From: Peter Hurley <peter@hurleysoftware.com>
Date: Wed, 10 Sep 2014 19:06:35 +0000 (-0400)
Subject: tty: Hold termios_rwsem for tcflow(TCIxxx)
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=c274f6ef1c6665632767d32e4ab912aad839ce27;p=linux-beck.git

tty: Hold termios_rwsem for tcflow(TCIxxx)

While transmitting a START/STOP char for tcflow(TCION/TCIOFF), prevent
a termios change. Otherwise, a garbage in-band flow control char
may be sent, if the termios change overlaps the transmission setup.

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 ad9120d1c0f1..62380ccf70fb 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -1164,17 +1164,21 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
 			spin_unlock_irq(&tty->flow_lock);
 			break;
 		case TCIOFF:
+			down_read(&tty->termios_rwsem);
 			if (STOP_CHAR(tty) != __DISABLED_CHAR)
-				return tty_send_xchar(tty, STOP_CHAR(tty));
+				retval = tty_send_xchar(tty, STOP_CHAR(tty));
+			up_read(&tty->termios_rwsem);
 			break;
 		case TCION:
+			down_read(&tty->termios_rwsem);
 			if (START_CHAR(tty) != __DISABLED_CHAR)
-				return tty_send_xchar(tty, START_CHAR(tty));
+				retval = tty_send_xchar(tty, START_CHAR(tty));
+			up_read(&tty->termios_rwsem);
 			break;
 		default:
 			return -EINVAL;
 		}
-		return 0;
+		return retval;
 	case TCFLSH:
 		retval = tty_check_change(tty);
 		if (retval)