Re: [RFC PATCH v3 02/13] certs: Introduce ability to link to a system key

[Mimi Zohar]

On Thu, 2024-10-17 at 09:55 -0600, Eric Snowberg wrote:
> Introduce system_key_link(), a new function to allow a keyring to link
> to a key contained within one of the system keyrings (builtin, secondary,
> or platform). Depending on how the kernel is built, if the machine
> keyring is available, it will be checked as well, since it is linked to
> the secondary keyring. If the asymmetric key id matches a key within one
> of these system keyrings, the matching key is linked into the passed in
> keyring.
> 
> Signed-off-by: Eric Snowberg <eric.snowberg@xxxxxxxxxx>

Reviewed-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>

> ---
>  certs/system_keyring.c        | 30 ++++++++++++++++++++++++++++++
>  include/keys/system_keyring.h |  7 ++++++-
>  2 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index e344cee10d28..4abee7514442 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -20,6 +20,9 @@
>  static struct key *builtin_trusted_keys;
>  #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
>  static struct key *secondary_trusted_keys;
> +#define system_trusted_keys secondary_trusted_keys
> +#else
> +#define system_trusted_keys builtin_trusted_keys
>  #endif
>  #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING
>  static struct key *machine_trusted_keys;
> @@ -420,3 +423,30 @@ void __init set_platform_trusted_keys(struct key *keyring)
>  	platform_trusted_keys = keyring;
>  }
>  #endif
> +
> +/**
> + * system_key_link - Link to a system key
> + * @keyring: The keyring to link into
> + * @id: The asymmetric key id to look for in the system keyring
> + *
> + * Search the system keyrings to see if one of them contains a matching "id".
> + * If there is a match, link the key into "keyring".  System keyrings always
> + * includes the builtin. If any of the following keyrings are enabled:
> + * secondary, machine, and platform they are searched as well.
> + */
> +int system_key_link(struct key *keyring, struct asymmetric_key_id *id)
> +{
> +	struct key *key;
> +
> +	key = find_asymmetric_key(system_trusted_keys, id, NULL, NULL, false);
> +	if (!IS_ERR(key))
> +		return key_link(keyring, key);
> +
> +	if (platform_trusted_keys) {
> +		key = find_asymmetric_key(platform_trusted_keys, id, NULL, NULL, false);
> +		if (!IS_ERR(key))
> +			return key_link(keyring, key);
> +	}
> +
> +	return -ENOKEY;
> +}
> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> index 8365adf842ef..b47ac8e2001a 100644
> --- a/include/keys/system_keyring.h
> +++ b/include/keys/system_keyring.h
> @@ -9,6 +9,7 @@
>  #define _KEYS_SYSTEM_KEYRING_H
>  
>  #include <linux/key.h>
> +struct asymmetric_key_id;
>  
>  enum blacklist_hash_type {
>  	/* TBSCertificate hash */
> @@ -28,7 +29,7 @@ int restrict_link_by_digsig_builtin(struct key *dest_keyring,
>  				    const union key_payload *payload,
>  				    struct key *restriction_key);
>  extern __init int load_module_cert(struct key *keyring);
> -
> +extern int system_key_link(struct key *keyring, struct asymmetric_key_id *id);
>  #else
>  #define restrict_link_by_builtin_trusted restrict_link_reject
>  #define restrict_link_by_digsig_builtin restrict_link_reject
> @@ -38,6 +39,10 @@ static inline __init int load_module_cert(struct key *keyring)
>  	return 0;
>  }
>  
> +static inline int system_key_link(struct key *keyring, struct asymmetric_key_id *id)
> +{
> +	return 0;
> +}
>  #endif
>  
>  #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING