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

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Date:   Wed, 25 Jul 2018 10:57:01 -0300
From:   Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
To:     Akihiro TSUKADA <tskd08@...il.com>
Cc:     Colin Ian King <colin.king@...onical.com>,
        linux-media@...r.kernel.org, Antti Palosaari <crope@....fi>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        mika.batsman@...il.com
Subject: Re: media: dvb-usb-v2/gl861: ensure USB message buffers DMA'able

Em Tue, 3 Jul 2018 21:07:07 +0900
Akihiro TSUKADA <tskd08@...il.com> escreveu:

> 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.

There was another patch proposed to fix this issue with does the
right thing when rlen == 0. I rebased it on the top of the current
tree:
	https://git.linuxtv.org/media_tree.git/commit/?id=0b666e1c8120c0b17a8a68aaed58e22011f06ab3

That should cover both cases.

Thanks,
Mauro