library/ssl_cookie.c

/*
 *  DTLS cookie callbacks implementation
 *
 *  Copyright The Mbed TLS Contributors
 *  SPDX-License-Identifier: Apache-2.0
 *
 *  Licensed under the Apache License, Version 2.0 (the "License"); you may
 *  not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *  http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
/*
 * These session callbacks use a simple chained list
 * to store and retrieve the session information.
 */

#include "common.h"

#if defined(MBEDTLS_SSL_COOKIE_C)

#    if defined(MBEDTLS_PLATFORM_C)
#        include "mbedtls/platform.h"
#    else
#        define mbedtls_calloc calloc
#        define mbedtls_free   free
#    endif

#    include "mbedtls/ssl_cookie.h"
#    include "ssl_misc.h"
#    include "mbedtls/error.h"
#    include "mbedtls/platform_util.h"

#    include <string.h>

/*
 * If DTLS is in use, then at least one of SHA-1, SHA-256, SHA-512 is
 * available. Try SHA-256 first, 512 wastes resources
 */
#    if defined(MBEDTLS_SHA224_C)
#        define COOKIE_MD        MBEDTLS_MD_SHA224
#        define COOKIE_MD_OUTLEN 32
#        define COOKIE_HMAC_LEN  28
#    elif defined(MBEDTLS_SHA384_C)
#        define COOKIE_MD        MBEDTLS_MD_SHA384
#        define COOKIE_MD_OUTLEN 48
#        define COOKIE_HMAC_LEN  28
#    elif defined(MBEDTLS_SHA1_C)
#        define COOKIE_MD        MBEDTLS_MD_SHA1
#        define COOKIE_MD_OUTLEN 20
#        define COOKIE_HMAC_LEN  20
#    else
#        error "DTLS hello verify needs SHA-1 or SHA-2"
#    endif

/*
 * Cookies are formed of a 4-bytes timestamp (or serial number) and
 * an HMAC of timestemp and client ID.
 */
#    define COOKIE_LEN (4 + COOKIE_HMAC_LEN)

void mbedtls_ssl_cookie_init(mbedtls_ssl_cookie_ctx *ctx)
{
    mbedtls_md_init(&ctx->hmac_ctx);
#    if !defined(MBEDTLS_HAVE_TIME)
    ctx->serial = 0;
#    endif
    ctx->timeout = MBEDTLS_SSL_COOKIE_TIMEOUT;

#    if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_init(&ctx->mutex);
#    endif
}

void mbedtls_ssl_cookie_set_timeout(mbedtls_ssl_cookie_ctx *ctx,
                                    unsigned long delay)
{
    ctx->timeout = delay;
}

void mbedtls_ssl_cookie_free(mbedtls_ssl_cookie_ctx *ctx)
{
    mbedtls_md_free(&ctx->hmac_ctx);

#    if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_free(&ctx->mutex);
#    endif

    mbedtls_platform_zeroize(ctx, sizeof(mbedtls_ssl_cookie_ctx));
}

int mbedtls_ssl_cookie_setup(mbedtls_ssl_cookie_ctx *ctx,
                             int (*f_rng)(void *, unsigned char *, size_t),
                             void *p_rng)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    unsigned char key[COOKIE_MD_OUTLEN];

    if ((ret = f_rng(p_rng, key, sizeof(key))) != 0)
        return ret;

    ret = mbedtls_md_setup(&ctx->hmac_ctx, mbedtls_md_info_from_type(COOKIE_MD),
                           1);
    if (ret != 0)
        return ret;

    ret = mbedtls_md_hmac_starts(&ctx->hmac_ctx, key, sizeof(key));
    if (ret != 0)
        return ret;

    mbedtls_platform_zeroize(key, sizeof(key));

    return 0;
}

/*
 * Generate the HMAC part of a cookie
 */
static int ssl_cookie_hmac(mbedtls_md_context_t *hmac_ctx,
                           const unsigned char time[4],
                           unsigned char **p,
                           unsigned char *end,
                           const unsigned char *cli_id,
                           size_t cli_id_len)
{
    unsigned char hmac_out[COOKIE_MD_OUTLEN];

