linux-kernel - Re: [RFC PATCH v2 1/8] certs: Introduce ability to link to a system key

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Message-Id: <D1RFM5ZWU1O4.1QU546DO1UNKD@kernel.org>
Date: Tue, 04 Jun 2024 21:08:00 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Eric Snowberg" <eric.snowberg@...cle.com>,
 <linux-security-module@...r.kernel.org>
Cc: <dhowells@...hat.com>, <dwmw2@...radead.org>,
 <herbert@...dor.apana.org.au>, <davem@...emloft.net>, <ardb@...nel.org>,
 <paul@...l-moore.com>, <jmorris@...ei.org>, <serge@...lyn.com>,
 <zohar@...ux.ibm.com>, <roberto.sassu@...wei.com>,
 <dmitry.kasatkin@...il.com>, <mic@...ikod.net>, <casey@...aufler-ca.com>,
 <stefanb@...ux.ibm.com>, <ebiggers@...nel.org>, <rdunlap@...radead.org>,
 <linux-kernel@...r.kernel.org>, <keyrings@...r.kernel.org>,
 <linux-crypto@...r.kernel.org>, <linux-efi@...r.kernel.org>,
 <linux-integrity@...r.kernel.org>
Subject: Re: [RFC PATCH v2 1/8] certs: Introduce ability to link to a system
 key

On Fri May 31, 2024 at 3:39 AM EEST, Eric Snowberg wrote:
> Introduce a new function to allow a keyring to link to a key contained
> within one of the system keyrings (builtin, secondary, or platform).

"Introduce system_key_link(), a new function..."

I hate when the exact thing added is not immediately transparent from
the commit message ;-) Helps a lot when bisecting for instance.

> 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@...cle.com>
> ---
>  certs/system_keyring.c        | 31 +++++++++++++++++++++++++++++++
>  include/keys/system_keyring.h |  7 ++++++-
>  2 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index 9de610bf1f4b..94e47b6b3333 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -426,3 +426,34 @@ void __init set_platform_trusted_keys(struct key *keyring)
>  	platform_trusted_keys = keyring;
>  }
>  #endif
> +
> +/**
> + * system_key_link - Link to a system key

"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
> + */

Really could use some overview keyrings traversed just as a reminder.

> +int system_key_link(struct key *keyring, struct asymmetric_key_id *id)
> +{
> +	struct key *system_keyring;
> +	struct key *key;
> +
> +#ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
> +	system_keyring = secondary_trusted_keys;
> +#else
> +	system_keyring = builtin_trusted_keys;
> +#endif

Why not simply make secondary_trusted_keys in the first place be alias
to builtin_trusted_keys when it is not enabled?

> +
> +	key = find_asymmetric_key(system_keyring, id, NULL, NULL, false);
> +	if (!IS_ERR(key))
> +		goto found;
> +
> +	key = find_asymmetric_key(platform_trusted_keys, id, NULL, NULL, false);
> +	if (!IS_ERR(key))
> +		goto found;
> +
> +	return -ENOKEY;
> +
> +found:

"link:"?

Then you could see already from goto statement what will happen next
(your call anyway).

> +	key_link(keyring, key);
> +	return 0;
> +}
> 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

BR, Jarkko