +            goto out;
> +        }
> +    } else {
> +
> +        /*
> +         * Note we parsed the ivhash_name earlier in the cipher_mode
> +         * spec string even with plain/plain64 ivgens, but we
> +         * will ignore it, since it is irrelevant for these ivgens.
> +         * This is for compat with dm-crypt which will silently
> +         * ignore hash names with these ivgens rather than report
> +         * an error about the invalid usage
> +         */
> +        luks->ivgen_cipher_alg = luks->cipher_alg;
> +    }
> +    ret = 0;
> +out:
> +    return ret;
> +
> +}
> +
>  /*
>   * Given a key slot, and user password, this will attempt to unlock
>   * the master encryption key from the key slot.
> @@ -720,12 +862,9 @@ qcrypto_block_luks_open(QCryptoBlock *block,
>                          Error **errp)
>  {
>      QCryptoBlockLUKS *luks = NULL;
> -    Error *local_err = NULL;
>      int ret = 0;
>      g_autofree uint8_t *masterkey = NULL;
> -    char *ivgen_name, *ivhash_name;
>      g_autofree char *password = NULL;
> -    g_autofree char *cipher_mode = NULL;
>  
>      if (!(flags & QCRYPTO_BLOCK_OPEN_NO_IO)) {
>          if (!options->u.luks.key_secret) {
> @@ -748,117 +887,16 @@ qcrypto_block_luks_open(QCryptoBlock *block,
>          goto fail;
>      }
>  
> -
> -    if (memcmp(luks->header.magic, qcrypto_block_luks_magic,
> -               QCRYPTO_BLOCK_LUKS_MAGIC_LEN) != 0) {
> -        error_setg(errp, "Volume is not in LUKS format");
> -        ret = -EINVAL;

I can't remember why I set ret to an errno in my original code.
it is entirely pointless, as the caller of this method merely
checks "ret < 0" and doesn't do anything else with the return
value. IOW, we should just purge the errnors from this existing
code entirely.


Regards,
Daniel
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