Bug#939400: sddm: Auth: sddm-helper exited with 11

[Konomi <konomikitten@gmail.com>]

Package: sddm
Version: 0.18.0-1
Severity: grave
Tags: upstream
Justification: renders package unusable

Quoting the upstream bug report:

"sddm-greeter needs execution rights at /var/lib/sddm/.cache/sddm-greeter/qmlcache/*.qmlc. 
krunner needs execution at /home/user/.cache/krunner/qmlcache/*.qmlc. It breaks 
when /var and /home partitions are mounted with noexec flag which is often used on 
hardened setups or Trusted Path Execution available on hardened linux kernels.

As for now it could be fixed by disabling qml cache by setting QML_DISABLE_DISK_CACHE=1
environment variable. Is there a chance that qt will check permission rights first then
quietly disable qmlcache per app instead of crashing?

Alternatively it could create cachedir somewhere in /usr/lib/qt same as python3 have
it's pycache dir."

Upstream bug report: https://bugreports.qt.io/browse/QTBUG-58508

The work around of adding QML_DISABLE_DISK_CACHE=1 to /etc/enviroment got sddm working
for me again. Without the work around sddm will start but show just a black screen, so
I've marked this bug as grave since it completely breaks the package.


-- System Information:
Debian Release: bullseye/sid
  APT prefers testing
  APT policy: (500, 'testing'), (120, 'stable'), (110, 'unstable'), (100, 'experimental')
Architecture: amd64 (x86_64)

Kernel: Linux 5.2.0-2-amd64 (SMP w/1 CPU core)
Kernel taint flags: TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=en_AU.UTF-8, LC_CTYPE=en_AU.UTF-8 (charmap=UTF-8), LANGUAGE=en_AU:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages sddm depends on:
ii  adduser                 3.118
ii  debconf [debconf-2.0]   1.5.73
ii  libc6                   2.28-10
ii  libgcc1                 1:9.2.1-4
ii  libpam0g                1.3.1-5
ii  libqt5core5a            5.11.3+dfsg1-4
ii  libqt5dbus5             5.11.3+dfsg1-4
ii  libqt5gui5              5.11.3+dfsg1-4
ii  libqt5network5          5.11.3+dfsg1-4
ii  libqt5qml5              5.11.3-4
ii  libqt5quick5            5.11.3-4
ii  libstdc++6              9.2.1-4
ii  libsystemd0             242-5
ii  libxcb-xkb1             1.13.1-2
ii  libxcb1                 1.13.1-2
ii  qml-module-qtquick2     5.11.3-4
ii  x11-common              1:7.7+19
ii  xserver-xorg [xserver]  1:7.7+19

Versions of packages sddm recommends:
ii  haveged                                1.9.4-2
ii  libpam-systemd                         242-5
ii  sddm-theme-debian-elarun [sddm-theme]  0.18.0-1
ii  sddm-theme-maui [sddm-theme]           0.18.0-1

Versions of packages sddm suggests:
pn  libpam-kwallet5           <none>
pn  qtvirtualkeyboard-plugin  <none>

-- debconf information:
  sddm/daemon_name: /usr/bin/sddm
* shared/default-x-display-manager: sddm