library/ssl_cache.c

/*
 *  SSL session cache 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_CACHE_C)

#include "mbedtls/platform.h"
#include "mbedtls/error.h"

#include "mbedtls/ssl_cache.h"
#include "mbedtls/ssl_internal.h"

#include <string.h>

void mbedtls_ssl_cache_init(mbedtls_ssl_cache_context *cache)
{
    memset(cache, 0, sizeof(mbedtls_ssl_cache_context));

    cache->timeout = MBEDTLS_SSL_CACHE_DEFAULT_TIMEOUT;
    cache->max_entries = MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES;

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

int mbedtls_ssl_cache_get(void *data, mbedtls_ssl_session *session)
{
    int ret = MBEDTLS_ERR_SSL_CACHE_ENTRY_NOT_FOUND;
#if defined(MBEDTLS_HAVE_TIME)
    mbedtls_time_t t = mbedtls_time(NULL);
#endif
    mbedtls_ssl_cache_context *cache = (mbedtls_ssl_cache_context *) data;
    mbedtls_ssl_cache_entry *cur, *entry;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&cache->mutex)) != 0) {
        return ret;
    }
#endif

    cur = cache->chain;
    entry = NULL;

    while (cur != NULL) {
        entry = cur;
        cur = cur->next;

#if defined(MBEDTLS_HAVE_TIME)
        if (cache->timeout != 0 &&
            (int) (t - entry->timestamp) > cache->timeout) {
            continue;
        }
#endif

        if (session->id_len != entry->session.id_len ||
            memcmp(session->id, entry->session.id,
                   entry->session.id_len) != 0) {
            continue;
        }

        ret = mbedtls_ssl_session_copy(session, &entry->session);
        if (ret != 0) {
            goto exit;
        }

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
        defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        /*
         * Restore peer certificate (without rest of the original chain)
         */
        if (entry->peer_cert.p != NULL) {
            /* `session->peer_cert` is NULL after the call to
             * mbedtls_ssl_session_copy(), because cache entries
             * have the `peer_cert` field set to NULL. */

            if ((session->peer_cert = mbedtls_calloc(1,
                                                     sizeof(mbedtls_x509_crt))) == NULL) {
                ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
                goto exit;
            }

            mbedtls_x509_crt_init(session->peer_cert);
            if ((ret = mbedtls_x509_crt_parse(session->peer_cert, entry->peer_cert.p,
                                              entry->peer_cert.len)) != 0) {
                mbedtls_free(session->peer_cert);
                session->peer_cert = NULL;
                goto exit;
            }
        }
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

        ret = 0;
        goto exit;
    }

exit:
#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&cache->mutex) != 0) {
        ret = MBEDTLS_ERR_THREADING_MUTEX_ERROR;
    }
#endif

    return ret;
}

int mbedtls_ssl_cache_set(void *data, const mbedtls_ssl_session *session)
{
    int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
#if defined(MBEDTLS_HAVE_TIME)
    mbedtls_time_t t = mbedtls_time(NULL), oldest = 0;
    mbedtls_ssl_cache_entry *old = NULL;
#endif
    mbedtls_ssl_cache_context *cache = (mbedtls_ssl_cache_context *) data;
    mbedtls_ssl_cache_entry *cur, *prv;
    int count = 0;

#if defined(MBEDTLS_THREADING_C)
    if ((ret = mbedtls_mutex_lock(&cache->mutex)) != 0) {
        return ret;
    }
#endif

    cur = cache->chain;
    prv = NULL;

    while (cur != NULL) {
        count++;

#if defined(MBEDTLS_HAVE_TIME)
        if (cache->timeout != 0 &&
            (int) (t - cur->timestamp) > cache->timeout) {
            cur->timestamp = t;
            break; /* expired, reuse this slot, update timestamp */
        }
#endif

        if (memcmp(session->id, cur->session.id, cur->session.id_len) == 0) {
            break; /* client reconnected, keep timestamp for session id */

