linux-kernel - [PATCH 3.12 038/175] tty: Prevent untrappable signals from malicious program

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Message-Id: <09179f19a3a7b87482925384ef1c21af546b8910.1426581621.git.jslaby@suse.cz>
Date:	Tue, 17 Mar 2015 09:40:16 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Hurley <peter@...leysoftware.com>,
	Theodore Ts'o <tytso@....edu>, Howard Chu <hyc@...as.com>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 038/175] tty: Prevent untrappable signals from malicious program

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/pty.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index 25c9bc783722..e49616eeb1cc 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);
-- 
2.3.0

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