crypto/asymmetric_keys/restrict.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /* Instantiate a public key crypto key from an X.509 Certificate
  *
  * Copyright (C) 2012, 2016 Red Hat, Inc. All Rights Reserved.
  * Written by David Howells (dhowells@redhat.com)
  */

 #define pr_fmt(fmt) "ASYM: "fmt
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/err.h>
 #include <crypto/public_key.h>
 #include "asymmetric_keys.h"

 static bool use_builtin_keys;
 static struct asymmetric_key_id *ca_keyid;

 #ifndef MODULE
 static struct {
 	struct asymmetric_key_id id;
 	unsigned char data[10];
 } cakey;

 static int __init ca_keys_setup(char *str)
 {
 	if (!str)		/* default system keyring */
 		return 1;

 	if (strncmp(str, "id:", 3) == 0) {
 		struct asymmetric_key_id *p = &cakey.id;
 		size_t hexlen = (strlen(str) - 3) / 2;
 		int ret;

 		if (hexlen == 0 || hexlen > sizeof(cakey.data)) {
 			pr_err("Missing or invalid ca_keys id\n");
 			return 1;
 		}

 		ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
 		if (ret < 0)
 			pr_err("Unparsable ca_keys id hex string\n");
 		else
 			ca_keyid = p;	/* owner key 'id:xxxxxx' */
 	} else if (strcmp(str, "builtin") == 0) {
 		use_builtin_keys = true;
 	}

 	return 1;
 }
 __setup("ca_keys=", ca_keys_setup);
 #endif

 /**
  * restrict_link_by_signature - Restrict additions to a ring of public 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 the new certificate against the ones in the trust keyring.  If one of
  * those is the signing key and validates the new certificate, then mark the
  * new certificate as being trusted.
  *
  * Returns 0 if the new certificate was accepted, -ENOKEY if we couldn't find a
  * matching parent certificate in the trusted list, -EKEYREJECTED if the
  * signature check fails or the key is blacklisted, -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_signature(struct key *dest_keyring,
 			       const struct key_type *type,
 			       const union key_payload *payload,
 			       struct key *trust_keyring)
 {
 	const struct public_key_signature *sig;
 	struct key *key;
 	int ret;

 	pr_devel("==>%s()\n", __func__);

 	if (!trust_keyring)
 		return -ENOKEY;

 	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] && !sig->auth_ids[2])
 		return -ENOKEY;

 	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
 		return -EPERM;

 	/* See if we have a key that signed this one. */
 	key = find_asymmetric_key(trust_keyring,
 				  sig->auth_ids[0], sig->auth_ids[1],
 				  sig->auth_ids[2], false);
 	if (IS_ERR(key))
 		return -ENOKEY;

 	if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
 		ret = -ENOKEY;
 	else if (IS_BUILTIN(CONFIG_SECONDARY_TRUSTED_KEYRING_SIGNED_BY_BUILTIN) &&
 		 !strcmp(dest_keyring->description, ".secondary_trusted_keys") &&
 		 !test_bit(KEY_FLAG_BUILTIN, &key->flags))
 		ret = -ENOKEY;
 	else
 		ret = verify_signature(key, sig);
 	key_put(key);
 	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 *pkey;

 	if (type != &key_type_asymmetric)
 		return -EOPNOTSUPP;

 	pkey = payload->data[asym_crypto];
 	if (!pkey)
 		return -ENOPKG;
 	if (!test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
 		return -ENOKEY;
 	if (!test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
 		return -ENOKEY;
 	if (!IS_ENABLED(CONFIG_INTEGRITY_CA_MACHINE_KEYRING_MAX))
 		return 0;
 	if (test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
 		return -ENOKEY;

 	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)
 {
 	return (asymmetric_key_id_same(pair[0], single) ||
 		asymmetric_key_id_same(pair[1], single));
 }

 static int key_or_keyring_common(struct key *dest_keyring,
 				 const struct key_type *type,
 				 const union key_payload *payload,
 				 struct key *trusted, bool check_dest)
 {
 	const struct public_key_signature *sig;
 	struct key *key = NULL;
 	int ret;

 	pr_devel("==>%s()\n", __func__);

 	if (!dest_keyring)
 		return -ENOKEY;
 	else if (dest_keyring->type != &key_type_keyring)
 		return -EOPNOTSUPP;

 	if (!trusted && !check_dest)
 		return -ENOKEY;

