[PATCH 13/13] drm: allow render capable master with DRM_AUTH ioctls

[Thomas Hellstrom]

On 5/27/19 3:16 PM, Daniel Vetter wrote:
> On Mon, May 27, 2019 at 02:39:18PM +0200, Thomas Hellstrom wrote:
>> On 5/27/19 10:17 AM, Emil Velikov wrote:
>>> From: Emil Velikov <emil.velikov at collabora.com>
>>>
>>> There are cases (in mesa and applications) where one would open the
>>> primary node without properly authenticating the client.
>>>
>>> Sometimes we don't check if the authentication succeeds, but there's
>>> also cases we simply forget to do it.
>>>
>>> The former was a case for Mesa where it did not not check the return
>>> value of drmGetMagic() [1]. That was fixed recently although, there's
>>> the question of older drivers or other apps that exbibit this behaviour.
>>>
>>> While omitting the call results in issues as seen in [2] and [3].
>>>
>>> In the libva case, libva itself doesn't authenticate the DRM client and
>>> the vaGetDisplayDRM documentation doesn't mention if the app should
>>> either.
>>>
>>> As of today, the official vainfo utility doesn't authenticate.
>>>
>>> To workaround issues like these, some users resort to running their apps
>>> under sudo. Which admittedly isn't always a good idea.
>>>
>>> Since any DRIVER_RENDER driver has sufficient isolation between clients,
>>> we can use that, for unauthenticated [primary node] ioctls that require
>>> DRM_AUTH. But only if the respective ioctl is tagged as DRM_RENDER_ALLOW.
>>>
>>> v2:
>>> - Rework/simplify if check (Daniel V)
>>> - Add examples to commit messages, elaborate. (Daniel V)
>>>
>>> v3:
>>> - Use single unlikely (Daniel V)
>>>
>>> v4:
>>> - Patch was reverted because it broke AMDGPU, apply again. The AMDGPU
>>> issue is fixed with earlier patch.
>>>
>>> [1] https://gitlab.freedesktop.org/mesa/mesa/blob/2bc1f5c2e70fe3b4d41f060af9859bc2a94c5b62/src/egl/drivers/dri2/platform_wayland.c#L1136
>>> [2] https://lists.freedesktop.org/archives/libva/2016-July/004185.html
>>> [3] https://gitlab.freedesktop.org/mesa/kmscube/issues/1
>>> Testcase: igt/core_unauth_vs_render
>>> Cc: intel-gfx at lists.freedesktop.org
>>> Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
>>> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
>>> Link: https://patchwork.freedesktop.org/patch/msgid/20190114085408.15933-2-emil.l.velikov@gmail.com
>>> ---
>>>    drivers/gpu/drm/drm_ioctl.c | 20 ++++++++++++++++----
>>>    1 file changed, 16 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
>>> index 9841c0076f02..b64b022a2b29 100644
>>> --- a/drivers/gpu/drm/drm_ioctl.c
>>> +++ b/drivers/gpu/drm/drm_ioctl.c
>>> @@ -511,6 +511,13 @@ int drm_version(struct drm_device *dev, void *data,
>>>    	return err;
>>>    }
>>> +static inline bool
>>> +drm_render_driver_and_ioctl(const struct drm_device *dev, u32 flags)
>>> +{
>>> +	return drm_core_check_feature(dev, DRIVER_RENDER) &&
>>> +		(flags & DRM_RENDER_ALLOW);
>>> +}
>>> +
>>>    /**
>>>     * drm_ioctl_permit - Check ioctl permissions against caller
>>>     *
>>> @@ -525,14 +532,19 @@ int drm_version(struct drm_device *dev, void *data,
>>>     */
>>>    int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
>>>    {
>>> +	const struct drm_device *dev = file_priv->minor->dev;
>>> +
>>>    	/* ROOT_ONLY is only for CAP_SYS_ADMIN */
>>>    	if (unlikely((flags & DRM_ROOT_ONLY) && !capable(CAP_SYS_ADMIN)))
>>>    		return -EACCES;
>>> -	/* AUTH is only for authenticated or render client */
>>> -	if (unlikely((flags & DRM_AUTH) && !drm_is_render_client(file_priv) &&
>>> -		     !file_priv->authenticated))
>>> -		return -EACCES;
>>> +	/* AUTH is only for master ... */
>>> +	if (unlikely((flags & DRM_AUTH) && drm_is_primary_client(file_priv))) {
>>> +		/* authenticated ones, or render capable on DRM_RENDER_ALLOW. */
>>> +		if (!file_priv->authenticated &&
>>> +		    !drm_render_driver_and_ioctl(dev, flags))
>>> +			return -EACCES;
>>> +	}
>> This breaks vmwgfx primary client authentication in the surface_reference
>> ioctl, which takes different paths in case of render clients and primary
>> clients, but adding an auth check in the primary path in the vmwgfx code
>> should fix this.
> Hm yeah we need to adjust that ... otoh kinda not sure why this is gated
> on authentication status, and not on "am I master or not" status. At least
> from a very cursory read ...
> -Daniel

The code snippet in question is:


         if (drm_is_primary_client(file_priv) &&
             user_srf->master != file_priv->master) {
             DRM_ERROR("Trying to reference surface outside of"
                   " master domain.\n");
             ret = -EACCES;
             goto out_bad_resource;
         }


In gem term's this means a client can't open a surface that hasn't been 
flinked by a client in the same master realm: You can't read from 
resources belonging to another X server's clients....

/Thomas



>
>> /Thomas
>>
>>
>>>    	/* MASTER is only for master or control clients */
>>>    	if (unlikely((flags & DRM_MASTER) &&
>>
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