/* Instantiate a public key crypto key from an X.509 Certificate
 *
 * Copyright (C) 2012 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) "X.509: "fmt
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <keys/asymmetric-subtype.h>
#include <keys/asymmetric-parser.h>
#include <keys/system_keyring.h>
#include <crypto/hash.h>
#include "asymmetric_keys.h"
#include "x509_parser.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

/**
 * x509_request_asymmetric_key - Request a key by X.509 certificate params.
 * @keyring: The keys to search.
 * @id: The issuer & serialNumber to look for or NULL.
 * @skid: The subjectKeyIdentifier to look for or NULL.
 * @partial: Use partial match if true, exact if false.
 *
 * Find a key in the given keyring by identifier.  The preferred identifier is
 * the issuer + serialNumber and the fallback identifier is the
 * subjectKeyIdentifier.  If both are given, the lookup is by the former, but
 * the latter must also match.
 */
struct key *x509_request_asymmetric_key(struct key *keyring,
                                        const struct asymmetric_key_id *id,
                                        const struct asymmetric_key_id *skid,
                                        bool partial)
{
        struct key *key;
        key_ref_t ref;
        const char *lookup;
        char *req, *p;
        int len;

        if (id) {
                lookup = id->data;
                len = id->len;
        } else {
                lookup = skid->data;
                len = skid->len;
        }
        
        /* Construct an identifier "id:<keyid>". */
        p = req = kmalloc(2 + 1 + len * 2 + 1, GFP_KERNEL);
        if (!req)
                return ERR_PTR(-ENOMEM);

        if (partial) {
                *p++ = 'i';
                *p++ = 'd';
        } else {
                *p++ = 'e';
                *p++ = 'x';
        }
        *p++ = ':';
        p = bin2hex(p, lookup, len);
        *p = 0;

        pr_debug("Look up: \"%s\"\n", req);

        ref = keyring_search(make_key_ref(keyring, 1),
                             &key_type_asymmetric, req);
        if (IS_ERR(ref))
                pr_debug("Request for key '%s' err %ld\n", req, PTR_ERR(ref));
        kfree(req);

        if (IS_ERR(ref)) {
                switch (PTR_ERR(ref)) {
                        /* Hide some search errors */
                case -EACCES:
                case -ENOTDIR:
                case -EAGAIN:
                        return ERR_PTR(-ENOKEY);
                default:
                        return ERR_CAST(ref);
                }
        }

        key = key_ref_to_ptr(ref);
        if (id && skid) {
                const struct asymmetric_key_ids *kids = asymmetric_key_ids(key);
                if (!kids->id[1]) {
                        pr_debug("issuer+serial match, but expected SKID missing\n");
                        goto reject;
                }
                if (!asymmetric_key_id_same(skid, kids->id[1])) {
                        pr_debug("issuer+serial match, but SKID does not\n");
                        goto reject;
                }
        }
        
        pr_devel("<==%s() = 0 [%x]\n", __func__, key_serial(key));
        return key;

reject:
        key_put(key);
        return ERR_PTR(-EKEYREJECTED);
}
EXPORT_SYMBOL_GPL(x509_request_asymmetric_key);

/*
 * Set up the signature parameters in an X.509 certificate.  This involves
 * digesting the signed data and extracting the signature.
 */
int x509_get_sig_params(struct x509_certificate *cert)
{
        struct crypto_shash *tfm;
        struct shash_desc *desc;
        size_t digest_size, desc_size;
        void *digest;
        int ret;

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

        if (cert->unsupported_crypto)
                return -ENOPKG;
        if (cert->sig.s)
                return 0;

        cert->sig.s = kmemdup(cert->raw_sig, cert->raw_sig_size,
                              GFP_KERNEL);
        if (!cert->sig.s)
                return -ENOMEM;

        cert->sig.s_size = cert->raw_sig_size;

        /* Allocate the hashing algorithm we're going to need and find out how
         * big the hash operational data will be.
         */
        tfm = crypto_alloc_shash(cert->sig.hash_algo, 0, 0);
        if (IS_ERR(tfm)) {
                if (PTR_ERR(tfm) == -ENOENT) {
                        cert->unsupported_crypto = true;
                        return -ENOPKG;
                }
                return PTR_ERR(tfm);
        }

        desc_size = crypto_shash_descsize(tfm) + sizeof(*desc);
        digest_size = crypto_shash_digestsize(tfm);

        /* We allocate the hash operational data storage on the end of the
         * digest storage space.
         */
        ret = -ENOMEM;
        digest = kzalloc(ALIGN(digest_size, __alignof__(*desc)) + desc_size,
                         GFP_KERNEL);
        if (!digest)
                goto error;

        cert->sig.digest = digest;
        cert->sig.digest_size = digest_size;

        desc = PTR_ALIGN(digest + digest_size, __alignof__(*desc));
        desc->tfm = tfm;
        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

        ret = crypto_shash_init(desc);
        if (ret < 0)
                goto error;
        might_sleep();
        ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, digest);
error:
        crypto_free_shash(tfm);
        pr_devel("<==%s() = %d\n", __func__, ret);
        return ret;
}
EXPORT_SYMBOL_GPL(x509_get_sig_params);

/*
 * Check the signature on a certificate using the provided public key
 */
int x509_check_signature(const struct public_key *pub,
                         struct x509_certificate *cert)
{
        int ret;

