[PATCH 3.16.y-ckt 070/183] tty: Prevent untrappable signals from malicious program

From: Luis Henriques
Date: Fri Mar 06 2015 - 05:38:40 EST

3.16.7-ckt8 -stable review patch. If anyone has any objections, please let me know.


From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>

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@xxxxxxx>
Cc: Howard Chu <hyc@xxxxxxxxx>
Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
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);
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