[3.13.y-ckt stable] Patch "tty: Prevent untrappable signals from malicious program" 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: Prevent untrappable signals from malicious program

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-ckt18.

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 25274763f7fd47fe90013cc117ab1ccc6e5f7686 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter at hurleysoftware.com>
Date: Mon, 19 Jan 2015 13:05:03 -0500
Subject: tty: Prevent untrappable signals from malicious program

commit 37480a05685ed5b8e1b9bf5e5c53b5810258b149 upstream.

Commit 26df6d13406d1a5 ("tty: Add EXTPROC support for LINEMODE")
allows a process which has opened a pty master to send _any_ signal
to the process group of the pty slave. Although potentially
exploitable by a malicious program running a setuid program on
a pty slave, it's unknown if this exploit currently exists.

Limit to signals actually used.

Cc: Theodore Ts'o <tytso at mit.edu>
Cc: Howard Chu <hyc at symas.com>
Cc: One Thousand Gnomes <gnomes at lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby at suse.cz>
Signed-off-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/pty.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 25c9bc7..e49616e 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -209,6 +209,9 @@ static int pty_signal(struct tty_struct *tty, int sig)
 	unsigned long flags;
 	struct pid *pgrp;

+	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
+		return -EINVAL;
+
 	if (tty->link) {
 		spin_lock_irqsave(&tty->link->ctrl_lock, flags);
 		pgrp = get_pid(tty->link->pgrp);
--
1.9.1