On 09/03/2018, 06:52 PM, 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 gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.com
Reviewed-by: Jiri Slaby jslaby@suse.cz
Cc: stable@vger.kernel.org # depends on commit b027e2298bd5 ("tty: fix data race between tty_init_dev and flush of buf") Reported-by: syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com Tested-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp Signed-off-by: Dmitry Safonov dima@arista.com
thanks,