CVE-2021-47360: Unchecked Return Value

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

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.