Re: [PATCH 1/5] Bluetooth: Add RFCOMM TTY write return error codes

Peter Hurley
2013-07-24T23:12:13Z

On 07/02/2013 11:31 AM, Dean Jenkins wrote:
> It appears that rfcomm_tty_write() does not check that the
> passed in TTY device_data is not NULL and also does not check
> that the RFCOMM DLC serial data link pointer is not NULL.
>
> A kernel crash was observed whilst SLIP was bound to /dev/rfcomm0
> but the /dev/rfcomm0 had subsequently disconnected. Unfortunately,
> SLIP attempted to write to the now non-existant RFCOMM TTY device
> which caused a NULL pointer dereference because the device_data
> no longer existed.
>
> Therefore, add NULL pointer checks for the dev and dlc pointers
> and output kernel error debug to show that NULL had been detected.

Dean,

Sorry, I didn't see these until just now.

> Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
> ---
> net/bluetooth/rfcomm/tty.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
> index b6e44ad..56d28d1 100644
> --- a/net/bluetooth/rfcomm/tty.c
> +++ b/net/bluetooth/rfcomm/tty.c
> @@ -761,12 +761,24 @@ static void rfcomm_tty_close(struct tty_struct *tty, struct file *filp)
> static int rfcomm_tty_write(struct tty_struct *tty, const unsigned char *buf, int count)
> {
> struct rfcomm_dev *dev = (struct rfcomm_dev *) tty->driver_data;
> - struct rfcomm_dlc *dlc = dev->dlc;
> + struct rfcomm_dlc *dlc;
> struct sk_buff *skb;
> int err = 0, sent = 0, size;
>
> BT_DBG("tty %p count %d", tty, count);
>
> + if (!dev) {
> + BT_ERR("RFCOMM TTY device data structure does not exist");
> + return -ENODEV;
> + }
> +
> + dlc = dev->dlc;
> +
> + if (!dlc) {
> + BT_ERR("RFCOMM serial data link does not exist");
> + return -ENOLINK;
> + }
> +

A number of bugs in rfcomm contributed to the crash you observed.
Several other reporters have also noted crashes stemming from
device disconnect. The rfcomm device must not disappear while a tty
is in-use.

Fixes for these are in-progress in a patch series by Gianluca Anzolin
on linux-bluetooth ML.

Also, for the future, kernel bluetooth patches go to:
Gustavo Padovan <gustavo@padovan.org>
with cc's to:
Johan Hedberg <johan.hedberg@gmail.com>
Marcel Holtmann <marcel@holtmann.org>
linux-bluetooth@vger.kernel.org

Regards,
Peter Hurley