[Mesa-dev] [PATCH 1/3] egl/x11_dri3: disable WL_bind_wayland_display for devices without render nodes

[Michel Dänzer]

On 21.06.2016 15:24, Axel Davy wrote:
> On 21/06/2016 01:26, Michel Dänzer wrote:
>> On 20.06.2016 20:06, Frank Binns wrote:
>>> On 20/06/16 10:48, Michel Dänzer wrote:
>>>> On 18.06.2016 02:41, Frank Binns wrote:
>>>>> Up until now, DRI3 was only used for devices that have render nodes,
>>>>> unless
>>>>> overridden via an environment variable, with it falling back to DRI2
>>>>> otherwise.
>>>>> This limitation was there in order to support WL_bind_wayland_display
>>>>> as it
>>>>> requires client opened device node fds to be authenticated, which
>>>>> isn't possible
>>>>> when using DRI3. This is an unfortunate compromise as DRI3 provides
>>>>> security
>>>>> benefits over DRI2.
>>>> What exactly is it that works with render nodes but not with
>>>> unauthenticated non-render nodes? Isn't that a kernel bug?
>>> The problem isn't that something doesn't work with unauthenticated
>>> non-render nodes (wouldn't that be the kernel bug?) but that if a
>>> client opens the primary/legacy node it needs the resulting fd to
>>> be authenticated, which isn't supported by the X11 DRI3 protocol.
>> Authentication is required for using certain ioctls of non-render nodes.
>> It sounds like some ioctls are allowed to be used with render nodes but
>> not with unauthenticated non-render nodes, which seems like a kernel bug
>> — why would an ioctl be safe to use without authentication via a render
>> node but not via a non-render node?
>>
>> So, which ioctls required by WL_bind_wayland_display don't work with an
>> unauthenticated non-render node?
>>
>>
> The ioctl to authenticate is possible only when you have the master node
> (owned by the DDX when using X, or by the wayland compositor when using
> Wayland). There is only one master node.
> 
> 
> On of the motives of render-nodes is precisely to fix these limitations.

I understand all of that, but it doesn't answer my question. :)

Since WL_bind_wayland_display works with a render node, it means that
all ioctls it needs work without authentication when using a render
node. The question is, why do the same ioctls require authentication
when using a non-render node?


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