[3.13.y-ckt stable] Patch "TTY: fix tty_wait_until_sent on 64-bit machines" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    TTY: fix tty_wait_until_sent on 64-bit machines

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 16f581e04ae91cf51a543b69349c6c8b4b1c247a Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan at kernel.org>
Date: Wed, 4 Mar 2015 10:39:06 +0100
Subject: TTY: fix tty_wait_until_sent on 64-bit machines

commit 79fbf4a550ed6a22e1ae1516113e6c7fa5d56a53 upstream.

Fix overflow bug in tty_wait_until_sent on 64-bit machines, where an
infinite timeout (0) would be passed to the underlying tty-driver's
wait_until_sent-operation as a negative timeout (-1), causing it to
return immediately.

This manifests itself for example as tcdrain() returning immediately,
drivers not honouring the drain flags when setting terminal attributes,
or even dropped data on close as a requested infinite closing-wait
timeout would be ignored.

The first symptom  was reported by Asier LLANO who noted that tcdrain()
returned prematurely when using the ftdi_sio usb-serial driver.

Fix this by passing 0 rather than MAX_SCHEDULE_TIMEOUT (LONG_MAX) to the
underlying tty driver.

Note that the serial-core wait_until_sent-implementation is not affected
by this bug due to a lucky chance (comparison to an unsigned maximum
timeout), and neither is the cyclades one that had an explicit check for
negative timeouts, but all other tty drivers appear to be affected.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: ZIV-Asier Llano Palacios <asier.llano at cgglobal.com>
Signed-off-by: Johan Hovold <johan at kernel.org>
Reviewed-by: Peter Hurley <peter at hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/tty/tty_ioctl.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/tty_ioctl.c b/drivers/tty/tty_ioctl.c
index 6fd60fe..22da05d 100644
--- a/drivers/tty/tty_ioctl.c
+++ b/drivers/tty/tty_ioctl.c
@@ -217,11 +217,17 @@ void tty_wait_until_sent(struct tty_struct *tty, long timeout)
 #endif
 	if (!timeout)
 		timeout = MAX_SCHEDULE_TIMEOUT;
+
 	if (wait_event_interruptible_timeout(tty->write_wait,
-			!tty_chars_in_buffer(tty), timeout) >= 0) {
-		if (tty->ops->wait_until_sent)
-			tty->ops->wait_until_sent(tty, timeout);
+			!tty_chars_in_buffer(tty), timeout) < 0) {
+		return;
 	}
+
+	if (timeout == MAX_SCHEDULE_TIMEOUT)
+		timeout = 0;
+
+	if (tty->ops->wait_until_sent)
+		tty->ops->wait_until_sent(tty, timeout);
 }
 EXPORT_SYMBOL(tty_wait_until_sent);

--
1.9.1