On Tue, Jan 19, 2021 at 02:08:12PM +0100, Christian König wrote:
> Am 19.01.21 um 14:03 schrieb Daniel Vetter:
> > While reviewing Christian's annotation patch I noticed that we have a
> > user-after-free for the WAIT_FOR_SUBMIT case: We drop the syncobj
> > reference before we've completed the waiting.
> >
> > Of course usually there's nothing bad happening here since userspace
> > keeps the reference, but we can't rely on userspace to play nice here!
> >
> > Signed-off-by: Daniel Vetter <[email protected]>
> > Fixes: bc9c80fe01a2 ("drm/syncobj: use the timeline point in
> > drm_syncobj_find_fence v4")
> > Cc: Christian König <[email protected]>
> > Cc: Lionel Landwerlin <[email protected]>
> > Cc: Maarten Lankhorst <[email protected]>
> > Cc: Maxime Ripard <[email protected]>
> > Cc: Thomas Zimmermann <[email protected]>
> > Cc: David Airlie <[email protected]>
> > Cc: Daniel Vetter <[email protected]>
> > Cc: [email protected]
> > Cc: <[email protected]> # v5.2+
>
> Reviewed-by: Christian König <[email protected]>
Pushed to drm-misc-fixes, thanks for reviewing.
-Daniel
>
> > ---
> > drivers/gpu/drm/drm_syncobj.c | 8 +++++---
> > 1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> > index 6e74e6745eca..349146049849 100644
> > --- a/drivers/gpu/drm/drm_syncobj.c
> > +++ b/drivers/gpu/drm/drm_syncobj.c
> > @@ -388,19 +388,18 @@ int drm_syncobj_find_fence(struct drm_file
> > *file_private,
> > return -ENOENT;
> > *fence = drm_syncobj_fence_get(syncobj);
> > - drm_syncobj_put(syncobj);
> > if (*fence) {
> > ret = dma_fence_chain_find_seqno(fence, point);
> > if (!ret)
> > - return 0;
> > + goto out;
> > dma_fence_put(*fence);
> > } else {
> > ret = -EINVAL;
> > }
> > if (!(flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT))
> > - return ret;
> > + goto out;
> > memset(&wait, 0, sizeof(wait));
> > wait.task = current;
> > @@ -432,6 +431,9 @@ int drm_syncobj_find_fence(struct drm_file
> > *file_private,
> > if (wait.node.next)
> > drm_syncobj_remove_wait(syncobj, &wait);
> > +out:
> > + drm_syncobj_put(syncobj);
> > +
> > return ret;
> > }
> > EXPORT_SYMBOL(drm_syncobj_find_fence);
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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