Bug#1016050: sddm: intermittedly shows black page instead of login screen

[Paolo Greppi]

Package: sddm
X-Debbugs-Cc: paolo.gre...@libpf.com
Version: 0.19.0-3
Severity: important










  lug 25 17:25:50 localhost.localdomain sddm-helper[1573]: [PAM] Ended.

    lug 25 17:25:50 localhost.localdomain sddm[1442]: Greeter stopped.



In success.log after "Greeter session started successfully" it goes on with:


  lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: [PAM] returning.

  lug 26 06:54:38 localhost.localdomain sddm[1503]: Greeter stopped.

  lug 26 06:54:38 localhost.localdomain sddm[1503]: Session started



It looks to me as a race condition.

Probably the PAM system is not yet ready when sddm-helper tries to connect.

Paolo


-- System Information:
Debian Release: 11.4
  APT prefers stable-updates

Architecture: amd64 (x86_64)

Kernel: Linux 5.10.0-16-amd64 (SMP w/12 CPU threads)

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]   1.5.77
ii  libc6                   2.31-13+deb11u3
ii  libgcc-s1               10.2.1-6
ii  libpam0g                1.4.0-9+deb11u1
ii  libqt5core5a            5.15.2+dfsg-9
ii  libqt5dbus5             5.15.2+dfsg-9
ii  libqt5gui5              5.15.2+dfsg-9
ii  libqt5network5          5.15.2+dfsg-9
ii  libqt5qml5              5.15.2+dfsg-6
ii  libqt5quick5            5.15.2+dfsg-6
ii  libstdc++6              10.2.1-6
ii  libsystemd0             247.3-7
ii  libxcb-xkb1             1.14-3
ii  libxcb1                 1.14-3
ii  qml-module-qtquick2     5.15.2+dfsg-6
ii  x11-common              1:7.7+22
ii  xauth                   1:1.1-1
ii  xserver-xorg [xserver]  1:7.7+22

Versions of packages sddm recommends:
ii  haveged                                1.9.14-1
ii  libpam-systemd                         247.3-7
ii  sddm-theme-breeze [sddm-theme]         4:5.20.5-6
ii  sddm-theme-debian-breeze [sddm-theme]  4:5.20.5-6
ii  sddm-theme-debian-elarun [sddm-theme]  0.19.0-3
ii  sddm-theme-debian-maui [sddm-theme]    0.19.0-3
ii  sddm-theme-maldives [sddm-theme]       0.19.0-3
ii  sddm-theme-maui [sddm-theme]           0.19.0-3

Versions of packages sddm suggests:
ii  libpam-kwallet5           5.20.5-1
pn  qtvirtualkeyboard-plugin  <none>

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

About 90% of the times after a fresh reboot, sddm shows a black page with mouse pointer instead of the login screen. The systemd sddm service is up and running. If I restart it on tty 1, the login screen reappears. I attach two extracts from journalctl -u sddm, one for a successful boot, where the login screen was showed so that I could login (success.log) and one for a non-successful boot (failure.log). They are similar up to "Greeter session started successfully". But in failure.log after that it says: lug 25 17:25:50 localhost sddm[1442]: Greeter session started successfully lug 25 17:25:50 localhost.localdomain sddm-helper[1573]: [PAM] Closing session lug 25 17:25:50 localhost.localdomain sddm-helper[1573]: pam_unix(sddm-greeter:session): session closed for user sddm lug 25 17:25:50 localhost.localdomain sddm[1442]: Auth: sddm-helper exited with 6 In that case at 17:27:21 I restarted the service ("Signal received: SIGTERM") and then I could login. lug 26 06:54:27 localhost sddm[1503]: Greeter session started successfully lug 26 06:54:27 localhost sddm[1503]: Message received from greeter: Connect lug 26 06:54:38 localhost.localdomain sddm[1503]: Message received from greeter: Login lug 26 06:54:38 localhost.localdomain sddm[1503]: Reading from "/usr/share/xsessions/plasma.desktop" lug 26 06:54:38 localhost.localdomain sddm[1503]: Reading from "/usr/share/xsessions/plasma.desktop" lug 26 06:54:38 localhost.localdomain sddm[1503]: Session "/usr/share/xsessions/plasma.desktop" selected, command: "/usr/bin/startplasma-x11" lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: [PAM] Starting... lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: [PAM] Authenticating... lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: [PAM] Preparing to converse... lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: [PAM] Conversation with 1 messages lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: pam_kwallet5(sddm:auth): (null): pam_sm_authenticate lug 26 06:54:38 localhost.localdomain sddm[1503]: Authenticated successfully lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: pam_kwallet5(sddm:setcred): pam_kwallet5: pam_sm_setcred lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: pam_unix(sddm:session): session opened for user paolog(uid=1000) by (uid=0) lug 26 06:54:38 localhost.localdomain sddm[1503]: Auth: sddm-helper exited successfully lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: pam_kwallet5(sddm:session): pam_kwallet5: pam_sm_open_session lug 26 06:54:38 localhost.localdomain sddm-helper[1970]: Starting: "/etc/sddm/Xsession \"/usr/bin/startplasma-x11\"" So the difference is that in the second case sddm gets to "Message received from greeter: Connect" and all goes well, whereas in the first case that status is never reached because sddm-helper closes the PAM session and bails out, causing the greeter to stop. APT policy: (500, 'stable-updates'), (500, 'stable-security'), (500, 'stable-debug'), (500, 'stable'), (400, 'unstable') Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE Locale: LANG=it_IT.UTF-8, LC_CTYPE=it_IT.UTF-8 (charmap=UTF-8), LANGUAGE not set

failure.log.xz
Description: application/xz

success.log.xz
Description: application/xz