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

[Adam Jackson]

On Thu, 2018-01-18 at 11:41 +0100, Olivier Fourdan wrote:
> This is a rare occurrence of a crash in Xwayland for which I don't have
> the reproducing steps, just a core file.
> 
> The backtrace looks as follow:
> 
>   #0  raise () from /usr/lib64/libc.so.6
>   #1  abort () from /usr/lib64/libc.so.6
>   #2  OsAbort () at utils.c:1361
>   #3  AbortServer () at log.c:877
>   #4  FatalError () at log.c:1015
>   #5  OsSigHandler () at osinit.c:154
>   #6  <signal handler called>
>   #7  xwl_glamor_pixmap_get_wl_buffer () at xwayland-glamor.c:162
>   #8  xwl_screen_post_damage () at xwayland.c:514
>   #9  block_handler () at xwayland.c:665
>   #10 BlockHandler () at dixutils.c:388
>   #11 WaitForSomething () at WaitFor.c:219
>   #12 Dispatch () at dispatch.c:422
>   #13 dix_main () at main.c:287
> 
> The crash is caused by dereferencing “xwl_pixmap->buffer” in
> xwl_glamor_pixmap_get_wl_buffer() because “xwl_pixmap” is NULL.
> 
> Reason for this is because the corresponding pixmap has a size of 0×0
> and no xwl_pixmap is created for pixmaps of size 0×0.

That can't really be the problem. X drawables are never 0x0.

- ajax