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

[Emil Velikov <emil.l.velikov@gmail.com>]

On 2019/05/27, Thomas Hellstrom wrote:
> On 5/27/19 10:17 AM, Emil Velikov wrote:
> > From: Emil Velikov <emil.velikov@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@lists.freedesktop.org
> > Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
> > Reviewed-by: Daniel Vetter <daniel.vetter@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.
> 
Ack. Thanks for having a look. Will include a permission check in v2
of the series.

-Emil
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