Hi, On Thu, Nov 01, 2018 at 12:24:47AM +0000, Dmitry Safonov wrote: > tty_ldisc_reinit() doesn't race with neither tty_ldisc_hangup() > nor set_ldisc() nor tty_ldisc_release() as they use tty lock. > But it races with anyone who expects line discipline to be the same > after hoding read semaphore in tty_ldisc_ref(). > > We've seen the following crash on v4.9.108 stable: > > BUG: unable to handle kernel paging request at 0000000000002260 > IP: [..] n_tty_receive_buf_common+0x5f/0x86d > Workqueue: events_unbound flush_to_ldisc > Call Trace: > [..] n_tty_receive_buf2 > [..] tty_ldisc_receive_buf > [..] flush_to_ldisc > [..] process_one_work > [..] worker_thread > [..] kthread > [..] ret_from_fork > > tty_ldisc_reinit() should be called with ldisc_sem hold for writing, > which will protect any reader against line discipline changes. > > Cc: Greg Kroah-Hartman <[email protected]> > Cc: Jiri Slaby <[email protected]> > Cc: [email protected] # b027e2298bd5 ("tty: fix data race between > tty_init_dev and flush of buf") > Reviewed-by: Jiri Slaby <[email protected]> > Reported-by: [email protected] > Tested-by: Mark Rutland <[email protected]> > Tested-by: Tetsuo Handa <[email protected]>
Feel free to add Tested-by: Tycho Andersen <[email protected]> to this as well. We've recently seen this bug (well, the one that syzbot reported), and this patch fixes it. Tycho
