On Mon, Jul 27, 2020 at 05:54:59PM -0400, cohens@xxxxxxxxxxxxxx wrote: > On 2020-07-27 16:11, daniel@xxxxxxxx wrote: > > On Mon, Jul 27, 2020 at 09:55:07PM +0200, Greg KH wrote: > > > On Mon, Jul 20, 2020 at 06:30:50PM -0400, Steve Cohen wrote: > > > > A use-after-free in drm_gem_open_ioctl can happen if the > > > > GEM object handle is closed between the idr lookup and > > > > retrieving the size from said object since a local reference > > > > is not being held at that point. Hold the local reference > > > > while the object can still be accessed to fix this and > > > > plug the potential security hole. > > > > > > > > Signed-off-by: Steve Cohen <cohens@xxxxxxxxxxxxxx> > > > > --- > > > > drivers/gpu/drm/drm_gem.c | 10 ++++------ > > > > 1 file changed, 4 insertions(+), 6 deletions(-) > > > > > > > > diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c > > > > index 7bf628e..ee2058a 100644 > > > > --- a/drivers/gpu/drm/drm_gem.c > > > > +++ b/drivers/gpu/drm/drm_gem.c > > > > @@ -871,9 +871,6 @@ drm_gem_flink_ioctl(struct drm_device *dev, void *data, > > > > * @file_priv: drm file-private structure > > > > * > > > > * Open an object using the global name, returning a handle and the size. > > > > - * > > > > - * This handle (of course) holds a reference to the object, so the object > > > > - * will not go away until the handle is deleted. > > > > */ > > > > int > > > > drm_gem_open_ioctl(struct drm_device *dev, void *data, > > > > @@ -898,14 +895,15 @@ drm_gem_open_ioctl(struct drm_device *dev, void *data, > > > > > > > > /* drm_gem_handle_create_tail unlocks dev->object_name_lock. */ > > > > ret = drm_gem_handle_create_tail(file_priv, obj, &handle); > > > > - drm_gem_object_put_unlocked(obj); > > > > if (ret) > > > > - return ret; > > > > + goto err; > > > > > > > > args->handle = handle; > > > > args->size = obj->size; > > > > > > > > - return 0; > > > > +err: > > > > + drm_gem_object_put_unlocked(obj); > > > > + return ret; > > > > } > > > > > > > > /** > > > > > > As this seems to fix an important issue, any reason it wasn't cc: > > > stable > > > on it so that it gets backported properly? > > > > > > How about a "Fixes:" tag so that we know what commit id it fixes so we > > > know how far back to backport things? > > > > > > And a hint to the maintainers that "this is an issue that needs to get > > > into 5.8-final, it shouldn't wait around longer please" would have > > > also > > > been nice to see :) > > > > > > And what chagned from v1, aren't you supposed to list that somewhere > > > in > > > the changelog or below the --- line (never remember what DRM drivers > > > want here...) > > > > > > Care to send a v3? > > > > Don't worry, I'm pushing this to drm-misc-fixes now, should still make > > it > > to 5.8. Plus cc: stable. I didn't bother with Fixes: since I think the > > bug > > is rather old. Also, worst case you leak 32bit of some kernel memory > > that > > got reused already (but yeah I know that's often enough to get the foot > > in > > somewhere nasty and crack the door open). > > > > I think it fell through cracks because Sam said he'll apply, guess that > > didn't happen. > > Sam added his Reviewed-By on V1 with a comment to rename the goto label, > but in V2 I also updated the API documentation and the commit text for > a more complete change and thought he would re-add the tag. > > > Also yes a changelog, somewhere, for next time around. > > Apologies, it won't happen again. Should I still submit a V3? > It looks like you've got Greg's concerns covered. Uh no, but we need another patch to re-add the kerneldoc you deleted. I missed that when merging your patch. Also that's kinda what patch changelogs are for, for blind reviewers like me :-) -Daniel > > -Steve > > > -Daniel > > > > > > > > > > thanks, > > > > > > greg k-h -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
