/* 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)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#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 and 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->auth_ids[0] && !sig->auth_ids[1])
                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],
                                  false);
        if (IS_ERR(key))
                return -ENOKEY;

        if (use_builtin_keys && !test_bit(KEY_FLAG_BUILTIN, &key->flags))
                ret = -ENOKEY;
        else
                ret = verify_signature(key, sig);
        key_put(key);
        return ret;
}

static bool match_either_id(const struct asymmetric_key_ids *pair,
                            const struct asymmetric_key_id *single)
{
        return (asymmetric_key_id_same(pair->id[0], single) ||
                asymmetric_key_id_same(pair->id[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->auth_ids[0] && !sig->auth_ids[1])
                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], false);
                        if (IS_ERR(key))
                                key = NULL;
                } else if (trusted->type == &key_type_asymmetric) {
                        const struct asymmetric_key_ids *signer_ids;

                        signer_ids = asymmetric_key_ids(trusted);

                        /*
                         * 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, and
                         * the second is the fallback. If only one
                         * auth_id is present, it may match against
                         * either signer_id. If two auth_ids are
                         * present, the first auth_id must match one
                         * signer_id and the second auth_id must match
                         * the second signer_id.
                         */
                        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->id[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], 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, and 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 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, and 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);
}