[PATCH xserver] xwayland: avoid a crash with empty window pixmaps

[Olivier Fourdan]

Hi Daniel,

On Thu, Jan 18, 2018 at 12:22 PM, Daniel Stone <daniel at fooishbar.org> wrote:

> Odd; how could we have a realized 0x0 window which also has damage? I
>

Hehe, yeap, I had the same question, but didn't find the answer... :)


> wonder if this isn't actually a UAF where the xwl_window has since
> been unrealized, in which case you should be able to reproduce pretty
> easily by causing damage on a window and then immediately destroying
> it. In that case, we just need
> wl_list_remove(&xwl_window->link_damage) inside
> xwl_window_unrealize().
>

But we do already do an “xorg_list_del(&xwl_window->link_damage);” in
xwl_window_unrealize()

However, we do that only if xwl_window is a thing and the damage region is
not empty:

https://cgit.freedesktop.org/xorg/xserver/tree/hw/xwayland/xwayland.c#n583

Weird...

Cheers,
Olivier
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