linux-kernel - [PATCH 3.2 026/221] tty: Prevent untrappable signals from malicious program

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Date:	Tue, 05 May 2015 02:16:39 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"One Thousand Gnomes" <gnomes@...rguk.ukuu.org.uk>,
	"Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
	"Peter Hurley" <peter@...leysoftware.com>,
	"Jiri Slaby" <jslaby@...e.cz>, "Theodore Ts'o" <tytso@....edu>,
	"Howard Chu" <hyc@...as.com>
Subject: [PATCH 3.2 026/221] tty: Prevent untrappable signals from
 malicious program

3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Hurley <peter@...leysoftware.com>

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@....edu>
Cc: Howard Chu <hyc@...as.com>
Cc: One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby@...e.cz>
Signed-off-by: Peter Hurley <peter@...leysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/tty/pty.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -175,6 +175,9 @@ static int pty_signal(struct tty_struct
 	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);

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