[PATCH v2] Bluetooth: hci_ldisc: check for missing tty operations

[Vladis Dronov <vdronov@redhat.com>]

Certain ttys operations (pty_unix98_ops) lack tiocmget() and tiocmset()
functions which are called by the certain HCI UART protocols (hci_ath,
hci_bcm, hci_intel, hci_mrvl, hci_qca) via hci_uart_set_flow_control()
or directly. This leads to an execution at NULL and can be triggered by
an unprivileged user. Fix this by adding a check for the missing tty
operations the same way it is done for write().

This fixes CVE-2019-10207. The Fixes: lines list commits where calls to
tiocm[gs]et() or hci_uart_set_flow_control() were added to the HCI UART
protocols.

Link: https://syzkaller.appspot.com/bug?id=1b42faa2848963564a5b1b7f8c837ea7b55ffa50
Reported-by: syzbot+79337b501d6aa974d0f6@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org # v2.6.36+
Fixes: c19483cc5e56 ("bluetooth: Fix missing NULL check")
Fixes: b3190df62861 ("Bluetooth: Support for Atheros AR300x serial chip")
Fixes: 118612fb9165 ("Bluetooth: hci_bcm: Add suspend/resume PM functions")
Fixes: ff2895592f0f ("Bluetooth: hci_intel: Add Intel baudrate configuration support")
Fixes: 162f812f23ba ("Bluetooth: hci_uart: Add Marvell support")
Fixes: fa9ad876b8e0 ("Bluetooth: hci_qca: Add support for Qualcomm Bluetooth chip wcn3990")
Signed-off-by: Vladis Dronov <vdronov@redhat.com>
---

out-of-commit-message-note:

I believe, this is a good location for the check. This way we protect protocols
which does not call tiocm[gs]et() or hci_uart_set_flow_control() but may
change to call them in the future.

Also we do not need hci_uart_has_tiocm_support() helper now.

 drivers/bluetooth/hci_ldisc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/bluetooth/hci_ldisc.c b/drivers/bluetooth/hci_ldisc.c
index c84f985f348d..4a85c51d0307 100644
--- a/drivers/bluetooth/hci_ldisc.c
+++ b/drivers/bluetooth/hci_ldisc.c
@@ -459,10 +459,11 @@ 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
+	/* Error if the tty has no write or tiocm[gs]et ops instead of leaving
+	 * an exploitable hole
 	 */
-	if (tty->ops->write == NULL)
+	if (tty->ops->write == NULL || tty->ops->tiocmget == NULL ||
+	    tty->ops->tiocmset == NULL)
 		return -EOPNOTSUPP;
 
 	hu = kzalloc(sizeof(struct hci_uart), GFP_KERNEL);
-- 
2.21.0