linux-kernel - Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

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Message-Id: <201512251402.42066@pali>
Date:	Fri, 25 Dec 2015 14:02:41 +0100
From:	Pali Rohár <pali.rohar@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	Darren Hart <dvhart@...radead.org>,
	Gabriele Mazzotta <gabriele.mzt@...il.com>,
	Michał Kępień <kernel@...pniu.pl>,
	Andy Lutomirski <luto@...nel.org>,
	platform-driver-x86@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

On Friday 25 December 2015 02:23:04 Andy Lutomirski wrote:
> On Thu, Dec 24, 2015 at 1:18 PM, Pali Rohár <pali.rohar@...il.com>
> wrote:
> > According to Dell WMI document mentioned in ML dicussion archived
> > at http://www.spinics.net/lists/platform-driver-x86/msg07220.html
> > OS should check Dell WMI descriptor structure. Structure also
> > provide Dell WMI interface version which is used later.
> 
> I will rebase my big series on top of this.  It'll give me a good
> excuse to test that I got the probe ordering right.  (The code is
> explicitly intended to support use cases like this, and now I'll have
> a real-world test for it.)  I'll also test this in a bit.

Ok!

> > +MODULE_ALIAS("wmi:"DELL_DESCRIPTOR_GUID);
> 
> I don't think this is necessary.  The driver will only work if both
> wmi devices and, hence, modaliases are present, so there's no need to
> cause just one or the other to trigger dell-wmi autoloading.

Maybe now when you are working on big WMI patch series is time to change 
modalias support in WMI to support AND-conjunction (&&) on WMI aliases, 
not just OR (one alias match).

Something like: load dell-wmi.ko driver if system provides both WMI 
GUIDs.

> > +/**
> 
> > + * Descriptor buffer is 128 byte long and contains:
> This isn't kerneldoc format, so I think this should just be "/*".
> 

Ok, I will fix this in next version.

> > +       if (obj->buffer.length != 128) {
> > +               pr_err("Dell descriptor buffer has invalid length
> > (%d)\n", +                       obj->buffer.length);
> > +               kfree(obj);
> > +               return -EINVAL;
> > +       }
> 
> I would advocate for being more permissive: a buffer that is actually
> too short for the fields we need would result in -EINVAL, but a
> buffer that isn't 128 bytes would just be a warning and not cause
> module load to fail.
> 
> --Andy

Sounds good, I will change this part.

-- 
Pali Rohár
pali.rohar@...il.com

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