Hi, Cc-ing Benjamin on this.
On (08/29/18 03:23), Dmitry Safonov wrote: > 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 Seems that you are not the first one to hit this NULL deref. > I think, tty_ldisc_reinit() should be called with ldisc_sem hold for > writing, which will protect any reader against line discipline changes. Per https://lore.kernel.org/patchwork/patch/777220/ : Note that we noticed one path that called reinit without the ldisc lock : held for writing, we added that, but it didn't fix the problem. And I guess that Ben meant the same reinit path which you patched: > @@ -1267,15 +1267,20 @@ static int tty_reopen(struct tty_struct *tty) > if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN)) > return -EBUSY; > > - tty->count++; > + retval = tty_ldisc_lock(tty, 5 * HZ); > + if (retval) > + return retval; > > + tty->count++; > if (tty->ldisc) > - return 0; > + goto out_unlock; > > retval = tty_ldisc_reinit(tty, tty->termios.c_line); > if (retval) > tty->count--; > > +out_unlock: > + tty_ldisc_unlock(tty); > return retval; > } -ss
