Messages in this thread | | | Subject | Re: [PATCH v8 1/7] drm: fix null ptr dereference in drm_master_release | From | Desmond Cheong Zhi Xi <> | Date | Thu, 26 Aug 2021 19:53:58 +0800 |
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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@gmail.com> > > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> > > 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.
>> --- >> 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 >> >
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