 	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] && !sig->auth_ids[2])
 		return -ENOKEY;

 	if (trusted) {
 		if (trusted->type == &key_type_keyring) {
 			/* See if we have a key that signed this one. */
 			key = find_asymmetric_key(trusted, sig->auth_ids[0],
 						  sig->auth_ids[1],
 						  sig->auth_ids[2], false);
 			if (IS_ERR(key))
 				key = NULL;
 		} else if (trusted->type == &key_type_asymmetric) {
 			const struct asymmetric_key_id **signer_ids;

 			signer_ids = (const struct asymmetric_key_id **)
 				asymmetric_key_ids(trusted)->id;

 			/*
 			 * The auth_ids come from the candidate key (the
 			 * one that is being considered for addition to
 			 * dest_keyring) and identify the key that was
 			 * used to sign.
 			 *
 			 * The signer_ids are identifiers for the
 			 * signing key specified for dest_keyring.
 			 *
 			 * The first auth_id is the preferred id, 2nd and
 			 * 3rd are the fallbacks. If exactly one of
 			 * auth_ids[0] and auth_ids[1] is present, it may
 			 * match either signer_ids[0] or signed_ids[1].
 			 * If both are present the first one may match
 			 * either signed_id but the second one must match
 			 * the second signer_id. If neither of them is
 			 * available, auth_ids[2] is matched against
 			 * signer_ids[2] as a fallback.
 			 */
 			if (!sig->auth_ids[0] && !sig->auth_ids[1]) {
 				if (asymmetric_key_id_same(signer_ids[2],
 							   sig->auth_ids[2]))
 					key = __key_get(trusted);

 			} else if (!sig->auth_ids[0] || !sig->auth_ids[1]) {
 				const struct asymmetric_key_id *auth_id;

 				auth_id = sig->auth_ids[0] ?: sig->auth_ids[1];
 				if (match_either_id(signer_ids, auth_id))
 					key = __key_get(trusted);

 			} else if (asymmetric_key_id_same(signer_ids[1],
 							  sig->auth_ids[1]) &&
 				   match_either_id(signer_ids,
 						   sig->auth_ids[0])) {
 				key = __key_get(trusted);
 			}
 		} else {
 			return -EOPNOTSUPP;
 		}
 	}

 	if (check_dest && !key) {
 		/* See if the destination has a key that signed this one. */
 		key = find_asymmetric_key(dest_keyring, sig->auth_ids[0],
 					  sig->auth_ids[1], sig->auth_ids[2],
 					  false);
 		if (IS_ERR(key))
 			key = NULL;
 	}

 	if (!key)
 		return -ENOKEY;

 	ret = key_validate(key);
 	if (ret == 0)
 		ret = verify_signature(key, sig);

 	key_put(key);
 	return ret;
 }

 /**
  * restrict_link_by_key_or_keyring - Restrict additions to a ring of public
  * keys using the restrict_key information stored in the ring.
  * @dest_keyring: Keyring being linked to.
  * @type: The type of key being added.
  * @payload: The payload of the new key.
  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
  *
  * Check the new certificate only against the key or keys passed in the data
  * parameter. If one of those is the signing key and validates the new
  * certificate, then mark the new certificate as being ok to link.
  *
  * Returns 0 if the new certificate was accepted, -ENOKEY if we
  * couldn't find a matching parent certificate in the trusted list,
  * -EKEYREJECTED if the signature check fails, -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_key_or_keyring(struct key *dest_keyring,
 				    const struct key_type *type,
 				    const union key_payload *payload,
 				    struct key *trusted)
 {
 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
 				     false);
 }

 /**
  * restrict_link_by_key_or_keyring_chain - Restrict additions to a ring of
  * public keys using the restrict_key information stored in the ring.
  * @dest_keyring: Keyring being linked to.
  * @type: The type of key being added.
  * @payload: The payload of the new key.
  * @trusted: A key or ring of keys that can be used to vouch for the new cert.
  *
  * Check the new certificate against the key or keys passed in the data
  * parameter and against the keys already linked to the destination keyring. If
  * one of those is the signing key and validates the new certificate, then mark
  * the new certificate as being ok to link.
  *
  * Returns 0 if the new certificate was accepted, -ENOKEY if we
  * couldn't find a matching parent certificate in the trusted list,
  * -EKEYREJECTED if the signature check fails, -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_key_or_keyring_chain(struct key *dest_keyring,
 					  const struct key_type *type,
 					  const union key_payload *payload,
 					  struct key *trusted)
 {
 	return key_or_keyring_common(dest_keyring, type, payload, trusted,
 				     true);
 }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/* Instantiate a public key crypto key from an X.509 Certificate
	*
	* Copyright (C) 2012, 2016 Red Hat, Inc. All Rights Reserved.
	* Written by David Howells (dhowells@redhat.com)
	*/

