Re: media: dvb-usb-v2/gl861: ensure USB message buffers DMA'able

[Akihiro TSUKADA]

Hi,
thanks for the report.

>  47        buf = NULL;
> 
> Condition rlen > 0, taking false branch.
> 
>  48        if (rlen > 0) {
>  49                buf = kmalloc(rlen, GFP_KERNEL);
>  50                if (!buf)
>  51                        return -ENOMEM;
>  52        }
> 
>  53        usleep_range(1000, 2000); /* avoid I2C errors */
>  54
>    CID 1470241 (#1 of 1): Explicit null dereferenced (FORWARD_NULL).
> var_deref_model: Passing null pointer buf to usb_control_msg, which
> dereferences it.
> 
>  55        ret = usb_control_msg(d->udev, usb_rcvctrlpipe(d->udev, 0),
> req, type,
>  56                              value, index, buf, rlen, 2000);
> 
> 
> The assignment of buf = NULL means a null buffer is passed down the usb
> control message stack until it eventually gets dereferenced. This only
> occurs when rlen <= 0.   I was unsure how to fix this for the case when
> rlen <= 0, so I am flagging this up as an issue that needs fixing.
> 

Since rlen is an u16, null pointer is passed only when rlen == 0,
so I think it is not a problem,
but I am OK to add a guard in order to make scan result clean.

regards,
Akihiro