xrdp/common/trans.h

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/**
* xrdp: A Remote Desktop Protocol server.
*
* Copyright (C) Jay Sorg 2004-2014
*
* 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.
*
* generic transport
*/
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#if !defined(TRANS_H)
#define TRANS_H
#include "arch.h"
#include "parse.h"
#define TRANS_MODE_TCP 1 /* tcp6 if defined, else tcp4 */
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#define TRANS_MODE_UNIX 2
#define TRANS_MODE_VSOCK 3
#define TRANS_MODE_TCP4 4 /* tcp4 only */
#define TRANS_MODE_TCP6 6 /* tcp6 only */
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#define TRANS_TYPE_LISTENER 1
#define TRANS_TYPE_SERVER 2
#define TRANS_TYPE_CLIENT 3
#define TRANS_STATUS_DOWN 0
#define TRANS_STATUS_UP 1
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struct trans; /* forward declaration */
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struct xrdp_tls;
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typedef int (*ttrans_data_in)(struct trans *self);
typedef int (*ttrans_conn_in)(struct trans *self,
struct trans *new_self);
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typedef int (*tis_term)(void);
typedef int (*trans_recv_proc) (struct trans *self, char *ptr, int len);
typedef int (*trans_send_proc) (struct trans *self, const char *data, int len);
typedef int (*trans_can_recv_proc) (struct trans *self, int sck, int millis);
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/* optional source info */
enum xrdp_source
{
XRDP_SOURCE_NONE = 0,
XRDP_SOURCE_CLIENT,
XRDP_SOURCE_SESMAN,
XRDP_SOURCE_CHANSRV,
XRDP_SOURCE_MOD,
XRDP_SOURCE_MAX_COUNT
};
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/*
* @brief Provide flow control mechanism for (primarily) xrdp
*
* There is one of these data structures per-program.
*
* While input is being read from a 'struct trans' and processed, the
* cur_source member is set to the my_source member from the transport.
* During this processing, trans_write_copy() may be called to send output
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* on another struct trans. If this happens, and the output needs to be
* buffered, trans_write_copy() can add the number of bytes generated by
* the input trans to the source field for the cur_source. This allows us to
* see how much output has been buffered for each input source.
*
* When the program assembles 'struct trans' objects to scan for input
* (normally in trans_get_wait_objs()), it is able to see how much buffered
* output is registered for each input. Inputs which have too much buffered
* output owing are skipped, and not considered for input.
*
* This provides a simple means of providing back-pressure on an input
* where the data it is providing is being processed and then sent out on
* a much slower link.
*/
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struct source_info
{
enum xrdp_source cur_source;
int source[XRDP_SOURCE_MAX_COUNT];
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};
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struct trans
{
tbus sck; /* socket handle */
int mode; /* 1 tcp, 2 unix socket, 3 vsock */
int status;
int type1; /* 1 listener 2 server 3 client */
ttrans_data_in trans_data_in;
ttrans_conn_in trans_conn_in;
void *callback_data;
unsigned int header_size;
struct stream *in_s;
struct stream *out_s;
char *listen_filename;
tis_term is_term; /* used to test for exit */
struct stream *wait_s;
int no_stream_init_on_data_in;
int extra_flags; /* user defined */
void *extra_data; /* user defined */
void (*extra_destructor)(struct trans *); /* user defined */
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struct ssl_tls *tls;
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const char *ssl_protocol; /* e.g. TLSv1, TLSv1.1, TLSv1.2, unknown */
const char *cipher_name; /* e.g. AES256-GCM-SHA384 */
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trans_recv_proc trans_recv;
trans_send_proc trans_send;
trans_can_recv_proc trans_can_recv;
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struct source_info *si;
enum xrdp_source my_source;
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};
struct trans *
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trans_create(int mode, int in_size, int out_size);
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void
trans_delete(struct trans *self);
void
trans_delete_from_child(struct trans *self);
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int
trans_get_wait_objs(struct trans *self, tbus *objs, int *count);
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int
trans_get_wait_objs_rw(struct trans *self,
tbus *robjs, int *rcount,
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tbus *wobjs, int *wcount, int *timeout);
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int
trans_check_wait_objs(struct trans *self);
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int
trans_force_read_s(struct trans *self, struct stream *in_s, int size);
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int
trans_force_write_s(struct trans *self, struct stream *out_s);
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int
trans_force_read(struct trans *self, int size);
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int
trans_force_write(struct trans *self);
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int
trans_write_copy(struct trans *self);
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int
trans_write_copy_s(struct trans *self, struct stream *out_s);
Rework transport connect logic There are a number of ways the existing transport connect logic in trans_connect could be improved for POSIX compatibility, and also slightly tidied up:- 1) The same socket is re-used for multiple connect attempts following failure which isn't behaviour defined by POSIX.1-2017 (although it works on Linux). 2) An asynchronous connect is started, and then after a short delay connect() is called again on the same socket. POSIX.1-2017 is clear that in this situation EALREADY is returned before the connection is established, but is silent on the behaviour expected when the connection is established. Returning success is an option, but so is returning EISCONN. The current code assumes the connect() call will succeed. 3) The code contains two virtually identical, quite complex loops for TCP and UNIX sockets, differing only in the calls to create a socket and connect it. 4) trans_connect() contains looping and retry logic, but this isn't seen as sufficient by the chansrv connect code in xrdp/xrdp_mm.c and the Xorg connect code in xup/xup.c. Both of these implement their own looping and retry logic on top of the logic in trans_connect(), resulting in slightly unpredictable behaviour with regard to timeouts. 5) A socket number can technically be zero, but in a couple of places this isn't allowed for. This PR attempts to correct the implementation of trans_connect(), and also to simplify the areas it is called from. As part of the PR, the signature of the server_is_term member of the xrdp module interface is changed to match the signature expected by the is_term member of a struct trans. This allows for trans_connect() in xrdp modules to directly access g_is_term() within the main xrdp executable. At the moment this functionality is only used by the xup module.
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/**
* Connect the transport to the specified destination
*
* @param self Transport
* @param server Destination server (TCP transports only)
* @param port TCP port, or UNIX socket to connect to
* @param timeout in milli-seconds for the operation
* @return 0 for success
*
* Multiple connection attempts may be made within the timeout period.
*
* If the operation is successful, 0 is returned and self->status will
* be TRANS_STATUS_UP
*/
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int
trans_connect(struct trans *self, const char *server, const char *port,
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int timeout);
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int
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trans_listen_address(struct trans *self, const char *port, const char *address);
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int
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trans_listen(struct trans *self, const char *port);
struct stream *
trans_get_in_s(struct trans *self);
struct stream *
trans_get_out_s(struct trans *self, int size);
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int
trans_set_tls_mode(struct trans *self, const char *key, const char *cert,
long ssl_protocols, const char *tls_ciphers);
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int
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trans_shutdown_tls_mode(struct trans *self);
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int
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trans_tcp_force_read_s(struct trans *self, struct stream *in_s, int size);
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#endif