[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Martin Gräßlin]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #11 from Martin Gräßlin  ---
No, I disagree on the ptrace change. It's important to get it set before any
interaction with the windowing system is done. And that happens in
QGuiApplication. Thus it needs to be before that.

The problem is also not the disable of ptrace, but the multi process
architecture in general. In the source tree there is another test top which can
simulate the architecture without having to rely on ksmserver. But requires to
build from source.

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #10 from Stefan Brüns  ---
Although I agree its not a bug in kscreenlocker, I still have two remarks:

1. kscreenlocker_greet is hard to debug, as it immediate turns of ptrac'ing,
and only allows it late during the initialization if '--testing' is set. Imho
it would be better to only disable ptrace right before app.exec().

I think from a security standpoint this would be fine as well, but allowed
catching errors during initilization.

Relevant greeter code:
https://github.com/KDE/kscreenlocker/blob/42ad07d79785e51641f97f7d20709fee6ab54060/greeter/main.cpp#L63

If you agree, I would prepare a patch.


2. stderr is not catched by the screen locker daemon. When starting
kscreenlocker_greet manually, e.g.:
$> XAUTHORITY=/home/stefan/.Xauthority_  /usr/lib64/libexec/kscreenlocker_greet
--testing
No protocol specified
QXcbConnection: Could not connect to display :0
Abgebrochen

, there is a somewhat helpful error message ("No protocol specified" points
clearly to xauth problems).

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Martin Gräßlin]

https://bugs.kde.org/show_bug.cgi?id=372197

Martin Gräßlin  changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution|--- |INVALID

--- Comment #9 from Martin Gräßlin  ---
Good investigation! But that also means it's not a bug in our software. We can
hardly protect against another process replacing the authority file ;-)

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #8 from Stefan Brüns  ---
Actually, both ~/.Xauthority and /tmp/xauth-$UID-_$DISPLAY are correct
locations, see https://cgit.kde.org/kinit.git/tree/src/kdeinit/kinit.cpp#n1470
for details.

The problem is caused by sddm.

When selecting "Switch User" and then starting a new session for an already
logged in user (which I triggered inadvertently from the lock screen, which
sometimes misbehaves on a dual screen setup - different bug), sddm replaces the
contents of the ~/Xauthority file.

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #7 from Stefan Brüns  ---
The processes which are not children of ksmserver are all programs which were
restored from a previous session.

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Martin Gräßlin]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #6 from Martin Gräßlin  ---
In the end all processes should be children of ksmserver. It's weird if you
have processes which are not.

But anyway: distro topic

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #5 from Stefan Brüns  ---
All processes with ~/.Xauthority are children of ksmserver, so this is
expected.

powerdevil, akonadi, firefox all have /tmp/xauth_1000-_0 in its env.

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Martin Gräßlin]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #4 from Martin Gräßlin  ---
Given the output it seems like konsole is the odd one. It's a dbus activated
application as far as I know.

Anyway I think you need to forward this report to your distribution. Somehow
the wrong xauthority ends up in your session. That is outside of kde's code

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #3 from Stefan Brüns  ---
for pid in 2388 2389 2393 2446 2428 2433 2439 ; do echo -n "$pid: " ; cat
/proc/$pid/cmdline | tr '\0' ' ' ; echo -ne "\n\t" ; cat /proc/$pid/environ |
tr '\0' '\n' | grep XAUTHORITY; echo ; done

2388: /usr/lib64/libexec/kf5/start_kdeinit --kded +kcminit_startup 
XAUTHORITY=/home/sbruens/.Xauthority

2389: kdeinit5: Running...   

2393: kded5 [kdeinit5]   

2446: /usr/bin/konsole -session
101bc13915311700014671252070035260022_1478617649_467193 
XAUTHORITY=/tmp/xauth-1000-_0

2428: /usr/bin/ksmserver 
XAUTHORITY=/home/sbruens/.Xauthority

2433: kwin_x11 -session
101bc13915311700014296180560019630002_1478617650_383503 
XAUTHORITY=/home/sbruens/.Xauthority

2439: plasmashell --shut-up 
XAUTHORITY=/home/sbruens/.Xauthority



pstree -A -p sbruens | grep  '+'
akonadi_control(2602)-+-akonadi_akonote(2940)-+-{QDBusConnection}(2944)
  |-akonadi_archive(2941)-+-{QDBusConnection}(2951)
  ...
  |-akonadi_notes_a(3072)-+-{QDBusConnection}(3097)
  |-akonadi_sendlat(3078)-+-{QDBusConnection}(3116)
  |-akonadiserver(2612)-+-mysqld(2636)-+-{mysqld}(2664)
at-spi-bus-laun(2867)-+-{dconf worker}(2869)
dconf-service(2425)-+-{gdbus}(2430)
gnome-keyring-d(2688)-+-{gdbus}(2698)
gvfsd(2884)-+-{gdbus}(2886)
gvfsd-fuse(2889)-+-{gdbus}(2903)
kaccess(2401)-+-{QDBusConnection}(2402)
kactivitymanage(2481)-+-{QDBusConnection}(2483)
kdeinit5(2389)-+-firefox(2512)-+-Web Content(3000)-+-{Chrome_ChildThr}(3008)
   |-kded5(2393)-+-{QDBusConnection}(2398)
   |-klauncher(2390)-+-{QDBusConnection}(2392)
   |-konsole(2446)-+-bash(2661)
   |   |-bash(2741)-+-grep(4753)
   |-korgac(2464)-+-{QDBusConnection}(2517)
   |-ksmserver(2428)-+-baloo_file(2436)---{QDBusConnection}(2452)
   | |-krunner(2437)-+-{QDBusConnection}(2458)
   | |-kwin_x11(2433)-+-{QDBusConnection}(2434)
   | |-plasmashell(2439)-+-{QDBusConnection}(2453)
   |
|-polkit-kde-auth(2440)-+-{QDBusConnection}(2445)
   |
|-xembedsniproxy(2441)-+-{QDBusConnection}(2451)
   `-org_kde_powerde(2456)-+-{QDBusConnection}(2461)
kglobalaccel5(2412)-+-{QDBusConnection}(2415)
kscreen_backend(2417)-+-{QDBusConnection}(2427)
kwalletd5(2610)-+-{QDBusConnection}(2633)
pulseaudio(2503)-+-{alsa-sink-ALC66}(2564)
startkde(2266)-+-gpg-agent(2352)

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[kscreenlocker] [Bug 372197] wrong XAUTHORITY setting leads to crashing kscreenlocker_greeter

[Stefan Brüns]

https://bugs.kde.org/show_bug.cgi?id=372197

--- Comment #2 from Stefan Brüns  ---
Side note: this seems to also affect the "Logout", "Reboot" Actions from
KDE->Leave menu

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