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krotuss
Apprentice
Apprentice


Joined: 01 Aug 2008
Posts: 157

PostPosted: Sat May 28, 2016 4:25 pm    Post subject: SDDM DoS Reply with quote

Hi, I just found out that executing
Code:

/usr/bin/sddm

as unprivileged user from running KDE session results in garbled graphics (horizontal lines). Although machine is still responsive (caps/num lock lights) and is possible to soft-reboot using ctrl+alt+del enter sequence, I was unable to ctrl+alt+fx to other virtual terminals. My graphics driver is radeon. Can anybody confirm if this occurs with other setups as well? Does anybody know how to recover from this? Is it safe to remove execute rights for others? Thanks.

EDIT:
/usr/bin/sddm is not SUID binary so removing exec rights is not a way to secure system...
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eccerr0r
Watchman
Watchman


Joined: 01 Jul 2004
Posts: 7196
Location: almost Mile High in the USA

PostPosted: Sat May 28, 2016 5:42 pm    Post subject: Reply with quote

Sounds like a bug. FGLRX or OSS?
Might be able to do the same by running /usr/bin/X ?
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Intel Core i7 2700K@ 4.1GHz/HD3000 graphics/8GB DDR3/180GB SSD
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Athenian200
n00b
n00b


Joined: 27 Nov 2005
Posts: 18
Location: Dallas, TX USA

PostPosted: Sun May 29, 2016 12:15 pm    Post subject: Reply with quote

I've had similar issues in the past.

Can you try using SSH to login remotely and kill the X session from the remote terminal? A lot of times even when X is locked up so badly that it won't respond to anything, you can get into the computer via SSH and kill X to get your main console back. Or at least view logs and reboot the system if X won't return control to Bash even after being killed.

Note that in order to do this, you need to install SSH on your machine, and add a normal user account to the "wheel" group. You'll then have to login as that normal user and type "su" in order to become root. It's a pain in the butt that you can't just login as root over SSH, but I assume it's done that way for security reasons.

I have no idea how to solve your problem, but that's my suggestion for recovering from it while you test.
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krotuss
Apprentice
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Joined: 01 Aug 2008
Posts: 157

PostPosted: Mon May 30, 2016 6:43 pm    Post subject: Reply with quote

@eccerr0r: its OSS x11-drivers/xf86-video-ati-7.7.0, X detects that ist already running so it doesn't result in same issue
Code:

_XSERVTransSocketUNIXCreateListener: ...SocketCreateListener() failed
_XSERVTransMakeAllCOTSServerListeners: server already running
(EE)
Fatal server error:
(EE) Cannot establish any listening sockets - Make sure an X server isn't already running(EE)
(EE)
Please consult the The X.Org Foundation support
         at http://wiki.x.org
 for help.
(EE) Please also check the log file at "/var/log/Xorg.0.log" for additional information.
(EE)
(EE) Server terminated with error (1). Closing log file.


@Athenian200: I have no other use for ssh access on my computer so I am reluctant to increase attack surface just to be able to recover from this. I have also some doubts if just killing X would restore graphics. Perhaps vbetool could help, maybe I will try over weekend. Thanks.
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eccerr0r
Watchman
Watchman


Joined: 01 Jul 2004
Posts: 7196
Location: almost Mile High in the USA

PostPosted: Tue May 31, 2016 4:45 am    Post subject: Reply with quote

Try X :1
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