[PATCH] render: Avoid infinite loops in alpha map handling (#23581)

[Adam Jackson]

On Fri, 2010-05-21 at 09:08 -0700, Keith Packard wrote:
> On Tue, 11 May 2010 14:12:52 -0400, Adam Jackson <ajax at nwnk.net> wrote:
> 
> > I just want it to not trivially crash my server.  I could care less
> > about correctness for this.
> 
> How about this?
> 
> From 50be5e8ff00e734506d2bb0c25054d7648f0cf1e Mon Sep 17 00:00:00 2001
> From: Keith Packard <keithp at keithp.com>
> Date: Fri, 21 May 2010 09:01:43 -0700
> Subject: [PATCH] Don't let alpha maps recurse in fb. Bug 23581.
> 
> Recursive alpha maps (where one picture's alpha map is set to a
> picture with an external alpha map) would be all fine and dandy,
> except for the case where the client constructs a loop. Detecting this
> case when setting the alpha map values would be difficult as any time
> an alpha map is set, the server would have to check for the looping
> case.
> 
> Instead, a far simpler fix is to simply disallow recursive alpha maps
> in the rendering code, the Render spec is ambiguous in this area and
> allows us to to ignore the recursive case.
> 
> Signed-off-by: Keith Packard <keithp at keithp.com>

Reviewed-by: Adam Jackson <ajax at redhat.com>

I'll update the Render spec to explicitly make this undefined, since we
need to do a new release for the 7.6 katamari.  Please do apply this for
xserver 1.9.

- ajax
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