/* 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 <linux/err.h>
#include <linux/mpi.h>
#include <linux/asn1_decoder.h>
#include <keys/asymmetric-subtype.h>
#include <keys/asymmetric-parser.h>
#include <crypto/hash.h>
#include "asymmetric_keys.h"
#include "public_key.h"
#include "x509_parser.h"

static const
struct public_key_algorithm *x509_public_key_algorithms[PKEY_ALGO__LAST] = {
        [PKEY_ALGO_DSA]         = NULL,
#if defined(CONFIG_PUBLIC_KEY_ALGO_RSA) || \
        defined(CONFIG_PUBLIC_KEY_ALGO_RSA_MODULE)
        [PKEY_ALGO_RSA]         = &RSA_public_key_algorithm,
#endif
};

/*
 * Check the signature on a certificate using the provided public key
 */
static int x509_check_signature(const struct public_key *pub,
                                const struct x509_certificate *cert)
{
        struct public_key_signature *sig;
        struct crypto_shash *tfm;
        struct shash_desc *desc;
        size_t digest_size, desc_size;
        int ret;

        pr_devel("==>%s()\n", __func__);
        
        /* Allocate the hashing algorithm we're going to need and find out how
         * big the hash operational data will be.
         */
        tfm = crypto_alloc_shash(pkey_hash_algo[cert->sig_hash_algo], 0, 0);
        if (IS_ERR(tfm))
                return (PTR_ERR(tfm) == -ENOENT) ? -ENOPKG : 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 our
         * context data.
         */
        ret = -ENOMEM;
        sig = kzalloc(sizeof(*sig) + desc_size + digest_size, GFP_KERNEL);
        if (!sig)
                goto error_no_sig;

        sig->pkey_hash_algo     = cert->sig_hash_algo;
        sig->digest             = (u8 *)sig + sizeof(*sig) + desc_size;
        sig->digest_size        = digest_size;

        desc = (void *)sig + sizeof(*sig);
        desc->tfm       = tfm;
        desc->flags     = CRYPTO_TFM_REQ_MAY_SLEEP;

        ret = crypto_shash_init(desc);
        if (ret < 0)
                goto error;

        ret = -ENOMEM;
        sig->rsa.s = mpi_read_raw_data(cert->sig, cert->sig_size);
        if (!sig->rsa.s)
                goto error;

        ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, sig->digest);
        if (ret < 0)
                goto error_mpi;

        ret = pub->algo->verify_signature(pub, sig);

        pr_debug("Cert Verification: %d\n", ret);

error_mpi:
        mpi_free(sig->rsa.s);
error:
        kfree(sig);
error_no_sig:
        crypto_free_shash(tfm);

        pr_devel("<==%s() = %d\n", __func__, ret);
        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 x509_certificate *cert;
        struct tm now;
        size_t srlen, sulen;
        char *desc = NULL;
        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);
        pr_devel("Cert Key Algo: %s\n", pkey_algo[cert->pkey_algo]);
        pr_devel("Cert Valid From: %04ld-%02d-%02d %02d:%02d:%02d\n",
                 cert->valid_from.tm_year + 1900, cert->valid_from.tm_mon + 1,
                 cert->valid_from.tm_mday, cert->valid_from.tm_hour,
                 cert->valid_from.tm_min,  cert->valid_from.tm_sec);
        pr_devel("Cert Valid To: %04ld-%02d-%02d %02d:%02d:%02d\n",
                 cert->valid_to.tm_year + 1900, cert->valid_to.tm_mon + 1,
                 cert->valid_to.tm_mday, cert->valid_to.tm_hour,
                 cert->valid_to.tm_min,  cert->valid_to.tm_sec);
        pr_devel("Cert Signature: %s + %s\n",
                 pkey_algo[cert->sig_pkey_algo],
                 pkey_hash_algo[cert->sig_hash_algo]);

        if (!cert->fingerprint || !cert->authority) {
                pr_warn("Cert for '%s' must have SubjKeyId and AuthKeyId extensions\n",
                        cert->subject);
                ret = -EKEYREJECTED;
                goto error_free_cert;
        }

        time_to_tm(CURRENT_TIME.tv_sec, 0, &now);
        pr_devel("Now: %04ld-%02d-%02d %02d:%02d:%02d\n",
                 now.tm_year + 1900, now.tm_mon + 1, now.tm_mday,
                 now.tm_hour, now.tm_min,  now.tm_sec);
        if (now.tm_year < cert->valid_from.tm_year ||
            (now.tm_year == cert->valid_from.tm_year &&
             (now.tm_mon < cert->valid_from.tm_mon ||
              (now.tm_mon == cert->valid_from.tm_mon &&
               (now.tm_mday < cert->valid_from.tm_mday ||
                (now.tm_mday == cert->valid_from.tm_mday &&
                 (now.tm_hour < cert->valid_from.tm_hour ||
                  (now.tm_hour == cert->valid_from.tm_hour &&
                   (now.tm_min < cert->valid_from.tm_min ||
                    (now.tm_min == cert->valid_from.tm_min &&
                     (now.tm_sec < cert->valid_from.tm_sec
                      ))))))))))) {
                pr_warn("Cert %s is not yet valid\n", cert->fingerprint);
                ret = -EKEYREJECTED;
                goto error_free_cert;
        }
        if (now.tm_year > cert->valid_to.tm_year ||
            (now.tm_year == cert->valid_to.tm_year &&
             (now.tm_mon > cert->valid_to.tm_mon ||
              (now.tm_mon == cert->valid_to.tm_mon &&
               (now.tm_mday > cert->valid_to.tm_mday ||
                (now.tm_mday == cert->valid_to.tm_mday &&
                 (now.tm_hour > cert->valid_to.tm_hour ||
                  (now.tm_hour == cert->valid_to.tm_hour &&
                   (now.tm_min > cert->valid_to.tm_min ||
                    (now.tm_min == cert->valid_to.tm_min &&
                     (now.tm_sec > cert->valid_to.tm_sec
                      ))))))))))) {
                pr_warn("Cert %s has expired\n", cert->fingerprint);
                ret = -EKEYEXPIRED;
                goto error_free_cert;
        }

        cert->pub->algo = x509_public_key_algorithms[cert->pkey_algo];
        cert->pub->id_type = PKEY_ID_X509;

        /* Check the signature on the key */
        if (strcmp(cert->fingerprint, cert->authority) == 0) {
                ret = x509_check_signature(cert->pub, cert);
                if (ret < 0)
                        goto error_free_cert;
        }

        /* Propose a description */
        sulen = strlen(cert->subject);
        srlen = strlen(cert->fingerprint);
        ret = -ENOMEM;
        desc = kmalloc(sulen + 2 + srlen + 1, GFP_KERNEL);
        if (!desc)
                goto error_free_cert;
        memcpy(desc, cert->subject, sulen);
        desc[sulen] = ':';
        desc[sulen + 1] = ' ';
        memcpy(desc + sulen + 2, cert->fingerprint, srlen);
        desc[sulen + 2 + srlen] = 0;

        /* We're pinning the module by being linked against it */
        __module_get(public_key_subtype.owner);
        prep->type_data[0] = &public_key_subtype;
        prep->type_data[1] = cert->fingerprint;
        prep->payload = cert->pub;
        prep->description = desc;
        prep->quotalen = 100;

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

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);