	#define pr_fmt(fmt) "ASYM: "fmt
	#include <linux/module.h>
	#include <linux/kernel.h>
	#include <linux/err.h>
	#include <crypto/public_key.h>
	#include "asymmetric_keys.h"

	static bool use_builtin_keys;
	static struct asymmetric_key_id *ca_keyid;

	#ifndef MODULE
	static struct {
	struct asymmetric_key_id id;
	unsigned char data[10];
	} cakey;

	static int __init ca_keys_setup(char *str)
	{
	if (!str) /* default system keyring */
	return 1;

	if (strncmp(str, "id:", 3) == 0) {
	struct asymmetric_key_id *p = &cakey.id;
	size_t hexlen = (strlen(str) - 3) / 2;
	int ret;

	if (hexlen == 0 \|\| hexlen > sizeof(cakey.data)) {
	pr_err("Missing or invalid ca_keys id\n");
	return 1;
	}

	ret = __asymmetric_key_hex_to_key_id(str + 3, p, hexlen);
	if (ret < 0)
	pr_err("Unparsable ca_keys id hex string\n");
	else
	ca_keyid = p; /* owner key 'id:xxxxxx' */
	} else if (strcmp(str, "builtin") == 0) {
	use_builtin_keys = true;
	}

	return 1;
	}
	__setup("ca_keys=", ca_keys_setup);
	#endif

	/**
	* restrict_link_by_signature - Restrict additions to a ring of public 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 the new certificate against the ones in the trust keyring. If one of
	* those is the signing key and validates the new certificate, then mark the
	* new certificate as being trusted.
	*
	* Returns 0 if the new certificate was accepted, -ENOKEY if we couldn't find a
	* matching parent certificate in the trusted list, -EKEYREJECTED if the
	* signature check fails or the key is blacklisted, -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_signature(struct key *dest_keyring,
	const struct key_type *type,
	const union key_payload *payload,
	struct key *trust_keyring)
	{
	const struct public_key_signature *sig;
	struct key *key;
	int ret;

	pr_devel("==>%s()\n", __func__);

	if (!trust_keyring)
	return -ENOKEY;

	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] && !sig->auth_ids[2])
	return -ENOKEY;

	if (ca_keyid && !asymmetric_key_id_partial(sig->auth_ids[1], ca_keyid))
	return -EPERM;

	/* See if we have a key that signed this one. */
	key = find_asymmetric_key(trust_keyring,
	sig->auth_ids[0], sig->auth_ids[1],
	sig->auth_ids[2], false);
	if (IS_ERR(key))
	return -ENOKEY;

	if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
	ret = -ENOKEY;
	else if (IS_BUILTIN(CONFIG_SECONDARY_TRUSTED_KEYRING_SIGNED_BY_BUILTIN) &&
	!strcmp(dest_keyring->description, ".secondary_trusted_keys") &&
	!test_bit(KEY_FLAG_BUILTIN, &key->flags))
	ret = -ENOKEY;
	else
	ret = verify_signature(key, sig);
	key_put(key);
	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 *pkey;

	if (type != &key_type_asymmetric)
	return -EOPNOTSUPP;

	pkey = payload->data[asym_crypto];
	if (!pkey)
	return -ENOPKG;
	if (!test_bit(KEY_EFLAG_CA, &pkey->key_eflags))
	return -ENOKEY;
	if (!test_bit(KEY_EFLAG_KEYCERTSIGN, &pkey->key_eflags))
	return -ENOKEY;
	if (!IS_ENABLED(CONFIG_INTEGRITY_CA_MACHINE_KEYRING_MAX))
	return 0;
	if (test_bit(KEY_EFLAG_DIGITALSIG, &pkey->key_eflags))
	return -ENOKEY;

	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)
	{
	return (asymmetric_key_id_same(pair[0], single) \|\|
	asymmetric_key_id_same(pair[1], single));
	}

	static int key_or_keyring_common(struct key *dest_keyring,
	const struct key_type *type,
	const union key_payload *payload,
	struct key *trusted, bool check_dest)
	{
	const struct public_key_signature *sig;
	struct key *key = NULL;
	int ret;

	pr_devel("==>%s()\n", __func__);

	if (!dest_keyring)
	return -ENOKEY;
	else if (dest_keyring->type != &key_type_keyring)
	return -EOPNOTSUPP;

	if (!trusted && !check_dest)
	return -ENOKEY;

