linux/crypto/asymmetric_keys/restrict.c
Mimi Zohar b46503068c certs: Only allow certs signed by keys on the builtin keyring
Originally the secondary trusted keyring provided a keyring to which extra
keys may be added, provided those keys were not blacklisted and were
vouched for by a key built into the kernel or already in the secondary
trusted keyring.

On systems with the machine keyring configured, additional keys may also
be vouched for by a key on the machine keyring.

Prevent loading additional certificates directly onto the secondary
keyring, vouched for by keys on the machine keyring, yet allow these
certificates to be loaded onto other trusted keyrings.

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
2023-10-31 08:22:36 -04:00

364 lines
11 KiB
C

// 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);
}