On Thu, Aug 26, 2021 at 07:53:58PM +0800, Desmond Cheong Zhi Xi wrote:
> On 26/8/21 5:53 pm, Daniel Vetter wrote:
> > On Thu, Aug 26, 2021 at 10:01:16AM +0800, Desmond Cheong Zhi Xi wrote:
> > > drm_master_release can be called on a drm_file without a master, which
> > > results in a null ptr dereference of file_priv->master->magic_map. The
> > > three cases are:
> > >
> > > 1. Error path in drm_open_helper
> > > drm_open():
> > > drm_open_helper():
> > > drm_master_open():
> > > drm_new_set_master(); <--- returns -ENOMEM,
> > > drm_file.master not set
> > > drm_file_free():
> > > drm_master_release(); <--- NULL ptr dereference
> > > (file_priv->master->magic_map)
> > >
> > > 2. Error path in mock_drm_getfile
> > > mock_drm_getfile():
> > > anon_inode_getfile(); <--- returns error, drm_file.master not set
> > > drm_file_free():
> > > drm_master_release(); <--- NULL ptr dereference
> > > (file_priv->master->magic_map)
> > >
> > > 3. In drm_client_close, as drm_client_open doesn't set up a master
> > >
> > > drm_file.master is set up in drm_open_helper through the call to
> > > drm_master_open, so we mirror it with a call to drm_master_release in
> > > drm_close_helper, and remove drm_master_release from drm_file_free to
> > > avoid the null ptr dereference.
> > >
> > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
> >
> > Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> >
> > I guess we should also have a cc: stable on this one? I think this bug
> > existed since pretty much forever, but maybe more prominent with the
> > drm_client stuff added a while ago.
> > -Daniel
> >
>
> Thanks for the reviews, Daniel.
>
> Took a closer look. I think if we cc: stable, this fix should accompany
> commit 7eeaeb90a6a5 ("drm/file: Don't set master on in-kernel clients")
> which moves the drm_master_open out from drm_file_alloc into
> drm_open_helper.
Ah right, please reference that commit with a Fixes: line.
-Daniel
>
> > > ---
> > > drivers/gpu/drm/drm_file.c | 6 +++---
> > > 1 file changed, 3 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> > > index ed25168619fc..90b62f360da1 100644
> > > --- a/drivers/gpu/drm/drm_file.c
> > > +++ b/drivers/gpu/drm/drm_file.c
> > > @@ -282,9 +282,6 @@ void drm_file_free(struct drm_file *file)
> > > drm_legacy_ctxbitmap_flush(dev, file);
> > > - if (drm_is_primary_client(file))
> > > - drm_master_release(file);
> > > -
> > > if (dev->driver->postclose)
> > > dev->driver->postclose(dev, file);
> > > @@ -305,6 +302,9 @@ static void drm_close_helper(struct file *filp)
> > > list_del(&file_priv->lhead);
> > > mutex_unlock(&dev->filelist_mutex);
> > > + if (drm_is_primary_client(file_priv))
> > > + drm_master_release(file_priv);
> > > +
> > > drm_file_free(file_priv);
> > > }
> > > --
> > > 2.25.1
> > >
> >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
