x509_public_key.c

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/* Instantiate a public key crypto key from an X.509 Certificate
 *
 * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells ([email protected])
 *
 * 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);