tty: Fix SIGTTOU not sent with tcflush()

Commit '3b92e7bf4661e7bb2610b5b12137ba8158b6ca11'
  tty: Fix recursive deadlock in tty_perform_flush()
introduced a regression where tcflush() does not generate
SIGTTOU for background process groups.

Make sure ioctl(TCFLSH) calls tty_check_change() when
invoked from the line discipline.

Cc: stable@vger.kernel.org # v3.10+
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 03ba081c577251a0947466b79f23b36b359b51c1..6fd60fece6b4b01684695b7df4af376e695ff873 100644 (file)
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1201,6 +1201,9 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
                }
                return 0;
        case TCFLSH:
+               retval = tty_check_change(tty);
+               if (retval)
+                       return retval;
                return __tty_perform_flush(tty, arg);
        default:
                /* Try the mode commands */