Review Request 128761: Fix crash on exit

[Hugo Pereira Da Costa]

> On Aug. 27, 2016, 9:14 a.m., Hugo Pereira Da Costa wrote:
> > mmm. But then i think it is better (for commit history etc), to just revert the incriminated commit (and in oxygen as well), with a possible link to this RB. makes sense ?
> 
> Peter Wu wrote:
>     I tested the reverts for breeze and oxygen and that also works on Qt 5.7.0 (tested with `wireshark -o` (`exit()`s), `wireshark` + quit and the testcase).
>     
>     Reverted:
>     breeze 1430dd22ae74a09ba289dafe2be15628a0eddc15
>     oxygen e0376e1597f6e6b49e6343874e141b439565b749
>     
>     Due to `delete qApp->style()` however, it is in theory still possible to reach a use-after-free since QApplication owns it.
>     
>     I'll leave it up to you whether you take this patch or revert it, I'm fine with either.

i agree, obviously delete qApp->Style() must go too, and in fact that was the original patch introduced by D Faure, to oxygen (commit 2ffe20e1bfe93c921c5372b4d21447b1de308d4b), which i then copied to breeze with many other changes and wich was later on changed to the signal/slot delta function by D Edmundson.
So in the end, maybe it is indeed better to clean it all up in one go, possibly adding the relevant effectively reverted commits in the comments.


- Hugo


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On Aug. 27, 2016, 9:12 a.m., Peter Wu wrote:
> 
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> https://git.reviewboard.kde.org/r/128761/
> -----------------------------------------------------------
> 
> (Updated Aug. 27, 2016, 9:12 a.m.)
> 
> 
> Review request for Plasma, David Edmundson, David Faure, and Hugo Pereira Da Costa.
> 
> 
> Bugs: 356940
>     https://bugs.kde.org/show_bug.cgi?id=356940
> 
> 
> Repository: oxygen
> 
> 
> Description
> -------
> 
> Since Qt 5.6.0, Qt5 applications started crashing on exit. All signs
> point to this delete-on-destroy hack which was added to avoid outliving
> the plugin lifetime.
> 
> This method is wrong because the returned style is owned by the caller
> (QApplication, QProxyStyle, etc) and will cleaned up when those users
> are destructed.
> 
> Copied from breeze patch https://git.reviewboard.kde.org/r/128760/
> 
> 
> Diffs
> -----
> 
>   kstyle/oxygenstyleplugin.cpp 70b90d9 
> 
> Diff: https://git.reviewboard.kde.org/r/128761/diff/
> 
> 
> Testing
> -------
> 
> Started `QT_STYLE_OVERRIDE=oxygen LD_LIBRARY_PATH=... QT_PLUGIN_PATH=... wireshark -o` (an invalid option that triggers `exit(1)`) and observe a heap-use-after free similar to the one reported in the bug. Apply this patch, rebuild oxygen and notice that the crash is fixed. Also tested with "Testcase (ASAN)" from bug 356940, crash is also gone.
> 
> 
> Thanks,
> 
> Peter Wu
> 
>

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