[PATCH 14/19] present: Add window flip mode

Michel Dänzer michel at daenzer.net
Tue Feb 6 11:19:06 UTC 2018

On 2018-02-05 08:09 PM, Keith Packard wrote:
> Michel Dänzer <michel at daenzer.net> writes:
>> Ignoring the Security extension, the client has the same control over
>> the contents of another application's window *using* the X protocol,
>> doesn't it?
> Yeah, good point -- it could easily call DRI3BufferFromPixmap for the
> window pixmap and have exactly the same access.

Or simply draw to the window using X11 requests.

>> If this is a concern, Present could try allocating a new window pixmap
>> to unflip to, and just leave the last flip pixmap as the window pixmap
>> if that fails (which it "never" will, in basically any scenario where
>> the X server can otherwise continue working normally).
> Given your point above, I can't think of any reason to not just use the
> provided pixmap as the window pixmap. It does mean we'll be trusting
> that the application doesn't accidentally re-use the buffer at some
> later time, but as you say, there's no actual security benefit.

In the vast majority of cases, it'll be the application's own window
anyway, so even accidents won't affect anything else. :)

Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer

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