linux-kernel - [PATCH v4] bluetooth: Fix WARNING in tty_set

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Date:   Sun,  3 Feb 2019 12:38:48 -0700
From:   Shuah Khan <shuah@...nel.org>
To:     marcel@...tmann.org, johan.hedberg@...il.com, johan@...nel.org,
        viro@...iv.linux.org.uk
Cc:     Shuah Khan <shuah@...nel.org>, linux-bluetooth@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4] bluetooth: Fix WARNING in tty_set_termios()

tty_set_termios() has the following WARN_ON which can be triggered with a
syscall to invoke TIOCSETD __NR_ioctl.

WARN_ON(tty->driver->type == TTY_DRIVER_TYPE_PTY &&
                tty->driver->subtype == PTY_TYPE_MASTER);
Reference: https://syzkaller.appspot.com/bug?id=2410d22f1d8e5984217329dd0884b01d99e3e48d

"The problem started with commit 7721383f4199 ("Bluetooth: hci_uart: Support
operational speed during setup") which introduced a new way for how
tty_set_termios() could end up being called for a master pty."

Fix it by by preventing setting the HCI line discipline for PTYs in
hci_uart_tty_open().

Reported-by: syzbot+a950165cbb86bdd023a4@...kaller.appspotmail.com
Cc: Johan Hovold <johan@...nel.org>
Cc: Marcel Holtmann <marcel@...tmann.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: Shuah Khan <shuah@...nel.org>
---
 drivers/bluetooth/hci_ldisc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index fbf7b4df23ab..c8faa4759cb7 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -475,9 +475,9 @@ static int hci_uart_tty_open(struct tty_struct *tty)
 	BT_DBG("tty %p", tty);
 
 	/* Error if the tty has no write op instead of leaving an exploitable
-	 * hole
+	 * hole. In addition check if setting HCI line discipline is allowed.
 	 */
-	if (tty->ops->write == NULL)
+	if (tty->ops->write == NULL || tty->ops->set_termios == NULL)
 		return -EOPNOTSUPP;
 
 	hu = kzalloc(sizeof(struct hci_uart), GFP_KERNEL);
-- 
2.17.1