In the Linux kernel, the following vulnerability has been resolved:
io_uring/openclose: keep the lock in io_pipe_fixed()
io_pipe_fixed() installs both ends of the pipe in the fixed file table,
drops ->uring_lock, and copies the slot numbers to the application. If
that faults, it takes the lock again and removes whatever is in these
slots.
If the request is run by io-wq the lock really is dropped in between, and
the slots are visible to everybody else. By the time the error path gets
to them, they may have been closed and reused, by IORING_OP_CLOSE and a
direct open or accept, or by IORING_REGISTER_FILES_UPDATE. Then a file is
removed from the table that has nothing to do with the failed request.
Do the copy with the lock held. Faulting in user memory under
->uring_lock is fine, the registration paths do it all the time.