Detect attempts to overflow input buffer
If application code hasn't properly sanitised the header_size
for a transport, it is possible for read requests to be issued
which overflow the input buffer. This change detects this
at a low level and bounces the read request.
The connected client is currently described in two places in
the xrdp_client_info structure:-
1) In the connection_description field. This was introduced as
field client_ip by commit d797b2cf49
for xrdp v0.6.0
2) In the client_addr and client_port fields introduced by commit
25369460a1 for xrdp v0.8.0
This commit unifies these two sets of fields into a single
set of fields describing the connection IP and port (for
AF_INET/AF_INET6 connections only) and a connection description
for all connection types.
The code in os_calls to provide client logging has been simplified
somewhat which should make it easier to add new connection types (e.g.
AF_VSOCK).
The old connection_description field used to be passed to sesman to
inform sesman of the IP address of the client, and also to provide
a string for 'C' field session policy matching. 'C' field session policy
matching does not actually need this string (see #2239), and so now only
the IP field is passed to sesman.
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.
If you run xrdp with a Unix Domain Socket (UDS) for the port specified in
/etc/xrdp/xrdp.ini then the first connection succeeds but subsequent
connections fail. In fact the UDS is deleted from the filesystem as soon
as the first connection is established.
Test case:
1. Edit /etc/xrdp/xrdp.ini to set "port=/var/run/xrdp-local.socket".
2. Restart xrdp.
3. Run the following. When rdesktop starts up and the logon dialog is
displayed, press "Cancel".
sudo socat TCP-LISTEN:12345 UNIX-CONNECT:/var/run/xrdp-local.socket &
rdesktop localhost:12345
4. Run the following:
sudo socat TCP-LISTEN:12346 UNIX-CONNECT:/var/run/xrdp-local.socket &
rdesktop localhost:12346
Expected behaviour: rdesktop starts up and displays the logon dialog.
Observed behaviour: rdesktop exits with "ERROR: Connection closed" and
socat exits with "No such file or directory.
This is because in the child process after forking, xrdp_listen_fork()
calls trans_delete() which deletes the UDS. Simply commenting out the
g_file_delete() and g_free() fixes this, but that isn't a proper solution
because trans_delete() is called from elsewhere where the UDS might no
longer be wanted.
Fix by adding a function trans_delete_from_child() that frees and clears
listen_filename before calling trans_delete(), and call the new function
from xrdp_listen_fork().
(Workaround: set "fork=false" in /etc/xrdp/xrdp.ini, because
trans_delete() is then not called.)
