On Wed, 2018-08-29 at 13:34 +0900, Sergey Senozhatsky wrote:
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:
This is too old for me to remember buit yes, there definitely was a bug there...
@@ -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