• Al Viro's avatar
    fix io_destroy()/aio_complete() race · f01d1b57
    Al Viro authored
    commit 4faa9996 upstream.
    
    If io_destroy() gets to cancelling everything that can be cancelled and
    gets to kiocb_cancel() calling the function driver has left in ->ki_cancel,
    it becomes vulnerable to a race with IO completion.  At that point req
    is already taken off the list and aio_complete() does *NOT* spin until
    we (in free_ioctx_users()) releases ->ctx_lock.  As the result, it proceeds
    to kiocb_free(), freing req just it gets passed to ->ki_cancel().
    
    Fix is simple - remove from the list after the call of kiocb_cancel().  All
    instances of ->ki_cancel() already have to cope with the being called with
    iocb still on list - that's what happens in io_cancel(2).
    
    Cc: stable@kernel.org
    Fixes: 0460fef2 "aio: use cancellation list lazily"
    Signed-off-by: 's avatarAl Viro <viro@zeniv.linux.org.uk>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    f01d1b57