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Subject[PATCH v2] tty: Fix WARNING in tty_set_termios()
Date
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 the problem by preventing setting the HCI line discipline for PTYs
from hci_uart_setup() and hci_uart_set_flow_control().

The reproducer is used to reproduce the problem and verify the fix.

Reported-by: syzbot+a950165cbb86bdd023a4@syzkaller.appspotmail.com
Signed-off-by: Shuah Khan <shuah@kernel.org>
---
drivers/bluetooth/hci_ldisc.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index fbf7b4df23ab..ce84ca91ca70 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -314,6 +314,11 @@ void hci_uart_set_flow_control(struct hci_uart *hu, bool enable)
return;
}

+ /* don't set HCI line discipline on PTYs */
+ if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+ tty->driver->subtype == PTY_TYPE_MASTER)
+ return;
+
if (enable) {
/* Disable hardware flow control */
ktermios = tty->termios;
@@ -384,11 +389,17 @@ void hci_uart_set_baudrate(struct hci_uart *hu, unsigned int speed)
static int hci_uart_setup(struct hci_dev *hdev)
{
struct hci_uart *hu = hci_get_drvdata(hdev);
+ struct tty_struct *tty = hu->tty;
struct hci_rp_read_local_version *ver;
struct sk_buff *skb;
unsigned int speed;
int err;

+ /* don't set HCI line discipline on PTYs */
+ if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
+ tty->driver->subtype == PTY_TYPE_MASTER)
+ return -EINVAL;
+
/* Init speed if any */
if (hu->init_speed)
speed = hu->init_speed;
--
2.17.1
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