Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for drivers

[Greg KH <greg@kroah.com>]

On Fri, Oct 20, 2017 at 01:54:36PM +0000, Mario.Limonciello@dell.com wrote:
> > -----Original Message-----
> > From: Greg KH [mailto:greg@kroah.com]
> > Sent: Friday, October 20, 2017 8:22 AM
> > To: Limonciello, Mario <Mario_Limonciello@Dell.com>
> > Cc: dvhart@infradead.org; Andy Shevchenko <andy.shevchenko@gmail.com>;
> > LKML <linux-kernel@vger.kernel.org>; platform-driver-x86@vger.kernel.org; Andy
> > Lutomirski <luto@kernel.org>; quasisec@google.com; pali.rohar@gmail.com;
> > rjw@rjwysocki.net; mjg59@google.com; hch@lst.de; Alan Cox
> > <gnomes@lxorguk.ukuu.org.uk>
> > Subject: Re: [PATCH v10 13/15] platform/x86: wmi: create userspace interface for
> > drivers
> > 
> > On Thu, Oct 19, 2017 at 12:50:16PM -0500, Mario Limonciello wrote:
> > > +	wblock = container_of(wdev, struct wmi_block, dev);
> > > +	if (!wblock)
> > > +		return -ENODEV;
> > 
> > How can container_of() ever return NULL?  If so, you have a very odd
> > memory layout...
> > 
> 
> I'm assuming this is from set_required_buffer_size right?
> 
> The symbol is exported out for other drivers to use.  It's possible for another
> driver to allocate a wmi_device structure that's not part of a wblock.

Fine, but your test does not do anything at all.

> > > +	list_for_each_entry_safe(wblock, next, &wmi_block_list, list) {
> > > +		wdriver = container_of(wblock->dev.dev.driver,
> > > +					struct wmi_driver, driver);
> > > +		if (!wdriver)
> > > +			continue;
> > 
> > Same here.  And other places in this file.
> > 
> 
> This one it's possible that a driver isn't bound to a device, and when
> that happens wdriver is NULL.

Again, that's not what you are testing at all.

container_of() is just pointer math.  If you pass in NULL, you will get
a non-NULL value (incremented or decremented).  If you pass in a very
tiny number, you might get NULL, but that's still really wrong.

In other words, these tests will _NEVER_ fail.  Go ahead, try it :)

thanks,

greg k-h