520790 - Qt build of Firefox or Fennec crashes whenever I visit a page featuring an iframe

Status: RESOLVED WONTFIX

(Core :: Graphics, defect)

Description

[James Cook]

User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.13) Gecko/2009080315 Ubuntu/9.04 (jaunty) Firefox/3.0.13
Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.3a1pre) Gecko/20091006 Minefield/3.7a1pre

Using the Qt build of Firefox or Fennec, whenever I visit a web page that features an iframe the browser crashes (segmentation fault).

Reproducible: Always

Steps to Reproduce:
1. Visit http://www.dyn-web.com/tutorials/iframes/basics.php.
2. If testing Firefox, scroll down a little bit.
Actual Results:  
The application crashes.

Expected Results:  
The application renders the web page.

The implementation of the Qt port has situations where a null pointer can be dereferenced, causing a segmentation fault.  This happens in gfx/cairo/cairo/src/cairo-qpainter-surface.cpp and the problem is caused by attempting to dereference the abstracted surface to get a pointer to the underlying QPainter.  In some situations, noted with the iframe case, the abstracted surface can be null.

Comment 1

[James Cook]

Attachment: A possible fix

A possible fix, checking that pointers to the abstracted surface's painter are allocated before dereferencing them.

Comment 2

[Tobias Hunger]

Comment on attachment 404838 [details] [diff] [review]
A possible fix

Seems sensible and does fix crashes for me.

Comment 3

[Mark Finkle (:mfinkle) (use needinfo?)]

Ok, but why is the QPainter null? Maybe we should fix that

Comment 4

[James Cook]

Attachment: A revision, cleaning up the unbalanced QPainter save and restore operations

Comment 5

[Doug Turner (:dougt)]

We agreed that we would not implement flush() in bug 498910.  498910's fix address this problem.

Comment 6

[Jeff Muizelaar [:jrmuizel]]

Comment on attachment 411410 [details] [diff] [review]
A revision, cleaning up the unbalanced QPainter save and restore operations

This shouldn't be needed anymore.