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

        ret = x509_get_sig_params(cert);
        if (ret < 0)
                return ret;

        ret = public_key_verify_signature(pub, &cert->sig);
        if (ret == -ENOPKG)
                cert->unsupported_crypto = true;
        pr_debug("Cert Verification: %d\n", ret);
        return ret;
}
EXPORT_SYMBOL_GPL(x509_check_signature);

/*
 * 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.
 *
 * Return 0 if the new certificate was successfully validated, 1 if we couldn't
 * find a matching parent certificate in the trusted list and an error if there
 * is a matching certificate but the signature check fails.
 */
static int x509_validate_trust(struct x509_certificate *cert,
                               struct key *trust_keyring)
{
        struct key *key;
        int ret = 1;

        if (!trust_keyring)
                return -EOPNOTSUPP;

        if (ca_keyid && !asymmetric_key_id_partial(cert->akid_skid, ca_keyid))
                return -EPERM;

        key = x509_request_asymmetric_key(trust_keyring,
                                          cert->akid_id, cert->akid_skid,
                                          false);
        if (!IS_ERR(key))  {
                if (!use_builtin_keys
                    || test_bit(KEY_FLAG_BUILTIN, &key->flags))
                        ret = x509_check_signature(key->payload.data[asym_crypto],
                                                   cert);
                key_put(key);
        }
        return ret;
}

/*
 * Attempt to parse a data blob for a key as an X509 certificate.
 */
static int x509_key_preparse(struct key_preparsed_payload *prep)
{
        struct asymmetric_key_ids *kids;
        struct x509_certificate *cert;
        const char *q;
        size_t srlen, sulen;
        char *desc = NULL, *p;
        int ret;

        cert = x509_cert_parse(prep->data, prep->datalen);
        if (IS_ERR(cert))
                return PTR_ERR(cert);

        pr_devel("Cert Issuer: %s\n", cert->issuer);
        pr_devel("Cert Subject: %s\n", cert->subject);

        if (!cert->pub->pkey_algo ||
            !cert->sig.pkey_algo ||
            !cert->sig.hash_algo) {
                ret = -ENOPKG;
                goto error_free_cert;
        }

        pr_devel("Cert Key Algo: %s\n", cert->pub->pkey_algo);
        pr_devel("Cert Valid period: %lld-%lld\n", cert->valid_from, cert->valid_to);
        pr_devel("Cert Signature: %s + %s\n",
                 cert->sig.pkey_algo,
                 cert->sig.hash_algo);

        cert->pub->id_type = "X509";

        /* Check the signature on the key if it appears to be self-signed */
        if ((!cert->akid_skid && !cert->akid_id) ||
            asymmetric_key_id_same(cert->skid, cert->akid_skid) ||
            asymmetric_key_id_same(cert->id, cert->akid_id)) {
                ret = x509_check_signature(cert->pub, cert); /* self-signed */
                if (ret < 0)
                        goto error_free_cert;
        } else if (!prep->trusted) {
                ret = x509_validate_trust(cert, get_system_trusted_keyring());
                if (ret)
                        ret = x509_validate_trust(cert, get_ima_mok_keyring());
                if (!ret)
                        prep->trusted = 1;
        }

        /* Propose a description */
        sulen = strlen(cert->subject);
        if (cert->raw_skid) {
                srlen = cert->raw_skid_size;
                q = cert->raw_skid;
        } else {
                srlen = cert->raw_serial_size;
                q = cert->raw_serial;
        }

        ret = -ENOMEM;
        desc = kmalloc(sulen + 2 + srlen * 2 + 1, GFP_KERNEL);
        if (!desc)
                goto error_free_cert;
        p = memcpy(desc, cert->subject, sulen);
        p += sulen;
        *p++ = ':';
        *p++ = ' ';
        p = bin2hex(p, q, srlen);
        *p = 0;

        kids = kmalloc(sizeof(struct asymmetric_key_ids), GFP_KERNEL);
        if (!kids)
                goto error_free_desc;
        kids->id[0] = cert->id;
        kids->id[1] = cert->skid;

        /* We're pinning the module by being linked against it */
        __module_get(public_key_subtype.owner);
        prep->payload.data[asym_subtype] = &public_key_subtype;
        prep->payload.data[asym_key_ids] = kids;
        prep->payload.data[asym_crypto] = cert->pub;
        prep->description = desc;
        prep->quotalen = 100;

        /* We've finished with the certificate */
        cert->pub = NULL;
        cert->id = NULL;
        cert->skid = NULL;
        desc = NULL;
        ret = 0;

error_free_desc:
        kfree(desc);
error_free_cert:
        x509_free_certificate(cert);
        return ret;
}

static struct asymmetric_key_parser x509_key_parser = {
        .owner  = THIS_MODULE,
        .name   = "x509",
        .parse  = x509_key_preparse,
};

/*
 * Module stuff
 */
static int __init x509_key_init(void)
{
        return register_asymmetric_key_parser(&x509_key_parser);
}

static void __exit x509_key_exit(void)
{
        unregister_asymmetric_key_parser(&x509_key_parser);
}

module_init(x509_key_init);
module_exit(x509_key_exit);

MODULE_DESCRIPTION("X.509 certificate parser");
MODULE_LICENSE("GPL");