Re: [PATCH v4] bluetooth: Fix WARNING in tty_set_termios()

[shuah]

On 2/3/19 10:39 PM, Marcel Holtmann wrote:

Hi Shuah,


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+a950165cbb86bdd02...@syzkaller.appspotmail.com
Cc: Johan Hovold 
Cc: Marcel Holtmann 
Cc: Al Viro 
Signed-off-by: Shuah Khan 
---
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.
 */


this comment is wrong. The result of setting the HCI line discipline is a call into 
hci_uart_tty_open. You have to check ops->write and ops->set_termios since both 
are required. That is it.


I will fix the comment.




-   if (tty->ops->write == NULL)
+   if (tty->ops->write == NULL || tty->ops->set_termios == NULL)
return -EOPNOTSUPP;


And while at it, change this to (!tty->ops->write).



Okay. I will fix both.

thanks,
-- Shuah

Re: [PATCH v4] bluetooth: Fix WARNING in tty_set_termios()

[Marcel Holtmann]

Hi Shuah,

> 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+a950165cbb86bdd02...@syzkaller.appspotmail.com
> Cc: Johan Hovold 
> Cc: Marcel Holtmann 
> Cc: Al Viro 
> Signed-off-by: Shuah Khan 
> ---
> 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.
>*/

this comment is wrong. The result of setting the HCI line discipline is a call 
into hci_uart_tty_open. You have to check ops->write and ops->set_termios since 
both are required. That is it.

> - if (tty->ops->write == NULL)
> + if (tty->ops->write == NULL || tty->ops->set_termios == NULL)
>   return -EOPNOTSUPP;

And while at it, change this to (!tty->ops->write).

Regards

Marcel