[PATCH v8 06/17] KEYS: CA link restriction

[Jarkko Sakkinen]

On Tue, 2021-11-23 at 23:41 -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 at oracle.com>

Also here you should extend the story a bit...

/Jarkko

> ---
> v1: Initial version
> v2: Removed secondary keyring references
> v3: Removed restrict_link_by_system_trusted_or_ca
>     Simplify restrict_link_by_ca - only see if the key is a CA
>     Did not add __init in front of restrict_link_by_ca in case
>       restriction could be resued in the future
> v6: Unmodified from v3
> v7: Check for CA restruction in public key
> v8: Fix issue found by build bot when asym keys not defined in the config
> ---
>  crypto/asymmetric_keys/restrict.c | 43 +++++++++++++++++++++++++++++++
>  include/crypto/public_key.h       | 15 +++++++++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> index 84cefe3b3585..a891c598a2aa 100644
> --- a/crypto/asymmetric_keys/restrict.c
> +++ b/crypto/asymmetric_keys/restrict.c
> @@ -108,6 +108,49 @@ 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_signature *sig;
> +       const struct public_key *pkey;
> +
> +       if (type != &key_type_asymmetric)
> +               return -EOPNOTSUPP;
> +
> +       sig = payload->data[asym_auth];
> +       if (!sig)
> +               return -ENOPKG;
> +
> +       if (!sig->auth_ids[0] && !sig->auth_ids[1])
> +               return -ENOKEY;
> +
> +       pkey = payload->data[asym_crypto];
> +       if (!pkey)
> +               return -ENOPKG;
> +
> +       if (!pkey->key_is_ca)
> +               return -ENOKEY;
> +
> +       return public_key_verify_signature(pkey, sig);
> +}
> +
>  static bool match_either_id(const struct asymmetric_key_ids *pair,
>                             const struct asymmetric_key_id *single)
>  {
> diff --git a/include/crypto/public_key.h b/include/crypto/public_key.h
> index 72dcbc06ef9c..06e34d3340c4 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -72,6 +72,21 @@ 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 *);
>