Unity8 (QtMir) crashed (on login or display change) in TiledDisplayConfigurationPolicy::apply_to() [tileddisplayconfigurationpolicy.cpp:41]

[errors.ubuntu.com bug bridge]

The Ubuntu Error Tracker has been receiving reports about a problem regarding unity8. This problem was most recently seen with version 8.11+16.04.20160310.4-0ubuntu1, the problem page at https://errors.ubuntu.com/problem/ad2b8406e4a16551fc78ba9793cc41fe4d801653 contains more details.

[Daniel van Vugt (vanvugt)]

It's a simple array overrun in QtMir:

                nextTopLeftPosition += output.modes[output.preferred_mode_index].size.width.as_int();

Looks like it's missing a check for the possibility of there being no preferred mode:

    output.preferred_mode_index >= modes.size()

Which is possible, and almost common (particularly on TVs).

[Daniel van Vugt (vanvugt)]

We also encountered this issue back in 2014:

https://code.launchpad.net/~vanvugt/mir/fix-1395405/+merge/242583

[Launchpad Janitor (janitor)]

This bug was fixed in the package qtmir - 0.4.8+16.04.20160329.1-0ubuntu1

---------------
qtmir (0.4.8+16.04.20160329.1-0ubuntu1) xenial; urgency=medium

  [ Daniel van Vugt ]
  * Don't use preferred_mode_index. Some devices like TVs don't provide
    a preferred mode, so preferred_mode_index may be out of range (a
    clumsy way to represent 'none'). Instead use the resolution of the
    current display mode, which should always be in range. (LP:
    #1560497)

 -- Michał Sawicz <email address hidden> Tue, 29 Mar 2016 19:24:13 +0000