fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free
In the Linux kernel, the following vulnerability has been resolved:
fuse: wait for FR_FINISHED on abort_on_kill to prevent use-after-free
The abort_on_kill path in request_wait_answer() calls fuse_abort_conn()
and returns without waiting for FR_FINISHED. If fuse_dev_do_write() is
concurrently processing the same request (FR_LOCKED set), the caller
frees req->args while it is still being accessed, causing a
use-after-free.
Fix this by jumping to the existing wait_event(FR_FINISHED) instead of
returning early. The wait will not hang because fuse_abort_conn()
ensures all requests are ended.
