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Implement future record buffering

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This commit implements the buffering of a record from the next epoch.

- The buffering substructure of mbedtls_ssl_handshake_params
  gets another field to hold a raw record (incl. header) from
  a future epoch.
- If ssl_parse_record_header() sees a record from the next epoch,
  it signals that it might be suitable for buffering by returning
  MBEDTLS_ERR_SSL_EARLY_MESSAGE.
- If ssl_get_next_record() finds this error code, it passes control
  to ssl_buffer_future_record() which may or may not decide to buffer
  the record; it does so if
  - a handshake is in progress,
  - the record is a handshake record
  - no record has already been buffered.
  If these conditions are met, the record is backed up in the
  aforementioned buffering substructure.
- If the current datagram is fully processed, ssl_load_buffered_record()
  is called to check if a record has been buffered, and if yes,
  if by now the its epoch is the current one; if yes, it copies
  the record into the (empty! otherwise, ssl_load_buffered_record()
  wouldn't have been called) input buffer.
This commit is contained in:
Hanno Becker 2018-08-16 14:56:31 +01:00
parent e38422107e
commit 5f066e7aac
2 changed files with 152 additions and 3 deletions
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7
include/mbedtls/ssl_internal.h
View file

@ -322,6 +322,13 @@ struct mbedtls_ssl_handshake_params
unsigned char *data;
} hs[MBEDTLS_SSL_MAX_BUFFERED_HS];
struct
{
unsigned char *data;
size_t len;
unsigned epoch;
} future_record;
} buffering;
#endif /* MBEDTLS_SSL_PROTO_DTLS */

