Commit 83d817f4 authored by Dmitry Safonov's avatar Dmitry Safonov Committed by Greg Kroah-Hartman
Browse files

tty: Hold tty_ldisc_lock() during tty_reopen()

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: Jiri Slaby <>
Cc: # b027e229

 ("tty: fix data race between tty_init_dev and flush of buf")
Reviewed-by: default avatarJiri Slaby <>
Tested-by: Mark Rutland's avatarMark Rutland <>
Tested-by: default avatarTetsuo Handa <>
Signed-off-by: default avatarDmitry Safonov <>
Tested-by: default avatarTycho Andersen <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 231f8fd0
......@@ -1268,15 +1268,20 @@ static int tty_reopen(struct tty_struct *tty)
if (test_bit(TTY_EXCLUSIVE, &tty->flags) && !capable(CAP_SYS_ADMIN))
return -EBUSY;
retval = tty_ldisc_lock(tty, 5 * HZ);
if (retval)
return retval;
if (tty->ldisc)
return 0;
goto out_unlock;
retval = tty_ldisc_reinit(tty, tty->termios.c_line);
if (retval)
return retval;
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