linux-kernel - Re: [PATCH 3/4] KEYS: CA link restriction

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Date:   Fri, 4 Mar 2022 10:28:11 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Eric Snowberg <eric.snowberg@...cle.com>, zohar@...ux.ibm.com,
        jarkko@...nel.org, dhowells@...hat.com, dwmw2@...radead.org
Cc:     herbert@...dor.apana.org.au, davem@...emloft.net,
        jmorris@...ei.org, serge@...lyn.com, nayna@...ux.ibm.com,
        mic@...ux.microsoft.com, konrad.wilk@...cle.com,
        keyrings@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 3/4] KEYS: CA link restriction


On 3/1/22 12:36, 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@...cle.com>
> ---
>   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 6b1ac5f5896a..49bb2ea7f609 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.

CA = root CA here, right?


> + *
> + * 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)
This function needs to correspond to the key_restrict_link_func_t and 
therefore has 4 parameter. Call the unused 'trust_keyring' 'unused' instead?
> +{
> +	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);
> +}
> +

Comparing this to 'restrict_link_by_signature'... looks good.


>   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 0521241764b7..5eadb182a400 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 *);
>