linux-kernel - Re: KMSAN: uninit-value in smsc75xx

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Date:   Wed, 14 Aug 2019 12:16:04 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexander Potapenko <glider@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        steve.glendinning@...well.net,
        syzbot <syzbot+6966546b78d050bb0b5d@...kaller.appspotmail.com>,
        LKML <linux-kernel@...r.kernel.org>,
        USB list <linux-usb@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>
Subject: Re: KMSAN: uninit-value in smsc75xx_bind

Am Dienstag, den 13.08.2019, 17:08 +0200 schrieb Andrey Konovalov:
> On Tue, Aug 13, 2019 at 2:43 PM Oliver Neukum <oneukum@...e.com> wrote:
> > 
> > 
> > Hi,
> > 
> > this looks like a false positive to me.
> > The offending code is likely this:
> > 
> >         if (size) {
> >                 buf = kmalloc(size, GFP_KERNEL);
> >                 if (!buf)
> >                         goto out;
> >         }
> > 
> >         err = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
> >                               cmd, reqtype, value, index, buf, size,
> >                               USB_CTRL_GET_TIMEOUT);
> > 
> > which uses 'buf' uninitialized. But it is used for input.
> > What is happening here?
> 
> AFAICS, the uninitialized use of buf that KMSAN points out is in the
> "if (buf & PMT_CTL_DEV_RDY)"  statement in smsc75xx_wait_ready(). Does
> __smsc75xx_read_reg/usb_control_msg() always initialize buf? Can it
> just initialize the first few bytes for example?
> 

Hi,

you are unfortunately right and this is not the only driver vulnerable
in this way. I am going through them.

	Regards
		Oliver