Add optional UID to DISPLAY() in chansrvport

The code to determine the socket address of chansrv when using
a manually started xrdp-chansrv may need some help determining
the UID of the session.

This commit allows a UID to be optionally specified in the
DISPLAY() function, if the code is unable to determine the
UID automatically from the connection parameters.

If a manual chansrvport is entered, xrdp now logs what it is
connecting to, to assist in debugging.

(cherry picked from commit d17d12d)

docs/man/xrdp.ini.5.in

@@ -358,14 +358,17 @@ Specifies the session type. The default, \fI0\fR, is Xvnc,
 and \fI20\fR is Xorg with xorgxrdp modules.
 
 .TP
-\fBchansrvport\fR=\fBDISPLAY(\fR\fIn\fR\fB)\fR|\fI/path/to/domain-socket\fR
+\fBchansrvport\fR=\fBDISPLAY(\fR\fIn\fR\fB)\fR|\fBDISPLAY(\fR\fIn,u\fR\fB)\fR||\fI/path/to/domain-socket\fR
 Asks xrdp to connect to a manually started \fBxrdp-chansrv\fR instance.
 This can be useful if you wish to use to use xrdp to connect to a VNC session
 which has been started other than by \fBxrdp-sesman\fR, as you can then make
 use of \fBxrdp\-chansrv\fR facilities in the VNC session.
 
-The first form of this setting is recommended, replacing \fIn\fR with the
-X11 display number of the session.
+Either the first or second form of this setting is recommended. Replace
+\fIn\fR with the X11 display number of the session, and (if applicable)
+\fIu\fR with the numeric ID of the session. The second form is only
+required if \fBxrdp\fR is unable to determine the session uid from the
+other values in the connection block.
 
 .SH "EXAMPLES"
 This is an example \fBxrdp.ini\fR:

xrdp/xrdp.ini.in

@@ -255,10 +255,6 @@ port=-1
 ; Disable requested encodings to support buggy VNC servers
 ; (1 = ExtendedDesktopSize)
 #disabled_encodings_mask=0
-; Use this to connect to a chansrv instance created outside of sesman
-; (e.g. as part of an x11vnc console session). Replace '0' with the
-; display number of the session
-#chansrvport=DISPLAY(0)
 
 ; Generic VNC Proxy
 ; Tailor this to specific hosts and VNC instances by specifying an ip
@@ -273,6 +269,15 @@ password=ask
 #pamusername=asksame
 #pampassword=asksame
 #delay_ms=2000
+; Use one of these to connect to a chansrv instance created outside of sesman
+; (e.g. as part of an x11vnc console session). Replace 'n' with the
+; display number of the session, and (if applicable) 'u' with the numeric
+; UID of the session.
+;
+; If 'username' or 'pamusername' is set, you probably don't need to use
+; the two parameter variant with 'u'.
+#chansrvport=DISPLAY(n)
+#chansrvport=DISPLAY(n,u)
 
 ; Generic RDP proxy using NeutrinoRDP
 ; Tailor this to specific hosts by specifying an ip and port and setting

xrdp/xrdp_mm.c

@@ -2859,28 +2859,60 @@ static int
 parse_chansrvport(const char *value, char *dest, int dest_size, int uid)
 {
     int rv = 0;
+    int dnum = 0;
 
     if (g_strncmp(value, "DISPLAY(", 8) == 0)
     {
         const char *p = value + 8;
         const char *end = p;
 
-        /* Check next chars are digits followed by ')' */
+        /* Check next chars are digits */
         while (isdigit(*end))
         {
             ++end;
         }
 
-        if (end == p || *end != ')')
+        if (end == p)
         {
-            LOG(LOG_LEVEL_WARNING, "Ignoring invalid chansrvport string '%s'",
+            LOG(LOG_LEVEL_WARNING,
+                "Ignoring chansrvport string with bad display number '%s'",
                 value);
-            rv = -1;
+            return -1;
         }
-        else
+
+        dnum = g_atoi(p);
+
+        if (*end == ',')
         {
-            g_snprintf(dest, dest_size, XRDP_CHANSRV_STR, uid, g_atoi(p));
+            /* User has specified a UID override
+             * Check next chars are digits */
+            p = end + 1;
+            end = p;
+
+            while (isdigit(*end))
+            {
+                ++end;
+            }
+
+            if (end == p)
+            {
+                LOG(LOG_LEVEL_WARNING,
+                    "Ignoring chansrvport string with bad uid '%s'",
+                    value);
+                return -1;
+            }
+            uid = g_atoi(p);
         }
+
+        if (*end != ')')
+        {
+            LOG(LOG_LEVEL_WARNING,
+                "Ignoring badly-terminated chansrvport string '%s'",
+                value);
+            return -1;
+        }
+
+        g_snprintf(dest, dest_size, XRDP_CHANSRV_STR, uid, dnum);
     }
     else
     {
@@ -3152,13 +3184,14 @@ xrdp_mm_connect_sm(struct xrdp_mm *self)
             case MMCS_SESSION_LOGIN:
             {
                 // Finished with the gateway login
+                // Leave the UID set in case we need it for the chansrvport
+                // string
                 if (self->use_gw_login)
                 {
                     xrdp_wm_log_msg(self->wm, LOG_LEVEL_INFO,
                                     "access control check was successful");
                     // No reply needed for this one
                     status = scp_send_logout_request(self->sesman_trans);
-                    self->uid = -1;
                 }
 
                 if (status == 0 && self->use_sesman)
@@ -3232,12 +3265,12 @@ xrdp_mm_connect_sm(struct xrdp_mm *self)
                 {
                     char portbuff[XRDP_SOCKETS_MAXPATH];
 
-                    xrdp_wm_log_msg(self->wm, LOG_LEVEL_INFO,
-                                    "Connecting to chansrv");
                     if (self->use_sesman)
                     {
                         g_snprintf(portbuff, sizeof(portbuff),
                                    XRDP_CHANSRV_STR, self->uid, self->display);
+                        xrdp_wm_log_msg(self->wm, LOG_LEVEL_INFO,
+                                        "Connecting to chansrv");
                     }
                     else
                     {
@@ -3246,6 +3279,9 @@ xrdp_mm_connect_sm(struct xrdp_mm *self)
                         parse_chansrvport(cp, portbuff, sizeof(portbuff),
                                           self->uid);
 
+                        xrdp_wm_log_msg(self->wm, LOG_LEVEL_INFO,
+                                        "Connecting to chansrv on %s",
+                                        portbuff);
                     }
                     xrdp_mm_update_allowed_channels(self);
                     xrdp_mm_chansrv_connect(self, portbuff);