GNOME Bugzilla – Bug 354746
gdm does not handle xdmcp and tcp deny connections to X server correctly
Last modified: 2007-08-16 02:17:05 UTC
Please describe the problem: Open gdmsetup, then click tab Security, then : - select box "Enable xdmcp" - then if you hit box "Deny TCP connections to X server (disables xforwarding, but does not affect xdmcp)", you cannot get a display from another machine, so that affects xdmcp. When you deselect the box, that works. Steps to reproduce: 1. Open gdmsetup 2. Click tab Security 3. Select box "Enable xdmcp" 4. Select box "Deny TCP connections to X server (disables xforwarding, but does not affect xdmcp)" 5. Connect to another machine and try to send the display on the first one Actual results: The display does not come on the first machine, you have an error "Cannot open <machine>:0" Expected results: The display should be opened on the first machine (that works when you deselect the box "Deny TCP..." and restart gdm). Does this happen every time? Yes Other information:
You can look at the code in daemon/server.c and see that the only thing that setting DisallowTCP does is add "-nolisten" to the call to start the Xserver. Perhaps in some environments this does affect XDMCP and the docs and comment in gdmsetup should be updated. I thought setting -nolisten didn't affect TCP, but perhaps it does. Could someone verify? This is probably a documentation bug.
I have been suggesting this workaround to people on the gdm-list for some time, and people seem to report that it doesn't have any effect on breaking XDMCP. So I think this bug has likely been fixed. If people see problems in this area, please file a new bug or reopen this one with more information.