/* 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"

/*
 * 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 public_key_signature *sig = cert->sig;
        struct crypto_shash *tfm;
        struct shash_desc *desc;
        size_t desc_size;
        int ret;

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

        if (!cert->pub->pkey_algo)
                cert->unsupported_key = true;

        if (!sig->pkey_algo)
                cert->unsupported_sig = true;

        /* We check the hash if we can - even if we can't then verify it */
        if (!sig->hash_algo) {
                cert->unsupported_sig = true;
                return 0;
        }

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

        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(sig->hash_algo, 0, 0);
        if (IS_ERR(tfm)) {
                if (PTR_ERR(tfm) == -ENOENT) {
                        cert->unsupported_sig = true;
                        return 0;
                }
                return PTR_ERR(tfm);
        }

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

        ret = -ENOMEM;
        sig->digest = kmalloc(sig->digest_size, GFP_KERNEL);
        if (!sig->digest)
                goto error;

        desc = kzalloc(desc_size, GFP_KERNEL);
        if (!desc)
                goto error;

        desc->tfm = tfm;
        desc->flags = CRYPTO_TFM_REQ_MAY_SLEEP;

        ret = crypto_shash_init(desc);
        if (ret < 0)
                goto error_2;
        might_sleep();
        ret = crypto_shash_finup(desc, cert->tbs, cert->tbs_size, sig->digest);

error_2:
        kfree(desc);
error:
        crypto_free_shash(tfm);
        pr_devel("<==%s() = %d\n", __func__, ret);
        return ret;
}

/*
 * Check for self-signedness in an X.509 cert and if found, check the signature
 * immediately if we can.
 */
int x509_check_for_self_signed(struct x509_certificate *cert)
{
        int ret = 0;

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

        if (cert->raw_subject_size != cert->raw_issuer_size ||
            memcmp(cert->raw_subject, cert->raw_issuer,
                   cert->raw_issuer_size) != 0)
                goto not_self_signed;

        if (cert->sig->auth_ids[0] || cert->sig->auth_ids[1]) {
                /* If the AKID is present it may have one or two parts.  If
                 * both are supplied, both must match.
                 */
                bool a = asymmetric_key_id_same(cert->skid, cert->sig->auth_ids[1]);
                bool b = asymmetric_key_id_same(cert->id, cert->sig->auth_ids[0]);

                if (!a && !b)
                        goto not_self_signed;

                ret = -EKEYREJECTED;
                if (((a && !b) || (b && !a)) &&
                    cert->sig->auth_ids[0] && cert->sig->auth_ids[1])
                        goto out;
        }

        ret = -EKEYREJECTED;
        if (cert->pub->pkey_algo != cert->sig->pkey_algo)
                goto out;

        ret = public_key_verify_signature(cert->pub, cert->sig);
        if (ret < 0) {
                if (ret == -ENOPKG) {
                        cert->unsupported_sig = true;
                        ret = 0;
                }
                goto out;
        }

        pr_devel("Cert Self-signature verified");
        cert->self_signed = true;

out:
        pr_devel("<==%s() = %d\n", __func__, ret);
        return ret;

not_self_signed:
        pr_devel("<==%s() = 0 [not]\n", __func__);
        return 0;
}

/*
 * 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->unsupported_key) {
                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);

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

        if (cert->unsupported_sig) {
                public_key_signature_free(cert->sig);
                cert->sig = NULL;
        } else {
                pr_devel("Cert Signature: %s + %s\n",
                         cert->sig->pkey_algo, cert->sig->hash_algo);
        }

        /* 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->payload.data[asym_auth] = cert->sig;
        prep->description = desc;
        prep->quotalen = 100;

        /* We've finished with the certificate */
        cert->pub = NULL;
        cert->id = NULL;
        cert->skid = NULL;
        cert->sig = 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");