Re: [PATCH v5 5/6] KEYS: CA link restriction

[Jarkko Sakkinen]

On Thu, Mar 02, 2023 at 11:46:51AM -0500, Eric Snowberg wrote:
> Add a new link restriction.  Restrict the addition of keys in a keyring
> based on the key to be added being a CA.
> 
> Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>
> Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
> ---
>  crypto/asymmetric_keys/restrict.c | 38 +++++++++++++++++++++++++++++++
>  include/crypto/public_key.h       | 15 ++++++++++++
>  2 files changed, 53 insertions(+)
> 
> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> index 6b1ac5f5896a..48457c6f33f9 100644
> --- a/crypto/asymmetric_keys/restrict.c
> +++ b/crypto/asymmetric_keys/restrict.c
> @@ -108,6 +108,44 @@ int restrict_link_by_signature(struct key *dest_keyring,
>  	return ret;
>  }
>  
> +/**
> + * restrict_link_by_ca - Restrict additions to a ring of CA keys
> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @trust_keyring: Unused.
> + *
> + * Check if the new certificate is a CA. If it is a CA, then mark the new
> + * certificate as being ok to link.
> + *
> + * Returns 0 if the new certificate was accepted, -ENOKEY if the
> + * certificate is not a CA. -ENOPKG if the signature uses unsupported
> + * crypto, or some other error if there is a matching certificate but
> + * the signature check cannot be performed.
> + */
> +int restrict_link_by_ca(struct key *dest_keyring,
> +			const struct key_type *type,
> +			const union key_payload *payload,
> +			struct key *trust_keyring)
> +{
> +	const struct public_key *pkey;
> +
> +	if (type != &key_type_asymmetric)
> +		return -EOPNOTSUPP;
> +
> +	pkey = payload->data[asym_crypto];
> +	if (!pkey)
> +		return -ENOPKG;
> +	if (!test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
> +		return -ENOKEY;
> +	if (!test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
> +		return -ENOKEY;
> +	if (test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
> +		return -ENOKEY;

nit: would be more readable, if conditions were separated by
empty lines.

> +
> +	return 0;
> +}
> +
>  static bool match_either_id(const struct asymmetric_key_id **pair,
>  			    const struct asymmetric_key_id *single)
>  {
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 03c3fb990d59..653992a6e941 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -75,6 +75,21 @@ extern int restrict_link_by_key_or_keyring_chain(struct key *trust_keyring,
>  						 const union key_payload *payload,
>  						 struct key *trusted);
>  
> +#if IS_REACHABLE(CONFIG_ASYMMETRIC_KEY_TYPE)
> +extern int restrict_link_by_ca(struct key *dest_keyring,
> +			       const struct key_type *type,
> +			       const union key_payload *payload,
> +			       struct key *trust_keyring);
> +#else
> +static inline int restrict_link_by_ca(struct key *dest_keyring,
> +				      const struct key_type *type,
> +				      const union key_payload *payload,
> +				      struct key *trust_keyring)
> +{
> +	return 0;
> +}
> +#endif
> +
>  extern int query_asymmetric_key(const struct kernel_pkey_params *,
>  				struct kernel_pkey_query *);
>  
> -- 
> 2.27.0
> 

BR, Jarkko