CVE-2021-47533

In the Linux kernel, the following vulnerability has been resolved:

drm/vc4: kms: Clear the HVS FIFO commit pointer once done

Commit 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a

commit") introduced a wait on the previous commit done on a given HVS

FIFO.

However, we never cleared that pointer once done. Since

drm_crtc_commit_put can free the drm_crtc_commit structure directly if

we were the last user, this means that it can lead to a use-after free

if we were to duplicate the state, and that stale pointer would even be

copied to the new state.

Set the pointer to NULL once we're done with the wait so that we don't

carry over a pointer to a free'd structure.