Re: [RFC PATCH 1/1] crypto: af_alg - Support symmetric encryption via keyring keys

[Eric Biggers]

Hi Frederick,

On Tue, Oct 04, 2022 at 04:29:27PM -0500, Frederick Lawler wrote:
> We want to leverage keyring to store sensitive keys, and then use those
> keys for symmetric encryption via the crypto API. Among the key types we
> wish to support are: user, logon, encrypted, and trusted.
> 
> User key types are already able to have their data copied to user space,
> but logon does not support this. Further, trusted and encrypted keys will
> return their encrypted data back to user space on read, which make them not
> ideal for symmetric encryption.
> 
> To support symmetric encryption for these key types, add a new
> ALG_SET_KEY_BY_KEY_SERIAL setsockopt() option to the crypto API. This
> allows users to pass a key_serial_t to the crypto API to perform
> symmetric encryption. The behavior is the same as ALG_SET_KEY, but
> the crypto key data is copied in kernel space from a keyring key,
> which allows for the support of logon, encrypted, and trusted key types.
> 
> Keyring keys must have the KEY_(POS|USR|GRP|OTH)_SEARCH permission set
> to leverage this feature. This follows the asymmetric_key type where key
> lookup calls eventually lead to keyring_search_rcu() without the
> KEYRING_SEARCH_NO_CHECK_PERM flag set.
> 
> Signed-off-by: Frederick Lawler <fred@xxxxxxxxxxxxxx>

There was a similar patch several years ago by Ondrej Mosnacek:
https://lore.kernel.org/linux-crypto/20190521100034.9651-1-omosnace@xxxxxxxxxx/T/#u

Have you addressed all the feedback that was raised on that one?

Two random nits below:

> +	*dest_len = key->datalen;
> +	*dest = kmalloc(*dest_len, GFP_KERNEL);
> +	if (!*dest)
> +		return -ENOMEM;
> +
> +	memcpy(*dest, ukp->data, *dest_len);

This should use kmemdup().

> +	} else if (IS_ENABLED(CONFIG_ENCRYPTED_KEYS) &&
> +			   !strcmp(key->type->name, "encrypted")) {
> +		read_key = &read_key_type_encrypted;
> +	} else if (IS_ENABLED(CONFIG_TRUSTED_KEYS) &&
> +			   !strcmp(key->type->name, "trusted")) {
> +		read_key = &read_key_type_trusted;

These need to use IS_REACHABLE(), not IS_ENABLED().

- Eric