148
library/ssl_tls.c
View file

@ -4097,8 +4097,17 @@ static int ssl_parse_record_header( mbedtls_ssl_context *ssl )
}
else
#endif /* MBEDTLS_SSL_DTLS_CLIENT_PORT_REUSE && MBEDTLS_SSL_SRV_C */
{
/* Consider buffering the record. */
if( rec_epoch == (unsigned int) ssl->in_epoch + 1 )
{
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Consider record for buffering" ) );
return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
}
return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
}
}
#if defined(MBEDTLS_SSL_DTLS_ANTI_REPLAY)
/* Replay detection only works for the current epoch */
@ -4254,7 +4263,9 @@ static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl );
#if defined(MBEDTLS_SSL_PROTO_DTLS)
static int ssl_load_buffered_message( mbedtls_ssl_context *ssl );
static int ssl_load_buffered_record( mbedtls_ssl_context *ssl );
static int ssl_buffer_message( mbedtls_ssl_context *ssl );
static int ssl_buffer_future_record( mbedtls_ssl_context *ssl );
static int ssl_another_record_in_datagram( mbedtls_ssl_context *ssl );
#endif /* MBEDTLS_SSL_PROTO_DTLS */
@ -4689,13 +4700,133 @@ static int ssl_record_is_in_progress( mbedtls_ssl_context *ssl )
return( 0 );
}
#if defined(MBEDTLS_SSL_PROTO_DTLS)
static void ssl_free_buffered_record( mbedtls_ssl_context *ssl )
{
mbedtls_ssl_handshake_params * const hs = ssl->handshake;
if( hs == NULL )
return;
mbedtls_free( hs->buffering.future_record.data );
hs->buffering.future_record.data = NULL;
}
static int ssl_load_buffered_record( mbedtls_ssl_context *ssl )
{
mbedtls_ssl_handshake_params * const hs = ssl->handshake;
unsigned char * rec;
size_t rec_len;
unsigned rec_epoch;
if( ssl->conf->transport != MBEDTLS_SSL_TRANSPORT_DATAGRAM )
return( 0 );
if( hs == NULL )
return( 0 );
/* Only consider loading future records if the
* input buffer is empty. */
if( ssl_another_record_in_datagram( ssl ) == 1 )
return( 0 );
rec = hs->buffering.future_record.data;
rec_len = hs->buffering.future_record.len;
rec_epoch = hs->buffering.future_record.epoch;
if( rec == NULL )
return( 0 );
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_load_buffered_record" ) );
if( rec_epoch != ssl->in_epoch )
{
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffered record not from current epoch." ) );
goto exit;
}
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Found buffered record from current epoch - load" ) );
/* Double-check that the record is not too large */
if( rec_len > MBEDTLS_SSL_IN_BUFFER_LEN -
(size_t)( ssl->in_hdr - ssl->in_buf ) )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "should never happen" ) );
return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
}
memcpy( ssl->in_hdr, rec, rec_len );
ssl->in_left = rec_len;
ssl->next_record_offset = 0;
ssl_free_buffered_record( ssl );
exit:
MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_load_buffered_record" ) );
return( 0 );
}
static int ssl_buffer_future_record( mbedtls_ssl_context *ssl )
{
mbedtls_ssl_handshake_params * const hs = ssl->handshake;
size_t const rec_hdr_len = 13;
/* Don't buffer future records outside handshakes. */
if( hs == NULL )
return( 0 );
/* Only buffer handshake records (we are only interested
* in Finished messages). */
if( ssl->in_msgtype != MBEDTLS_SSL_MSG_HANDSHAKE )
return( 0 );
/* Don't buffer more than one future epoch record. */
if( hs->buffering.future_record.data != NULL )
return( 0 );
/* Buffer record */
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Buffer record from epoch %u",
ssl->in_epoch + 1 ) );
MBEDTLS_SSL_DEBUG_BUF( 3, "Buffered record", ssl->in_hdr,
rec_hdr_len + ssl->in_msglen );
/* ssl_parse_record_header() only considers records
* of the next epoch as candidates for buffering. */
hs->buffering.future_record.epoch = ssl->in_epoch + 1;
hs->buffering.future_record.len = rec_hdr_len + ssl->in_msglen;
hs->buffering.future_record.data =
mbedtls_calloc( 1, hs->buffering.future_record.len );
if( hs->buffering.future_record.data == NULL )
{
/* If we run out of RAM trying to buffer a
* record from the next epoch, just ignore. */
return( 0 );
}
memcpy( hs->buffering.future_record.data,
ssl->in_hdr, rec_hdr_len + ssl->in_msglen );
return( 0 );
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */
static int ssl_get_next_record( mbedtls_ssl_context *ssl )
{
int ret;
/*
* Fetch and decode new record
*/
#if defined(MBEDTLS_SSL_PROTO_DTLS)
/* We might have buffered a future record; if so,
* and if the epoch matches now, load it.
* On success, this call will set ssl->in_left to
* the length of the buffered record, so that
* the calls to ssl_fetch_input() below will
* essentially be no-ops. */
ret = ssl_load_buffered_record( ssl );
if( ret != 0 )
return( ret );
#endif /* MBEDTLS_SSL_PROTO_DTLS */
if( ( ret = mbedtls_ssl_fetch_input( ssl, mbedtls_ssl_hdr_len( ssl ) ) ) != 0 )
{
@ -4709,6 +4840,16 @@ static int ssl_get_next_record( mbedtls_ssl_context *ssl )
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
ret != MBEDTLS_ERR_SSL_CLIENT_RECONNECT )
{
if( ret == MBEDTLS_ERR_SSL_EARLY_MESSAGE )
{
ret = ssl_buffer_future_record( ssl );
if( ret != 0 )
return( ret );
/* Fall through to handling of unexpected records */
ret = MBEDTLS_ERR_SSL_UNEXPECTED_RECORD;
}
if( ret == MBEDTLS_ERR_SSL_UNEXPECTED_RECORD )
{
/* Skip unexpected record (but not whole datagram) */
@ -8489,6 +8630,7 @@ void mbedtls_ssl_handshake_free( mbedtls_ssl_context *ssl )
mbedtls_free( handshake->verify_cookie );
ssl_flight_free( handshake->flight );
ssl_buffering_free( ssl );
ssl_free_buffered_record( ssl );
#endif
mbedtls_platform_zeroize( handshake,