1978136 - Null crash in [@ gtk_style_context_get_path] via GtkWidgets::CreateSubStyleWithClass

Status: RESOLVED FIXED

(Core :: Widget: Gtk, defect)

Description

[Andrew McCreight [:mccr8]]

Crash report: https://crash-stats.mozilla.org/report/index/ca9d82c2-63fb-4656-af1f-716860250716

Reason:

SIGSEGV / SEGV_MAPERR

Top 10 frames:

0  libgtk-3.so.0  gtk_style_context_get_path  /tmp/buildd/gtk+3.0-3.14.5/gtk/gtkstylecontext.c:1432
1  libxul.so  mozilla::widget::GtkWidgets::CreateSubStyleWithClass(mozilla::widget::GtkWidg...  widget/gtk/GtkWidgets.cpp:398
2  libxul.so  mozilla::widget::GtkWidgets::GetWidgetStyleInternal(mozilla::widget::GtkWidge...  widget/gtk/GtkWidgets.cpp
2  libxul.so  mozilla::widget::GtkWidgets::GetStyle(mozilla::widget::GtkWidgets::Type, int,...  widget/gtk/GtkWidgets.cpp:528
3  libxul.so  nsLookAndFeel::PerThemeData::Init()  widget/gtk/nsLookAndFeel.cpp:2216
4  libxul.so  nsLookAndFeel::Initialize()  widget/gtk/nsLookAndFeel.cpp:1745
5  libxul.so  nsXPLookAndFeel::GetInstance()  widget/nsXPLookAndFeel.cpp:373
6  libxul.so  mozilla::LookAndFeel::EnsureInit()  widget/nsXPLookAndFeel.cpp:1491
6  libxul.so  nsContentUtils::Init()  dom/base/nsContentUtils.cpp:1138
6  libxul.so  nsLayoutStatics::Initialize()  layout/build/nsLayoutStatics.cpp:156

The volume is low. There have been 28 crashes in the last 3 months, all on 142a1, so maybe it is a regression? These are null crashes. Maybe GtkWidgets::CreateSubStyleWithClass() is passing in null to gtk_style_context_get_path?

Comment 1

[Thinker Li [:sinker]]

Hi Emilio,
This bug seems relating to bug 1973702.
CreateWidget() in GtkWidgets.cpp return nullptr for Type::ScrollbarThumb.
According to the crash report, nsLookAndFeel::PerThemeData::Init() [1] on the stack will cause calling CreateWidget() with this type.
It eventually calls gtk_style_context_get_path() passing NULL as an argument, causing the crash.
I have checked out the code of gtk-3.14.0 to check gtk_style_context_get_path(). The first thing it does is to dereference context it's argument.
That is NULL.

[1] https://hg-edge.mozilla.org/mozilla-central/file/8b0d004a4d3f03394d1e7072f95d95a65415a0dc/widget/gtk/nsLookAndFeel.cpp#l2216

Comment 2

[Emilio Cobos Álvarez [:emilio]]

Attachment: Bug 1978136 - Fix pre-gtk-3.20 codepath for scrollbar styling. r=stransky

This restores the pre-regression status. There's still other fatal
assertions if you hit this code-path but those don't hit on release
builds so I think we're ok.

Comment 3

[Emilio Cobos Álvarez [:emilio]]

Mike, given https://repology.org/project/gtk/versions, would it be fine to drop support for anything older than gtk 3.24 (or at least 3.20)?

It's clearly not getting any real testing, and all distros that package those are EOLd a while ago (Ubuntu 18.04 has 3.22 for example)

Comment 4

[Emilio Cobos Álvarez [:emilio]]

Comment on attachment 9502890 [details]
Bug 1978136 - Fix pre-gtk-3.20 codepath for scrollbar styling. r=stransky

Beta/Release Uplift Approval Request

• User impact if declined/Reason for urgency: Fixes startup crash with gtk versions we claim to support.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: none
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Fixes a typo in regressing bug.
• String changes made/needed: none
• Is Android affected?: No

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/f46dda8fd9fd
https://hg.mozilla.org/integration/autoland/rev/a0119a38620c
Fix pre-gtk-3.20 codepath for scrollbar styling. r=stransky

Comment 6

[Cristian Tuns]

https://hg.mozilla.org/mozilla-central/rev/a0119a38620c

Comment 7

[Dianna Smith [:diannaS]]

Comment on attachment 9502890 [details]
Bug 1978136 - Fix pre-gtk-3.20 codepath for scrollbar styling. r=stransky

Approved for 142.0b5

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/1a883f4c18b3
https://hg.mozilla.org/releases/mozilla-beta/rev/d07324026fa7
Fix pre-gtk-3.20 codepath for scrollbar styling. r=stransky,a=dsmith