mbedtls/library/ssl_cache.c

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/*
* SSL session cache implementation
*
* Copyright The Mbed TLS Contributors
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* SPDX-License-Identifier: Apache-2.0
*
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* 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
*
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* http://www.apache.org/licenses/LICENSE-2.0
*
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* 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)
#if defined(MBEDTLS_PLATFORM_C)
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#include "mbedtls/platform.h"
#else
#include <stdlib.h>
#define mbedtls_calloc calloc
#define mbedtls_free free
#endif
#include "mbedtls/ssl_cache.h"
#include "ssl_misc.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;
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#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_init( &cache->mutex );
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#endif
}
static int ssl_cache_find_entry( mbedtls_ssl_cache_context *cache,
unsigned char const *session_id,
size_t session_id_len,
mbedtls_ssl_cache_entry **dst )
{
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int ret = 1;
#if defined(MBEDTLS_HAVE_TIME)
mbedtls_time_t t = mbedtls_time( NULL );
#endif
mbedtls_ssl_cache_entry *cur;
for( cur = cache->chain; cur != NULL; cur = cur->next )
{
#if defined(MBEDTLS_HAVE_TIME)
if( cache->timeout != 0 &&
(int) ( t - cur->timestamp ) > cache->timeout )
continue;
#endif
if( session_id_len != cur->session_id_len ||
memcmp( session_id, cur->session_id,
cur->session_id_len ) != 0 )
{
continue;
}
break;
}
if( cur != NULL )
{
*dst = cur;
ret = 0;
}
return( ret );
}
int mbedtls_ssl_cache_get( void *data,
unsigned char const *session_id,
size_t session_id_len,
mbedtls_ssl_session *session )
{
int ret = 1;
mbedtls_ssl_cache_context *cache = (mbedtls_ssl_cache_context *) data;
mbedtls_ssl_cache_entry *entry;
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_lock( &cache->mutex ) != 0 )
return( 1 );
#endif
ret = ssl_cache_find_entry( cache, session_id, session_id_len, &entry );
if( ret != 0 )
goto exit;
ret = mbedtls_ssl_session_load( session,
entry->session,
entry->session_len );
if( ret != 0 )
goto exit;
ret = 0;
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exit:
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_unlock( &cache->mutex ) != 0 )
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ret = 1;
#endif
return( ret );
}
static int ssl_cache_pick_writing_slot( mbedtls_ssl_cache_context *cache,
unsigned char const *session_id,
size_t session_id_len,
mbedtls_ssl_cache_entry **dst )
{
#if defined(MBEDTLS_HAVE_TIME)
mbedtls_time_t t = mbedtls_time( NULL ), oldest = 0;
#endif /* MBEDTLS_HAVE_TIME */
mbedtls_ssl_cache_entry *old = NULL;
int count = 0;
mbedtls_ssl_cache_entry *cur, *prv;
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cur = cache->chain;
prv = NULL;
/* Check 1: Is there already an entry with the given session ID?
*
* If yes, overwrite it.
*
* If not, `count` will hold the size of the session cache
* at the end of this loop, and `prv` will point to the last
* entry, both of which will be used later. */
while( cur != NULL )
{
count++;
if( session_id_len == cur->session_id_len &&
memcmp( session_id, cur->session_id, cur->session_id_len ) == 0 )
{
goto found;
}
prv = cur;
cur = cur->next;
}
/* Check 2: Is there an outdated entry in the cache?
*
* If so, overwrite it.
*
* If not, remember the oldest entry in `old` for later.
*/
#if defined(MBEDTLS_HAVE_TIME)
while( cur != NULL )
{
if( cache->timeout != 0 &&
(int) ( t - cur->timestamp ) > cache->timeout )
{
goto found;
}
if( oldest == 0 || cur->timestamp < oldest )
{
oldest = cur->timestamp;
old = cur;
}
prv = cur;
cur = cur->next;
}
#endif /* MBEDTLS_HAVE_TIME */
/* Check 3: Is there free space in the cache? */
if( count < cache->max_entries )
{
/* Create new entry */
cur = mbedtls_calloc( 1, sizeof(mbedtls_ssl_cache_entry) );
if( cur == NULL )
return( 1 );
/* Append to the end of the linked list. */
if( prv == NULL )
cache->chain = cur;
else
prv->next = cur;
goto found;
}
/* Last resort: The cache is full and doesn't contain any outdated
* elements. In this case, we evict the oldest one, judged by timestamp
* (if present) or cache-order. */
#if defined(MBEDTLS_HAVE_TIME)
if( old == NULL )
{
/* This should only happen on an ill-configured cache
* with max_entries == 0. */
return( 1 );
}
#else /* MBEDTLS_HAVE_TIME */
/* Reuse first entry in chain, but move to last place. */
if( cache->chain == NULL )
return( 1 );
old = cache->chain;
cache->chain = old->next;
cur->next = NULL;
prv->next = old;
#endif /* MBEDTLS_HAVE_TIME */
/* Now `old` points to the oldest entry to be overwritten. */
cur = old;
found:
#if defined(MBEDTLS_HAVE_TIME)
cur->timestamp = t;
#endif
/* If we're reusing an entry, free it first. */
if( cur->session != NULL )
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{
mbedtls_free( cur->session );
cur->session = NULL;
cur->session_len = 0;
memset( cur->session_id, 0, sizeof( cur->session_id ) );
cur->session_id_len = 0;
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}
*dst = cur;
return( 0 );
}
int mbedtls_ssl_cache_set( void *data,
unsigned char const *session_id,
size_t session_id_len,
const mbedtls_ssl_session *session )
{
int ret = 1;
mbedtls_ssl_cache_context *cache = (mbedtls_ssl_cache_context *) data;
mbedtls_ssl_cache_entry *cur;
size_t session_serialized_len;
unsigned char *session_serialized = NULL;
#if defined(MBEDTLS_THREADING_C)
if( ( ret = mbedtls_mutex_lock( &cache->mutex ) ) != 0 )
return( ret );
#endif
ret = ssl_cache_pick_writing_slot( cache,
session_id, session_id_len,
&cur );
if( ret != 0 )
goto exit;
/* Check how much space we need to serialize the session
* and allocate a sufficiently large buffer. */
ret = mbedtls_ssl_session_save( session, NULL, 0, &session_serialized_len );
if( ret != MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL )
{
ret = 1;
goto exit;
}
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session_serialized = mbedtls_calloc( 1, session_serialized_len );
if( session_serialized == NULL )
{
ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
goto exit;
}
/* Now serialize the session into the allocated buffer. */
ret = mbedtls_ssl_session_save( session,
session_serialized,
session_serialized_len,
&session_serialized_len );
if( ret != 0 )
goto exit;
if( session_id_len > sizeof( cur->session_id ) )
{
ret = 1;
goto exit;
}
cur->session_id_len = session_id_len;
memcpy( cur->session_id, session_id, session_id_len );
cur->session = session_serialized;
cur->session_len = session_serialized_len;
session_serialized = NULL;
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ret = 0;
exit:
#if defined(MBEDTLS_THREADING_C)
if( mbedtls_mutex_unlock( &cache->mutex ) != 0 )
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ret = 1;
#endif
if( session_serialized != NULL )
mbedtls_platform_zeroize( session_serialized, session_serialized_len );
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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_free( prv->session );
mbedtls_free( prv );
}
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#if defined(MBEDTLS_THREADING_C)
mbedtls_mutex_free( &cache->mutex );
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#endif
cache->chain = NULL;
}
#endif /* MBEDTLS_SSL_CACHE_C */