Re: [PATCH] Bluetooth: hci_uart: check for missing tty operations in protocol handlers

[Vladis Dronov]

Hello, Marcel,

> why is this one hidden behind CONFIG_PM? The general baud rate changes are
> independent of runtime power management support.

hci_bcm calls hci_uart_set_flow_control() only from functions hidden behind
#ifdef-CONFIG_PM (surely this can change in the future), and so without
CONFIG_PM set it cannot hit the bug (as of now). So I've hidden the check
for tiocm[gs]et() behind #ifdef-CONFIG_PM too.

If you tell me it is better to remove this #ifdef, I'll remove it.

> And I would introduce a bool hci_uart_has_tiocm_support(struct hci_uart *)
> helper.

Great, I will add it to the v2 fix. I guess a good place for it is hci_ldisc.c,
near hci_uart_set_flow_control(), isn't it?

Best regards,
Vladis Dronov | Red Hat, Inc. | The Core Kernel | Senior Software Engineer

----- Original Message -----
> From: "Marcel Holtmann" <marcel@xxxxxxxxxxxx>
> To: "Vladis Dronov" <vdronov@xxxxxxxxxx>
> Cc: "Johan Hedberg" <johan.hedberg@xxxxxxxxx>, linux-bluetooth@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, "Suraj
> Sumangala" <suraj@xxxxxxxxxxx>, "Frederic Danis" <frederic.danis@xxxxxxxxxxxxxxx>, "Loic Poulain"
> <loic.poulain@xxxxxxxxx>, "Balakrishna Godavarthi" <bgodavar@xxxxxxxxxxxxxx>, syzkaller@xxxxxxxxxxxxxxxx
> Sent: Thursday, July 25, 2019 2:59:42 PM
> Subject: Re: [PATCH] Bluetooth: hci_uart: check for missing tty operations in protocol handlers
> 
> Hi Vladis,
> 
> > 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 to the protocols which use them.
> > 
> > This fixes CVE-2019-10207.
> > 
> > Link:
> > https://syzkaller.appspot.com/bug?id=1b42faa2848963564a5b1b7f8c837ea7b55ffa50
> > Reported-by: syzbot+79337b501d6aa974d0f6@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Cc: stable@xxxxxxxxxxxxxxx # v2.6.36+
> > 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@xxxxxxxxxx>
> > ---
> > drivers/bluetooth/hci_ath.c   | 3 +++
> > drivers/bluetooth/hci_bcm.c   | 5 +++++
> > drivers/bluetooth/hci_intel.c | 3 +++
> > drivers/bluetooth/hci_mrvl.c  | 3 +++
> > drivers/bluetooth/hci_qca.c   | 4 ++++
> > 5 files changed, 18 insertions(+)
> > 
> > diff --git a/drivers/bluetooth/hci_ath.c b/drivers/bluetooth/hci_ath.c
> > index a55be205b91a..99df8a13e47e 100644
> > --- a/drivers/bluetooth/hci_ath.c
> > +++ b/drivers/bluetooth/hci_ath.c
> > @@ -98,6 +98,9 @@ static int ath_open(struct hci_uart *hu)
> > 
> > 	BT_DBG("hu %p", hu);
> > 
> > +	if (!hu->tty->driver->ops->tiocmget || !hu->tty->driver->ops->tiocmset)
> > +		return -ENOTSUPP;
> > +
> > 	ath = kzalloc(sizeof(*ath), GFP_KERNEL);
> > 	if (!ath)
> > 		return -ENOMEM;
> > diff --git a/drivers/bluetooth/hci_bcm.c b/drivers/bluetooth/hci_bcm.c
> > index 8905ad2edde7..8c3e09cc341c 100644
> > --- a/drivers/bluetooth/hci_bcm.c
> > +++ b/drivers/bluetooth/hci_bcm.c
> > @@ -406,6 +406,11 @@ static int bcm_open(struct hci_uart *hu)
> > 
> > 	bt_dev_dbg(hu->hdev, "hu %p", hu);
> > 
> > +#ifdef CONFIG_PM
> > +	if (!hu->tty->driver->ops->tiocmget || !hu->tty->driver->ops->tiocmset)
> > +		return -ENOTSUPP;
> > +#endif
> > +
> 
> why is this one hidden behind CONFIG_PM? The general baud rate changes are
> independent of runtime power management support.
> 
> And I would introduce a bool hci_uart_has_tiocm_support(struct hci_uart *)
> helper.
> 
> Regards
> 
> Marcel