tty: Prevent untrappable signals from malicious program

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>

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index abfd9908978188ffe3bfd7a9c3aa3e8c6700c5d9..7cb36813aac2bbded76575f36620d4ec510b1a98 100644 (file)
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -215,6 +215,9 @@ 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);