        }
#if defined(MBEDTLS_HAVE_TIME)
        if (oldest == 0 || cur->timestamp < oldest) {
            oldest = cur->timestamp;
            old = cur;
        }
#endif

        prv = cur;
        cur = cur->next;
    }

    if (cur == NULL) {
#if defined(MBEDTLS_HAVE_TIME)
        /*
         * Reuse oldest entry if max_entries reached
         */
        if (count >= cache->max_entries) {
            if (old == NULL) {
                /* This should only happen on an ill-configured cache
                 * with max_entries == 0. */
                ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
                goto exit;
            }

            cur = old;
        }
#else /* MBEDTLS_HAVE_TIME */
        /*
         * Reuse first entry in chain if max_entries reached,
         * but move to last place
         */
        if (count >= cache->max_entries) {
            if (cache->chain == NULL) {
                ret = MBEDTLS_ERR_SSL_INTERNAL_ERROR;
                goto exit;
            }

            cur = cache->chain;
            cache->chain = cur->next;
            cur->next = NULL;
            prv->next = cur;
        }
#endif /* MBEDTLS_HAVE_TIME */
        else {
            /*
             * max_entries not reached, create new entry
             */
            cur = mbedtls_calloc(1, sizeof(mbedtls_ssl_cache_entry));
            if (cur == NULL) {
                ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
                goto exit;
            }

            if (prv == NULL) {
                cache->chain = cur;
            } else {
                prv->next = cur;
            }
        }

#if defined(MBEDTLS_HAVE_TIME)
        cur->timestamp = t;
#endif
    }

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    /*
     * If we're reusing an entry, free its certificate first
     */
    if (cur->peer_cert.p != NULL) {
        mbedtls_free(cur->peer_cert.p);
        memset(&cur->peer_cert, 0, sizeof(mbedtls_x509_buf));
    }
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    /* Copy the entire session; this temporarily makes a copy of the
     * X.509 CRT structure even though we only want to store the raw CRT.
     * This inefficiency will go away as soon as we implement on-demand
     * parsing of CRTs, in which case there's no need for the `peer_cert`
     * field anymore in the first place, and we're done after this call. */
    ret = mbedtls_ssl_session_copy(&cur->session, session);
    if (ret != 0) {
        goto exit;
    }

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
    defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
    /* If present, free the X.509 structure and only store the raw CRT data. */
    if (cur->session.peer_cert != NULL) {
        cur->peer_cert.p =
            mbedtls_calloc(1, cur->session.peer_cert->raw.len);
        if (cur->peer_cert.p == NULL) {
            ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
            goto exit;
        }

        memcpy(cur->peer_cert.p,
               cur->session.peer_cert->raw.p,
               cur->session.peer_cert->raw.len);
        cur->peer_cert.len = session->peer_cert->raw.len;

        mbedtls_x509_crt_free(cur->session.peer_cert);
        mbedtls_free(cur->session.peer_cert);
        cur->session.peer_cert = NULL;
    }
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

    ret = 0;

exit:
#if defined(MBEDTLS_THREADING_C)
    if (mbedtls_mutex_unlock(&cache->mutex) != 0) {
        ret = MBEDTLS_ERR_THREADING_MUTEX_ERROR;
    }
#endif

    return ret;
}

#if defined(MBEDTLS_HAVE_TIME)
void mbedtls_ssl_cache_set_timeout(mbedtls_ssl_cache_context *cache, int timeout)
{
    if (timeout < 0) {
        timeout = 0;
    }

    cache->timeout = timeout;
}
#endif /* MBEDTLS_HAVE_TIME */

void mbedtls_ssl_cache_set_max_entries(mbedtls_ssl_cache_context *cache, int max)
{
    if (max < 0) {
        max = 0;
    }

    cache->max_entries = max;
}

void mbedtls_ssl_cache_free(mbedtls_ssl_cache_context *cache)
{
    mbedtls_ssl_cache_entry *cur, *prv;

    cur = cache->chain;

    while (cur != NULL) {
        prv = cur;
        cur = cur->next;

        mbedtls_ssl_session_free(&prv->session);

#if defined(MBEDTLS_X509_CRT_PARSE_C) && \
        defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
        mbedtls_free(prv->peer_cert.p);
#endif /* MBEDTLS_X509_CRT_PARSE_C && MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */

        mbedtls_free(prv);
    }

#if defined(MBEDTLS_THREADING_C)
    mbedtls_mutex_free(&cache->mutex);
#endif
    cache->chain = NULL;
}

#endif /* MBEDTLS_SSL_CACHE_C */