[PATCH 3.4 020/172] tty: Prevent untrappable signals from malicious program

lizf
2015-06-16T08:40:36Z

From: Peter Hurley <peter@hurleysoftware.com>

3.4.108-rc1 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@mit.edu>
Cc: Howard Chu <hyc@symas.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
drivers/tty/pty.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index cf9a191..bc955d7 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -173,6 +173,9 @@ 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