197 lines
5.2 KiB
Plaintext
197 lines
5.2 KiB
Plaintext
This document describes the multiplexing protocol used by ssh(1)'s
|
|
ControlMaster connection-sharing.
|
|
|
|
Most messages from the client to the server contain a "request id" field.
|
|
This field is returned in replies as "client request id" to facilitate
|
|
matching of responses to requests.
|
|
|
|
1. Connection setup
|
|
|
|
When a multiplexing connection is made to a ssh(1) operating as a
|
|
ControlMaster from a ssh(1) in multiplex slave mode, the first
|
|
action of each is to exchange hello messages:
|
|
|
|
uint32 MUX_MSG_HELLO
|
|
uint32 protocol version
|
|
string extension name [optional]
|
|
string extension value [optional]
|
|
...
|
|
|
|
The current version of the mux protocol is 4. A slave should refuse
|
|
to connect to a master that speaks an unsupported protocol version.
|
|
Following the version identifier are zero or more extensions
|
|
represented as a name/value pair. No extensions are currently
|
|
defined.
|
|
|
|
2. Opening sessions
|
|
|
|
To open a new multiplexed session, a client may send the following
|
|
request:
|
|
|
|
uint32 MUX_C_MSG_NEW_SESSION
|
|
uint32 request id
|
|
string reserved
|
|
bool want tty flag
|
|
bool want X11 forwarding flag
|
|
bool want agent flag
|
|
bool subsystem flag
|
|
uint32 escape char
|
|
string terminal type
|
|
string command
|
|
string environment string 0 [optional]
|
|
...
|
|
|
|
To disable the use of an escape character, "escape char" may be set
|
|
to 0xffffffff. "terminal type" is generally set to the value of
|
|
$TERM. zero or more environment strings may follow the command.
|
|
|
|
The client then sends its standard input, output and error file
|
|
descriptors (in that order) using Unix domain socket control messages.
|
|
|
|
The contents of "reserved" are currently ignored.
|
|
|
|
If successful, the server will reply with MUX_S_SESSION_OPENED
|
|
|
|
uint32 MUX_S_SESSION_OPENED
|
|
uint32 client request id
|
|
uint32 session id
|
|
|
|
Otherwise it will reply with an error: MUX_S_PERMISSION_DENIED or
|
|
MUX_S_FAILURE.
|
|
|
|
Once the server has received the fds, it will respond with MUX_S_OK
|
|
indicating that the session is up. The client now waits for the
|
|
session to end. When it does, the server will send an exit status
|
|
message:
|
|
|
|
uint32 MUX_S_EXIT_MESSAGE
|
|
uint32 session id
|
|
uint32 exit value
|
|
|
|
The client should exit with this value to mimic the behaviour of a
|
|
non-multiplexed ssh(1) connection. Two additional cases that the
|
|
client must cope with are it receiving a signal itself and the
|
|
server disconnecting without sending an exit message.
|
|
|
|
3. Health checks
|
|
|
|
The client may request a health check/PID report from a server:
|
|
|
|
uint32 MUX_C_ALIVE_CHECK
|
|
uint32 request id
|
|
|
|
The server replies with:
|
|
|
|
uint32 MUX_S_ALIVE
|
|
uint32 client request id
|
|
uint32 server pid
|
|
|
|
4. Remotely terminating a master
|
|
|
|
A client may request that a master terminate immediately:
|
|
|
|
uint32 MUX_C_TERMINATE
|
|
uint32 request id
|
|
|
|
The server will reply with one of MUX_S_OK or MUX_S_PERMISSION_DENIED.
|
|
|
|
5. Requesting establishment of port forwards
|
|
|
|
A client may request the master to establish a port forward:
|
|
|
|
uint32 MUX_C_OPEN_FORWARD
|
|
uint32 request id
|
|
uint32 forwarding type
|
|
string listen host
|
|
string listen port
|
|
string connect host
|
|
string connect port
|
|
|
|
forwarding type may be MUX_FWD_LOCAL, MUX_FWD_REMOTE, MUX_FWD_DYNAMIC.
|
|
|
|
A server may reply with a MUX_S_OK, a MUX_S_PERMISSION_DENIED or a
|
|
MUX_S_FAILURE.
|
|
|
|
5. Requesting closure of port forwards
|
|
|
|
A client may request the master to establish a port forward:
|
|
|
|
uint32 MUX_C_OPEN_FORWARD
|
|
uint32 request id
|
|
uint32 forwarding type
|
|
string listen host
|
|
string listen port
|
|
string connect host
|
|
string connect port
|
|
|
|
forwarding type may be MUX_FWD_LOCAL, MUX_FWD_REMOTE, MUX_FWD_DYNAMIC.
|
|
|
|
A server may reply with a MUX_S_OK, a MUX_S_PERMISSION_DENIED or a
|
|
MUX_S_FAILURE.
|
|
|
|
6. Requesting stdio forwarding
|
|
|
|
A client may request the master to establish a stdio forwarding:
|
|
|
|
uint32 MUX_C_NEW_STDIO_FWD
|
|
uint32 request id
|
|
string reserved
|
|
string connect host
|
|
string connect port
|
|
|
|
The client then sends its standard input and output file descriptors
|
|
(in that order) using Unix domain socket control messages.
|
|
|
|
The contents of "reserved" are currently ignored.
|
|
|
|
A server may reply with a MUX_S_SESSION_OPEED, a MUX_S_PERMISSION_DENIED
|
|
or a MUX_S_FAILURE.
|
|
|
|
7. Status messages
|
|
|
|
The MUX_S_OK message is empty:
|
|
|
|
uint32 MUX_S_OK
|
|
uint32 client request id
|
|
|
|
The MUX_S_PERMISSION_DENIED and MUX_S_FAILURE include a reason:
|
|
|
|
uint32 MUX_S_PERMISSION_DENIED
|
|
uint32 client request id
|
|
string reason
|
|
|
|
uint32 MUX_S_FAILURE
|
|
uint32 client request id
|
|
string reason
|
|
|
|
7. Protocol numbers
|
|
|
|
#define MUX_MSG_HELLO 0x00000001
|
|
#define MUX_C_NEW_SESSION 0x10000002
|
|
#define MUX_C_ALIVE_CHECK 0x10000004
|
|
#define MUX_C_TERMINATE 0x10000005
|
|
#define MUX_C_OPEN_FORWARD 0x10000006
|
|
#define MUX_C_CLOSE_FORWARD 0x10000007
|
|
#define MUX_S_OK 0x80000001
|
|
#define MUX_S_PERMISSION_DENIED 0x80000002
|
|
#define MUX_S_FAILURE 0x80000003
|
|
#define MUX_S_EXIT_MESSAGE 0x80000004
|
|
#define MUX_S_ALIVE 0x80000005
|
|
#define MUX_S_SESSION_OPENED 0x80000006
|
|
|
|
#define MUX_FWD_LOCAL 1
|
|
#define MUX_FWD_REMOTE 2
|
|
#define MUX_FWD_DYNAMIC 3
|
|
|
|
XXX TODO
|
|
XXX extended status (e.g. report open channels / forwards)
|
|
XXX graceful close (delete listening socket, but keep existing sessions active)
|
|
XXX lock (maybe)
|
|
XXX watch in/out traffic (pre/post crypto)
|
|
XXX inject packet (what about replies)
|
|
XXX server->client error/warning notifications
|
|
XXX port0 rfwd (need custom response message)
|
|
XXX send signals via mux
|
|
|
|
$OpenBSD: PROTOCOL.mux,v 1.1 2010/01/26 01:28:35 djm Exp $
|