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Implement support for remembering CCS messages

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This commit implements support for remembering out-of-order
CCS messages. Specifically, a flag is set whenever a CCS message
is read which remains until the end of a flight, and when a
CCS message is expected and a CCS message has been seen in the
current flight, a synthesized CCS record is created.
This commit is contained in:
Hanno Becker 2018-08-15 15:11:57 +01:00
parent 40f50848fa
commit 2ed6bcc793
2 changed files with 89 additions and 15 deletions
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3
include/mbedtls/ssl_internal.h
View File

@ -307,6 +307,9 @@ struct mbedtls_ssl_handshake_params
resending messages */
unsigned char alt_out_ctr[8]; /*!< Alternative record epoch/counter
for resending messages */
uint8_t seen_ccs; /*!< Indicates if a CCS message has
* been seen in the current flight. */
#endif /* MBEDTLS_SSL_PROTO_DTLS */
/*

97
library/ssl_tls.c
View File

@ -3069,6 +3069,9 @@ void mbedtls_ssl_recv_flight_completed( mbedtls_ssl_context *ssl )
/* The next incoming flight will start with this msg_seq */
ssl->handshake->in_flight_start_seq = ssl->handshake->in_msg_seq;
/* We don't want to remember CCS's across flight boundaries. */
ssl->handshake->seen_ccs = 0;
/* Cancel timer */
ssl_set_timer( ssl, 0 );
@ -4138,15 +4141,6 @@ static int ssl_parse_record_header( mbedtls_ssl_context *ssl )
}
#endif
/* Drop unexpected ChangeCipherSpec messages */
if( ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping unexpected ChangeCipherSpec" ) );
return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
}
/* Drop unexpected ApplicationData records,
* except at the beginning of renegotiations */
if( ssl->in_msgtype == MBEDTLS_SSL_MSG_APPLICATION_DATA &&
@ -4390,16 +4384,75 @@ static int ssl_another_record_in_datagram( mbedtls_ssl_context *ssl )
static int ssl_load_buffered_message( mbedtls_ssl_context *ssl )
{
/* No buffering support so far. */
((void) ssl );
mbedtls_ssl_handshake_params * const hs = ssl->handshake;
int ret = 0;
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_load_buffered_messsage" ) );
if( hs == NULL )
return( -1 );
if( ssl->state == MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC ||
ssl->state == MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
{
/* Check if we have seen a ChangeCipherSpec before.
* If yes, synthesize a CCS record. */
if( ! hs->seen_ccs )
{
MBEDTLS_SSL_DEBUG_MSG( 2, ( "CCS not seen in the current flight" ) );
ret = -1;
goto exit;
}
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Inject buffered CCS message" ) );
ssl->in_msgtype = MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC;
ssl->in_msglen = 1;
ssl->in_msg[0] = 1;
/* As long as they are equal, the exact value doesn't matter. */
ssl->in_left = 0;
ssl->next_record_offset = 0;
hs->seen_ccs = 0;
goto exit;
}
ret = -1;
exit:
MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_load_buffered_message" ) );
return( ret );
}
static int ssl_buffer_message( mbedtls_ssl_context *ssl )
{
/* No buffering support so far. */
((void) ssl );
int ret = 0;
mbedtls_ssl_handshake_params * const hs = ssl->handshake;
if( hs == NULL )
return( 0 );
MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> ssl_buffer_message" ) );
switch( ssl->in_msgtype )
{
case MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC:
MBEDTLS_SSL_DEBUG_MSG( 2, ( "Remember CCS message" ) );
hs->seen_ccs = 1;
break;
case MBEDTLS_SSL_MSG_HANDSHAKE:
/* No support for buffering handshake messages so far. */
break;
default:
break;
}
exit:
MBEDTLS_SSL_DEBUG_MSG( 2, ( "<= ssl_buffer_message" ) );
return( ret );
}
#endif /* MBEDTLS_SSL_PROTO_DTLS */
@ -4649,6 +4702,24 @@ int mbedtls_ssl_handle_message_type( mbedtls_ssl_context *ssl )
}
}
#if defined(MBEDTLS_SSL_PROTO_DTLS)
/* Drop unexpected ChangeCipherSpec messages */
if( ssl->conf->transport == MBEDTLS_SSL_TRANSPORT_DATAGRAM &&
ssl->in_msgtype == MBEDTLS_SSL_MSG_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_CLIENT_CHANGE_CIPHER_SPEC &&
ssl->state != MBEDTLS_SSL_SERVER_CHANGE_CIPHER_SPEC )
{
if( ssl->handshake == NULL )
{
MBEDTLS_SSL_DEBUG_MSG( 1, ( "dropping ChangeCipherSpec outside handshake" ) );
return( MBEDTLS_ERR_SSL_UNEXPECTED_RECORD );
}
MBEDTLS_SSL_DEBUG_MSG( 1, ( "received out-of-order ChangeCipherSpec - remember" ) );
return( MBEDTLS_ERR_SSL_EARLY_MESSAGE );
}
#endif
if( ssl->in_msgtype == MBEDTLS_SSL_MSG_ALERT )
{
if( ssl->in_msglen != 2 )