![]() ![]() > xscreensaver, where the button is totally hacked up, > The currently logged in user could choose to run her own version of DDEFAULT_PATH_PREFIX=/usr/X11R6/lib/xscreensaver) E.g., they could just asĮasily replace "qix" as "gdmflexiserver". Xscreensaver sees, the game is already lost. Xscreensaver's primary function is to execute programs, so I think weĬan assume that if an attacker can manipulate the $PATH that To "walk through all the F-keys until you find the blue login screen". For instance, I would have to teach my mom Users, who are unaware of the hidden powers ofĬtrl+Alt+F(|1). Of course, this would not be very convenient for non-computer-literate This is something an extremely paranoid user could do to be absolutelyĪssured that she is logging into a genuine gdm. ![]() The fake one could be killed with aĬtrl+Alt+Backspace and, unlike the genuine one, it wouldn't come back. Genuine one, however, there would always be at least one genuine gdm Present, and a person walking up to the computer need only browseĮven so, a gdm login screen could be faked on a vt other than the In such a case, the genuine gdm login screen would always be User, and to switch vts to the new X server which houses the user's "fork off" the session to a new X server after authenticating the Perhaps the most secure way to allow multiple logins is for gdm to The above question can be asked in any "Switch User" scenario. I suppose, looking at the way OSX does it, I'm lead to conclude that Login" button, she will get a brand-spanking new, completely genuine Wanting to log in be absolutely assured that when she presses the "New OnceĪgain, the fake login scenario comes to mind.īottom line: How can a user who walks up to the screenlocked computer What she wants, irrespective of what we tried to make it do. Xscreensaver, where the button is totally hacked up, so it will do The currently logged in user could choose to run her own version of That cannot be overridden by the currently logged-in user ? Is there someplace we can specify the path to gdmflexiserver in a way My view of the consequences is reduced to the scenario speculated X resources can be overwritten by the logged in user, correct ? If so, Xinit $/my_fake_gdm_login_screen_I_wrote_in_GTK - :1 User could /fake/ a login screen and harvest a password like so: The currently logged in user may prefix the PATH with her ownĭirectories and we may end up executing some other binary. Pfile = popen ("which gdmflexiserver", "r") Gdmflexiserver binary securely so that, when we finally execute it, weĬan be relatively sure that we're executing the gdmflexiserver binaryĪnd not another binary named gdmflexiserver. We will need to think of a way to determine the path to the However, I share Jamie's jitters over executing stuff from the login Re-implementing part of the protocol from the gdmflexiserver sources, I would be the first to change my patch over to fork/execvp instead of Good luck to anyone else trying to log in via gdm.Īctual Results: It's very difficult to start another graphical login manager, let alone another GNOME session.Įxpected Results: There should be a way to start a new login screen - much like fast user switching on Windoze or OSX. Version-Release number of selected component (if applicable):ģ. The patch has one shortcoming: The mouse is either invisible or entirely disabled during the lifetime of the xscreensaver password dialog, so, while the button works when running the password dialog from a test utility (part of xscreensaver), it doesn't work "live", because there's no mouse available for clicking on it. This would allow computers used by more than one person to easily provide multiple graphical logins on demand. I have written a patch against xscreensaver-4.19 as available on Jamie Zawinski's Web site which adds a "New Login" button to the xscreensaver password dialog which, when pressed, initiates a dialog with gdm over /tmp/.gdm_socket and asks it to start a new flexi server. ![]()
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