From 37480a05685ed5b8e1b9bf5e5c53b5810258b149 Mon Sep 17 00:00:00 2001
From: Peter Hurley <peter@hurleysoftware.com>
Date: Mon, 19 Jan 2015 13:05:03 -0500
Subject: [PATCH] tty: Prevent untrappable signals from malicious program

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@mit.edu>
Cc: Howard Chu <hyc@symas.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: <stable@vger.kernel.org> # 2.6.36+
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/pty.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index a9d256d6e909..6e1f1505f04e 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -210,6 +210,9 @@ static int pty_signal(struct tty_struct *tty, int sig)
 {
 	struct pid *pgrp;
 
+	if (sig != SIGINT && sig != SIGQUIT && sig != SIGTSTP)
+		return -EINVAL;
+
 	if (tty->link) {
 		pgrp = tty_get_pgrp(tty->link);
 		if (pgrp)
-- 
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