	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] && !sig->auth_ids[2])
	return -ENOKEY;

	if (trusted) {
	if (trusted->type == &key_type_keyring) {
	/* See if we have a key that signed this one. */
	key = find_asymmetric_key(trusted, sig->auth_ids[0],
	sig->auth_ids[1],
	sig->auth_ids[2], false);
	if (IS_ERR(key))
	key = NULL;
	} else if (trusted->type == &key_type_asymmetric) {
	const struct asymmetric_key_id **signer_ids;

	signer_ids = (const struct asymmetric_key_id **)
	asymmetric_key_ids(trusted)->id;

	/*
	* The auth_ids come from the candidate key (the
	* one that is being considered for addition to
	* dest_keyring) and identify the key that was
	* used to sign.
	*
	* The signer_ids are identifiers for the
	* signing key specified for dest_keyring.
	*
	* The first auth_id is the preferred id, 2nd and
	* 3rd are the fallbacks. If exactly one of
	* auth_ids[0] and auth_ids[1] is present, it may
	* match either signer_ids[0] or signed_ids[1].
	* If both are present the first one may match
	* either signed_id but the second one must match
	* the second signer_id. If neither of them is
	* available, auth_ids[2] is matched against
	* signer_ids[2] as a fallback.
	*/
	if (!sig->auth_ids[0] && !sig->auth_ids[1]) {
	if (asymmetric_key_id_same(signer_ids[2],
	sig->auth_ids[2]))
	key = __key_get(trusted);

	} else if (!sig->auth_ids[0] \|\| !sig->auth_ids[1]) {
	const struct asymmetric_key_id *auth_id;

	auth_id = sig->auth_ids[0] ?: sig->auth_ids[1];
	if (match_either_id(signer_ids, auth_id))
	key = __key_get(trusted);

	} else if (asymmetric_key_id_same(signer_ids[1],
	sig->auth_ids[1]) &&
	match_either_id(signer_ids,
	sig->auth_ids[0])) {
	key = __key_get(trusted);
	}
	} else {
	return -EOPNOTSUPP;
	}
	}

	if (check_dest && !key) {
	/* See if the destination has a key that signed this one. */
	key = find_asymmetric_key(dest_keyring, sig->auth_ids[0],
	sig->auth_ids[1], sig->auth_ids[2],
	false);
	if (IS_ERR(key))
	key = NULL;
	}

	if (!key)
	return -ENOKEY;

	ret = key_validate(key);
	if (ret == 0)
	ret = verify_signature(key, sig);

	key_put(key);
	return ret;
	}

	/**
	* restrict_link_by_key_or_keyring - Restrict additions to a ring of public
	* keys using the restrict_key information stored in the ring.
	* @dest_keyring: Keyring being linked to.
	* @type: The type of key being added.
	* @payload: The payload of the new key.
	* @trusted: A key or ring of keys that can be used to vouch for the new cert.
	*
	* Check the new certificate only against the key or keys passed in the data
	* parameter. If one of those is the signing key and validates the new
	* certificate, then mark the new certificate as being ok to link.
	*
	* Returns 0 if the new certificate was accepted, -ENOKEY if we
	* couldn't find a matching parent certificate in the trusted list,
	* -EKEYREJECTED if the signature check fails, -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_key_or_keyring(struct key *dest_keyring,
	const struct key_type *type,
	const union key_payload *payload,
	struct key *trusted)
	{
	return key_or_keyring_common(dest_keyring, type, payload, trusted,
	false);
	}

	/**
	* restrict_link_by_key_or_keyring_chain - Restrict additions to a ring of
	* public keys using the restrict_key information stored in the ring.
	* @dest_keyring: Keyring being linked to.
	* @type: The type of key being added.
	* @payload: The payload of the new key.
	* @trusted: A key or ring of keys that can be used to vouch for the new cert.
	*
	* Check the new certificate against the key or keys passed in the data
	* parameter and against the keys already linked to the destination keyring. If
	* one of those is the signing key and validates the new certificate, then mark
	* the new certificate as being ok to link.
	*
	* Returns 0 if the new certificate was accepted, -ENOKEY if we
	* couldn't find a matching parent certificate in the trusted list,
	* -EKEYREJECTED if the signature check fails, -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_key_or_keyring_chain(struct key *dest_keyring,
	const struct key_type *type,
	const union key_payload *payload,
	struct key *trusted)
	{
	return key_or_keyring_common(dest_keyring, type, payload, trusted,
	true);
	}