[PATCH v8 11/17] KEYS: Introduce link restriction for machine keys

[Darren Kenny]

On Tuesday, 2021-11-23 at 23:41:18 -05, Eric Snowberg wrote:
> Introduce a new link restriction that includes the trusted builtin,
> secondary and machine keys. The restriction is based on the key to be
> added being vouched for by a key in any of these three keyrings.
>
> Suggested-by: Mimi Zohar <zohar at linux.ibm.com>
> Signed-off-by: Eric Snowberg <eric.snowberg at oracle.com>

Reviewed-by: Darren Kenny <darren.kenny at oracle.com>

> ---
> v3: Initial version
> v4: moved code under CONFIG_INTEGRITY_MOK_KEYRING
> v5: Rename to machine keyring
> v6: Change subject name (suggested by Mimi)
>     Rename restrict_link_by_builtin_secondary_and_ca_trusted
>       to restrict_link_by_builtin_secondary_and_machine (suggested by
>       Mimi)
> v7: Unmodified from v6
> v8: Add missing parameter definitions (suggested by Mimi)
> ---
>  certs/system_keyring.c        | 27 +++++++++++++++++++++++++++
>  include/keys/system_keyring.h |  6 ++++++
>  2 files changed, 33 insertions(+)
>
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index bc7e44fc82c2..8a2fd1dc15db 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -99,6 +99,33 @@ void __init set_machine_trusted_keys(struct key *keyring)
>  {
>  	machine_trusted_keys = keyring;
>  }
> +
> +/**
> + * restrict_link_by_builtin_secondary_and_machine - Restrict keyring addition.
> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @restrict_key: A ring of keys that can be used to vouch for the new cert.
> + *
> + * Restrict the addition of keys into a keyring based on the key-to-be-added
> + * being vouched for by a key in either the built-in, the secondary, or
> + * the machine keyrings.
> + */
> +int restrict_link_by_builtin_secondary_and_machine(
> +	struct key *dest_keyring,
> +	const struct key_type *type,
> +	const union key_payload *payload,
> +	struct key *restrict_key)
> +{
> +	if (machine_trusted_keys && type == &key_type_keyring &&
> +	    dest_keyring == secondary_trusted_keys &&
> +	    payload == &machine_trusted_keys->payload)
> +		/* Allow the machine keyring to be added to the secondary */
> +		return 0;
> +
> +	return restrict_link_by_builtin_and_secondary_trusted(dest_keyring, type,
> +							      payload, restrict_key);
> +}
>  #endif
>  
>  /*
> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> index 98c9b10cdc17..2419a735420f 100644
> --- a/include/keys/system_keyring.h
> +++ b/include/keys/system_keyring.h
> @@ -39,8 +39,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
>  #endif
>  
>  #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING
> +extern int restrict_link_by_builtin_secondary_and_machine(
> +	struct key *dest_keyring,
> +	const struct key_type *type,
> +	const union key_payload *payload,
> +	struct key *restrict_key);
>  extern void __init set_machine_trusted_keys(struct key *keyring);
>  #else
> +#define restrict_link_by_builtin_secondary_and_machine restrict_link_by_builtin_trusted
>  static inline void __init set_machine_trusted_keys(struct key *keyring)
>  {
>  }
> -- 
> 2.18.4