From 2622d73e51acfe1dbeb21bf2299066bdead85163 Mon Sep 17 00:00:00 2001 From: Peter Hurley Date: Thu, 16 Oct 2014 15:33:27 -0400 Subject: [PATCH] pty: Fix packet mode setting race Because pty_set_pktmode() does not claim the slave's ctrl_lock to clear ->ctrl_status (to avoid unnecessary lock nesting), pty_set_pktmode() may accidentally erase new ->ctrl_status updates. For example, CPU 0 | CPU 1 pty_set_pktmode() | pty_start() spin_lock(master's ctrl_lock) | tty->packet = 1 | | if (tty->link->packet) | spin_lock(slave's ctrl_lock) | tty->ctrl_status = TIOCPKT_START tty->link->ctrl_status = 0 | Ensure the clear of ->ctrl_status occurs before packet mode is set (and observable on another cpu). Signed-off-by: Peter Hurley Reviewed-by: Alan Cox Signed-off-by: Greg Kroah-Hartman --- drivers/tty/pty.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index e554393d5551..bcec4c71a408 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -186,8 +186,9 @@ static int pty_set_pktmode(struct tty_struct *tty, int __user *arg) spin_lock_irq(&tty->ctrl_lock); if (pktmode) { if (!tty->packet) { - tty->packet = 1; tty->link->ctrl_status = 0; + smp_mb(); + tty->packet = 1; } } else tty->packet = 0;