[PATCH] drm: Fix an unwanted master inheritance

[Daniel Vetter]

On Tue, Dec 01, 2015 at 12:58:13PM +0100, Thomas Hellstrom wrote:
> On 12/01/2015 11:57 AM, Emil Velikov wrote:
> > Hi Thomas,
> >
> > Something doesn't feel quite right, please read on.
> >
> > On 30 November 2015 at 12:44, Thomas Hellstrom <thellstrom at vmware.com> wrote:
> >> A client calling drmSetMaster() using a file descriptor that was opened
> >> when another client was master would inherit the latter client's master
> >> object and all it's authenticated clients.
> >>
> >> This is unwanted behaviour, and when this happens, instead allocate a
> >> brand new master object for the client calling drmSetMaster().
> >>
> >> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> >> ---
> >>  drivers/gpu/drm/drm_drv.c  | 12 +++++++
> >>  drivers/gpu/drm/drm_fops.c | 80 ++++++++++++++++++++++++++++++----------------
> >>  include/drm/drmP.h         |  6 ++++
> >>  3 files changed, 70 insertions(+), 28 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> >> index 9362609..1f072ba 100644
> >> --- a/drivers/gpu/drm/drm_drv.c
> >> +++ b/drivers/gpu/drm/drm_drv.c
> >> @@ -160,6 +160,18 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
> >>                 goto out_unlock;
> >>         }
> >>
> >> +       if (!file_priv->allowed_master) {
> >> +               struct drm_master *saved_master = file_priv->master;
> >> +
> >> +               ret = drm_new_set_master(dev, file_priv);
> >> +               if (ret)
> >> +                       file_priv->master = saved_master;
> > Imho this shouldn'e belong here but in drm_new_set_master() - i.e. it
> > should unwind things on error. Similarly, although we restore the old
> > drm_master (below), we still have is_master, allowed_master and
> > authenticated set. Thus one can reuse the elevated credentials (is
> > this the right terminology?) despite that the ioctl has failed.
> >
> >> +               else
> >> +                       drm_master_put(&saved_master);
> >> +
> >> +               goto out_unlock;
> >> +       }
> >> +
> >>         file_priv->minor->master = drm_master_get(file_priv->master);
> >>         file_priv->is_master = 1;
> >>         if (dev->driver->master_set) {
> >> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
> >> index c59ce4d..4b5c11c 100644
> >> --- a/drivers/gpu/drm/drm_fops.c
> >> +++ b/drivers/gpu/drm/drm_fops.c
> >> @@ -126,6 +126,56 @@ static int drm_cpu_valid(void)
> >>  }
> >>
> >>  /**
> >> + * drm_new_set_master - Allocate a new master object and become master for the
> >> + * associated master realm.
> >> + *
> >> + * @dev: The associated device.
> >> + * @fpriv: File private identifying the client.
> >> + *
> >> + * This function must be called with dev::struct_mutex held. Returns negative
> >> + * error code on failure, zero on success.
> >> + */
> >> +int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
> >> +{
> >> +       int ret;
> >> +
> >> +       lockdep_assert_held_once(&dev->master_mutex);
> >> +       /* create a new master */
> >> +       fpriv->minor->master = drm_master_create(fpriv->minor);
> >> +       if (!fpriv->minor->master)
> >> +               return -ENOMEM;
> >> +
> >> +       fpriv->is_master = 1;
> >> +       fpriv->allowed_master = 1;
> >> +
> >> +       /* take another reference for the copy in the local file priv */
> >> +       fpriv->master = drm_master_get(fpriv->minor->master);
> >> +
> >> +       fpriv->authenticated = 1;
> >> +
> >> +       if (dev->driver->master_create) {
> >> +               ret = dev->driver->master_create(dev, fpriv->master);
> >> +               if (ret) {
> >> +                       /* drop both references if this fails */
> >> +                       drm_master_put(&fpriv->minor->master);
> >> +                       drm_master_put(&fpriv->master);
> >> +                       return ret;
> >> +               }
> >> +       }
> >> +       if (dev->driver->master_set) {
> >> +               ret = dev->driver->master_set(dev, fpriv, true);
> >> +               if (ret) {
> > Afaics both of these callbacks are available from legacy(UMS) drivers
> > aren't they ? With the radeon UMS removal patches in the works, this
> > leaves vmwgfx.
> >
> > Either way, perhaps we should set is_master, allowed_master and
> > authenticated after these two ? Or alternatively restore the original
> > values on error.
> >
> > Did I miss something or the above sounds about right ?
> It does. I'll address this and resend.

Just wanted to pull this in and noticed there's still this open. New
version incoming soon?

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch