[ 3.5.y.z extended stable ] Patch "TTY: do not reset master's packet mode" has been added to staging queue

[Luis Henriques]

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

    TTY: do not reset master's packet mode

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2b3005ef91c8aa3dff46ac59e2789e51aebefc81 Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby at suse.cz>
Date: Tue, 15 Jan 2013 23:26:22 +0100
Subject: [PATCH] TTY: do not reset master's packet mode

commit b81273a132177edd806476b953f6afeb17b786d5 upstream.

Now that login from util-linux is forced to drop all references to a
TTY which it wants to hangup (to reach reference count 1) we are
seeing issues with telnet. When login closes its last reference to the
slave PTY, it also resets packet mode on the *master* side. And we
have a race here.

What telnet does is fork+exec of `login'. Then there are two
scenarios:
* `login' closes the slave TTY and resets thus master's packet mode,
  but even now telnet properly sets the mode, or
* `telnetd' sets packet mode on the master, `login' closes the slave
  TTY and resets master's packet mode.

The former case is OK. However the latter happens in much more cases,
by the order of magnitude to be precise. So when one tries to login to
such a messed telnet setup, they see the following:
inux login:
            ogin incorrect

Note the missing first letters -- telnet thinks it is still in the
packet mode, so when it receives "linux login" from `login', it
considers "l" as the type of the packet and strips it.

SuS does not mention how the implementation should behave. Both BSDs I
checked (Free and Net) do not reset the flag upon the last close.

By this I am resurrecting an old bug, see References. We are hitting
it regularly now, i.e. with updated util-linux, ergo login.

Here, I am changing a behavior introduced back in 2.1 times. It would
better have a long time testing before goes upstream.

Signed-off-by: Jiri Slaby <jslaby at suse.cz>
Cc: Mauro Carvalho Chehab <mchehab at redhat.com>
Cc: Bryan Mason <bmason at redhat.com>
References: https://lkml.org/lkml/2009/11/11/223
References: https://bugzilla.redhat.com/show_bug.cgi?id=504703
References: https://bugzilla.novell.com/show_bug.cgi?id=797042
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/tty/pty.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 5505ffc..ce53594 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -49,7 +49,6 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	tty->packet = 0;
 	if (!tty->link)
 		return;
-	tty->link->packet = 0;
 	set_bit(TTY_OTHER_CLOSED, &tty->link->flags);
 	wake_up_interruptible(&tty->link->read_wait);
 	wake_up_interruptible(&tty->link->write_wait);
--
1.8.1.2