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Message-Id: <CSIYF14C6N58.7IDA6DAC9NHF@suppilovahvero>
Date: Thu, 11 May 2023 01:34:17 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Eric Snowberg" <eric.snowberg@...cle.com>, <zohar@...ux.ibm.com>,
<dhowells@...hat.com>, <dwmw2@...radead.org>
Cc: <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
<dmitry.kasatkin@...il.com>, <paul@...l-moore.com>,
<jmorris@...ei.org>, <serge@...lyn.com>, <jlee@...e.com>,
<kanth.ghatraju@...cle.com>, <konrad.wilk@...cle.com>,
<keyrings@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<linux-crypto@...r.kernel.org>, <linux-integrity@...r.kernel.org>,
<linux-security-module@...r.kernel.org>
Subject: Re: [PATCH 1/3] KEYS: DigitalSignature link restriction
On Tue May 9, 2023 at 1:07 AM EEST, Eric Snowberg wrote:
> Add a new link restriction. Restrict the addition of keys in a keyring
> based on the key having digitalSignature usage set. Additionally, verify
> the new certificate against the ones in the system keyrings. Add two
> additional functions to use the new restriction within either the builtin
> or secondary keyrings.
>
> Signed-off-by: Eric Snowberg <eric.snowberg@...cle.com>
> ---
> certs/system_keyring.c | 52 +++++++++++++++++++++++++++++++
> crypto/asymmetric_keys/restrict.c | 44 ++++++++++++++++++++++++++
> include/crypto/public_key.h | 11 +++++++
> include/keys/system_keyring.h | 11 +++++++
> 4 files changed, 118 insertions(+)
>
> diff --git a/certs/system_keyring.c b/certs/system_keyring.c
> index a7a49b17ceb1..4249c49bd43b 100644
> --- a/certs/system_keyring.c
> +++ b/certs/system_keyring.c
> @@ -51,6 +51,27 @@ int restrict_link_by_builtin_trusted(struct key *dest_keyring,
> builtin_trusted_keys);
> }
>
> +/**
> + * restrict_link_by_digsig_builtin - Restrict digitalSignature key additions
> + * by the built-in keyring.
BTW, does checkpatch complain if you put that to a single line (I don't
know this)?
If not, I would just put "Restrict by digitalSignature"
> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @restriction_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 the built in system keyring. The new key
> + * must have the digitalSignature usage field set.
> + */
> +int restrict_link_by_digsig_builtin(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *restriction_key)
> +{
> + return restrict_link_by_digsig(dest_keyring, type, payload,
> + builtin_trusted_keys);
> +}
> +
> #ifdef CONFIG_SECONDARY_TRUSTED_KEYRING
> /**
> * restrict_link_by_builtin_and_secondary_trusted - Restrict keyring
> @@ -83,6 +104,37 @@ int restrict_link_by_builtin_and_secondary_trusted(
> secondary_trusted_keys);
> }
>
> +/**
> + * restrict_link_by_digsig_builtin_and_secondary - Restrict digitalSignature
> + * key additions by both built-in and secondary keyrings.
> + * @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 or the secondary system
> + * keyrings. The new key must have the digitalSignature usage field set.
> + */
> +int restrict_link_by_digsig_builtin_and_secondary(
> + struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *restrict_key)
> +{
> + /* If we have a secondary trusted keyring, then that contains a link
> + * through to the builtin keyring and the search will follow that link.
> + */
> + if (type == &key_type_keyring &&
> + dest_keyring == secondary_trusted_keys &&
> + payload == &builtin_trusted_keys->payload)
> + /* Allow the builtin keyring to be added to the secondary */
> + return 0;
> +
> + return restrict_link_by_digsig(dest_keyring, type, payload,
> + secondary_trusted_keys);
> +}
> +
> /*
> * Allocate a struct key_restriction for the "builtin and secondary trust"
> * keyring. Only for use in system_trusted_keyring_init().
> diff --git a/crypto/asymmetric_keys/restrict.c b/crypto/asymmetric_keys/restrict.c
> index 276bdb627498..6b69ea40da23 100644
> --- a/crypto/asymmetric_keys/restrict.c
> +++ b/crypto/asymmetric_keys/restrict.c
> @@ -148,6 +148,50 @@ int restrict_link_by_ca(struct key *dest_keyring,
> return 0;
> }
>
> +/**
> + * restrict_link_by_digsig - Restrict additions to a ring of digsig keys
> + * @dest_keyring: Keyring being linked to.
> + * @type: The type of key being added.
> + * @payload: The payload of the new key.
> + * @trust_keyring: A ring of keys that can be used to vouch for the new cert.
> + *
> + * Check if the new certificate has digitalSignature usage set. If it is,
> + * then mark the new certificate as being ok to link. Afterwards verify
> + * the new certificate against the ones in the trust_keyring.
> + *
> + * Returns 0 if the new certificate was accepted, -ENOKEY if the
> + * certificate is not a digsig. -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_digsig(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *trust_keyring)
> +{
> + const struct public_key *pkey;
> +
> + if (type != &key_type_asymmetric)
> + return -EOPNOTSUPP;
> +
> + pkey = payload->data[asym_crypto];
> +
> + if (!pkey)
> + return -ENOPKG;
> +
> + if (!test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
> + return -ENOKEY;
> +
> + if (test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
> + return -ENOKEY;
> +
> + if (test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
> + return -ENOKEY;
> +
> + return restrict_link_by_signature(dest_keyring, type, payload,
> + trust_keyring);
> +}
> +
> 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 653992a6e941..8eb5eff059f3 100644
> --- a/include/crypto/public_key.h
> +++ b/include/crypto/public_key.h
> @@ -80,6 +80,10 @@ extern int restrict_link_by_ca(struct key *dest_keyring,
> const struct key_type *type,
> const union key_payload *payload,
> struct key *trust_keyring);
> +int restrict_link_by_digsig(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,
> @@ -88,6 +92,13 @@ static inline int restrict_link_by_ca(struct key *dest_keyring,
> {
> return 0;
> }
> +static inline int restrict_link_by_digsig(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 *,
> diff --git a/include/keys/system_keyring.h b/include/keys/system_keyring.h
> index 91e080efb918..38f63f1c2cbe 100644
> --- a/include/keys/system_keyring.h
> +++ b/include/keys/system_keyring.h
> @@ -23,10 +23,15 @@ extern int restrict_link_by_builtin_trusted(struct key *keyring,
> const struct key_type *type,
> const union key_payload *payload,
> struct key *restriction_key);
> +int restrict_link_by_digsig_builtin(struct key *dest_keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *restriction_key);
> extern __init int load_module_cert(struct key *keyring);
>
> #else
> #define restrict_link_by_builtin_trusted restrict_link_reject
> +#define restrict_link_by_digsig_builtin restrict_link_reject
>
> static inline __init int load_module_cert(struct key *keyring)
> {
> @@ -41,8 +46,14 @@ extern int restrict_link_by_builtin_and_secondary_trusted(
> const struct key_type *type,
> const union key_payload *payload,
> struct key *restriction_key);
> +extern int restrict_link_by_digsig_builtin_and_secondary(
> + struct key *keyring,
> + const struct key_type *type,
> + const union key_payload *payload,
> + struct key *restriction_key);
> #else
> #define restrict_link_by_builtin_and_secondary_trusted restrict_link_by_builtin_trusted
> +#define restrict_link_by_digsig_builtin_and_secondary restrict_link_by_digsig_builtin
> #endif
>
> #ifdef CONFIG_INTEGRITY_MACHINE_KEYRING
> --
> 2.27.0
BR, Jarkko
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