FROMGIT: binder: make sure fd closes complete

During BC_FREE_BUFFER processing, the BINDER_TYPE_FDA object
cleanup may close 1 or more fds. The close operations are
completed using the task work mechanism -- which means the thread
needs to return to userspace or the file object may never be
dereferenced -- which can lead to hung processes.

Force the binder thread back to userspace if an fd is closed during
BC_FREE_BUFFER handling.

Fixes: 80cd7956 ("binder: fix use-after-free due to ksys_close() during fdget()")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Martijn Coenen <maco@android.com>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Todd Kjos <tkjos@google.com>
Link: https://lore.kernel.org/r/20210830195146.587206-1-tkjos@google.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 111997867
(cherry picked from commit 5fdb55c1ac9585eb23bb2541d5819224429e103d
 git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git
Change-Id: Idffa9b54edfc289d95b24f7ae2aa11ae494c7158