    MBEDTLS_SSL_CHK_BUF_PTR(*p, end, COOKIE_HMAC_LEN);

    if (mbedtls_md_hmac_reset(hmac_ctx) != 0 ||
        mbedtls_md_hmac_update(hmac_ctx, time, 4) != 0 ||
        mbedtls_md_hmac_update(hmac_ctx, cli_id, cli_id_len) != 0 ||
        mbedtls_md_hmac_finish(hmac_ctx, hmac_out) != 0) {
        return MBEDTLS_ERR_SSL_INTERNAL_ERROR;
    }

    memcpy(*p, hmac_out, COOKIE_HMAC_LEN);
    *p += COOKIE_HMAC_LEN;

    return 0;
}

/*
 * Generate cookie for DTLS ClientHello verification
 */
int mbedtls_ssl_cookie_write(void *p_ctx,
                             unsigned char **p,
                             unsigned char *end,
                             const unsigned char *cli_id,
                             size_t cli_id_len)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
    mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *)p_ctx;
    unsigned long t;

    if (ctx == NULL || cli_id == NULL)
        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;

    MBEDTLS_SSL_CHK_BUF_PTR(*p, end, COOKIE_LEN);

#    if defined(MBEDTLS_HAVE_TIME)
    t = (unsigned long)mbedtls_time(NULL);
#    else
    t = ctx->serial++;
#    endif

    (*p)[0] = (unsigned char)(t >> 24);
    (*p)[1] = (unsigned char)(t >> 16);
    (*p)[2] = (unsigned char)(t >> 8);
    (*p)[3] = (unsigned char)(t);
    *p += 4;

#    if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0)
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret);
#    endif

    ret = ssl_cookie_hmac(&ctx->hmac_ctx, *p - 4, p, end, cli_id, cli_id_len);

#    if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0)
        return (MBEDTLS_ERROR_ADD(MBEDTLS_ERR_SSL_INTERNAL_ERROR,
                                  MBEDTLS_ERR_THREADING_MUTEX_ERROR));
#    endif

    return ret;
}

/*
 * Check a cookie
 */
int mbedtls_ssl_cookie_check(void *p_ctx,
                             const unsigned char *cookie,
                             size_t cookie_len,
                             const unsigned char *cli_id,
                             size_t cli_id_len)
{
    unsigned char ref_hmac[COOKIE_HMAC_LEN];
    int ret = 0;
    unsigned char *p = ref_hmac;
    mbedtls_ssl_cookie_ctx *ctx = (mbedtls_ssl_cookie_ctx *)p_ctx;
    unsigned long cur_time, cookie_time;

    if (ctx == NULL || cli_id == NULL)
        return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;

    if (cookie_len != COOKIE_LEN)
        return -1;

#    if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&ctx->mutex)) != 0)
        return MBEDTLS_ERROR_ADD(MBEDTLS_ERR_SSL_INTERNAL_ERROR, ret);
#    endif

    if (ssl_cookie_hmac(&ctx->hmac_ctx, cookie, &p, p + sizeof(ref_hmac),
                        cli_id, cli_id_len) != 0)
        ret = -1;

#    if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&ctx->mutex) != 0)
        return (MBEDTLS_ERROR_ADD(MBEDTLS_ERR_SSL_INTERNAL_ERROR,
                                  MBEDTLS_ERR_THREADING_MUTEX_ERROR));
#    endif

    if (ret != 0)
        return ret;

    if (mbedtls_ssl_safer_memcmp(cookie + 4, ref_hmac, sizeof(ref_hmac)) != 0)
        return -1;

#    if defined(MBEDTLS_HAVE_TIME)
    cur_time = (unsigned long)mbedtls_time(NULL);
#    else
    cur_time = ctx->serial;
#    endif

    cookie_time = ((unsigned long)cookie[0] << 24) |
                  ((unsigned long)cookie[1] << 16) |
                  ((unsigned long)cookie[2] << 8) | ((unsigned long)cookie[3]);

    if (ctx->timeout != 0 && cur_time - cookie_time > ctx->timeout)
        return -1;

    return 0;
}
#endif /* MBEDTLS_SSL_COOKIE_C */