netdev - Re: [PATCH net 2/4] rtl8150: Use heap buffers for all register access

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Date:   Tue, 7 Feb 2017 13:42:04 +0100
From:   'Greg KH' <greg@...ah.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     Petko Manolov <petkan@...leusys.com>,
        Ben Hutchings <ben@...adent.org.uk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH net 2/4] rtl8150: Use heap buffers for all register access

On Tue, Feb 07, 2017 at 11:56:51AM +0000, David Laight wrote:
> From: Greg KH
> > Sent: 07 February 2017 10:52
> > To: Petko Manolov
> > Cc: Ben Hutchings; David Laight; netdev@...r.kernel.org; linux-usb@...r.kernel.org
> > Subject: Re: [PATCH net 2/4] rtl8150: Use heap buffers for all register access
> > 
> > On Tue, Feb 07, 2017 at 12:34:52PM +0200, Petko Manolov wrote:
> > > On 17-02-06 16:25:20, Ben Hutchings wrote:
> > > > On Mon, Feb 06, 2017 at 04:09:18PM +0000, David Laight wrote:
> > > > > From: Ben Hutchings
> > > > [...]
> > > > > > +	ret = usb_control_msg(dev->udev, usb_rcvctrlpipe(dev->udev, 0),
> > > > > > +			      RTL8150_REQ_GET_REGS, RTL8150_REQT_READ,
> > > > > > +			      indx, 0, buf, size, 500);
> > > > > > +	if (ret > 0 && ret <= size)
> > > > > > +		memcpy(data, buf, ret);
> > > > >
> > > > > If ret > size something is horridly wrong.
> > > > > Silently not updating the callers buffer at all cannot be right.
> > > >
> > > > Yes, it seems strange to check this.  I originally wrote this as ret >
> > > > 0, but then I checked the usbnet core and found __usbnet_read_cmd()
> > > > has the second comparison as well.
> > > >
> > > > > > +	kfree(buf);
> > > > > > +	return ret;
> > >
> > > Since we return what usb_control_msg() told us to return i assume the error code
> > > will be available to anybody who cares.
> > >
> > > > > I can't help feeling that it would be better to add a wrapper to
> > > > > usb_control_msg() that does the kmalloc() and memcpy()s and
> > > > > drop that into all the call sites.
> > > >
> > > > It might be.  Right now I'm trying to patch up a bunch of regressions rather
> > > > than argue over an API change.
> > >
> > > Right, first thing first.
> > >
> > > I am in favor of changing the API, but this should not happen in the stable
> > > releases.  I hope Greg will make up his mind and let us know.
> > 
> > make up my mind about what?  These are bugs, they should be fixed, I'm
> > not taking a total api change at this point in time, sorry.
> 
> Adding a usb_control_msg_with_malloc() wrapper is a smaller change than those
> proposed. The smaller churn probably makes back porting other changes easier.
> 
> Given the nature of this problem, and how common it seems to be,
> it is almost worth renaming usb_control_msg() itself so that all the
> callers are properly audited.

As this is something that we have been auditing for a decade now, I
don't think you will find all that many instances :)

But for now, fixes like this are fine, if someone wants to tackle the
larger issue here, with a new api function, that would be great.

thanks,

greg k-h