Re: [patch] HID: hid-logitech-dj: add some range checks

Benjamin Tissoires
2013-03-05T14:47:48Z

Hi Dan,

On Tue, Mar 5, 2013 at 2:06 PM, Dan Carpenter <dan.carpenter@oracle.com> wrote:
> We can't trust dj_report->device_index because it comes from the
> user and hasn't been range checked. It is used as an offset into
> the djrcv_dev->paired_dj_devices[] array which has 7 elements.
> There is one range check already in logi_dj_recv_add_djhid_device()
> and I have copy and pasted that here.
>
> DJ_DEVICE_INDEX_MIN is 1.
> DJ_DEVICE_INDEX_MAX is 6.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
> This is a static checker fix and I'm not certain it's correct,
> please look it over carefully.
>
> I do not know this code well, so I don't know why a zero index is
> invalid.
>
> diff --git a/drivers/hid/hid-logitech-dj.c b/drivers/hid/hid-logitech-dj.c
> index 9500f2f..c01cd25 100644
> --- a/drivers/hid/hid-logitech-dj.c
> +++ b/drivers/hid/hid-logitech-dj.c
> @@ -701,6 +701,13 @@ static int logi_dj_raw_event(struct hid_device *hdev,
> * anything else with it.
> */
>
> + if ((dj_report->device_index < DJ_DEVICE_INDEX_MIN) ||
> + (dj_report->device_index > DJ_DEVICE_INDEX_MAX)) {
> + dev_err(&hdev->dev, "%s: invalid device index:%d\n", __func__,
> + dj_report->device_index);
> + return true;
> + }
> +

Sorry, but it's a NACK in its current form:
- device_index = 0 is the receiver. IIRC, the receiver sends the
different REPORT_TYPE_NOTIF_*. So I would say that this patch blocks
events from the receiver.
- the DJ protocol specifies that the device index is between 1 and 6
and that 0 means the receiver. So unless there is a problem in the USB
line from the receiver to the driver, device index will be between 1
and 6 for input events. This is only true as long as with stay with
real firmware from Logitech, not from events from uhid.

If you want to add a check, it need to be in logi_dj_recv_forward_report().
The current access to djrcv_dev->paired_dj_devices[] in
delayedwork_callback() has been removed in latest HID tree:
https://git.kernel.org/cgit/linux/kernel/git/jikos/hid.git/log/?h=for-3.10/logitech

Cheers,
Benjamin

> spin_lock_irqsave(&djrcv_dev->lock, flags);
> if (dj_report->report_id = REPORT_ID_DJ_SHORT) {
> switch (dj_report->report_type) {
> --
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