linux-kernel - Re: [PATCH] kernel/resource: Invalid memory access in __release

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Message-ID: <CAPybu_0oOtnHPAJfQM2iX5JrHy58LawNX-qhUHm8r83ZD1t+1Q@mail.gmail.com>
Date:	Mon, 20 Apr 2015 22:24:25 +0200
From:	Ricardo Ribalda Delgado <ricardo.ribalda@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Vinod Koul <vinod.koul@...el.com>, Cliff Wickman <cpw@....com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Jakub Sitnicki <jsitnicki@...il.com>,
	Thierry Reding <treding@...dia.com>,
	Mike Travis <travis@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>
Subject: Re: [PATCH] kernel/resource: Invalid memory access in __release_resource

Hi Bjorn!

Thanks for your promtly response.

On Mon, Apr 20, 2015 at 9:28 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> [+cc Grant (author of ac80a51e2ce5)]
>
> Hi Ricardo,
>
> On Mon, Apr 20, 2015 at 06:22:52PM +0200, Ricardo Ribalda Delgado wrote:
>>
>> If of_platform_depopulate is called later, resource->parent is
>> accessed (Offset 0x30 of address 0), causing a kernel error.
>
> Interesting; how'd you find this?  It looks like the
> of_platform_depopulate() code has been this way for a long time, so we
> must be doing something new that makes us trip over this now.  More
> analysis below...

I have an out of tree driver that dynamically adds devices to the device tree.

It was developed before the dynamic_of and dt_overlays existed. Now I
am porting my code to the new interfaces available. I am trying to do
it small steps.

First step was being able to depopulate a previously loaded device
tree. Old, code was calling of_platform_populate, so calling
of_platform_depopulate looked like the right choice. Unfortunately
everything crashed, and it turned out that this was the issue.

On my defense I would say, that the plan is to make this driver
public, once the hardware is stabilized and sold to the public.

>> @@ -237,6 +237,9 @@ static int __release_resource(struct resource *old)
>>  {
>>       struct resource *tmp, **p;
>>
>> +     if (!old->parent)
>> +             return -EINVAL;
>
> This path has been fine for a long time without testing for a NULL
> pointer, so I suspect this change papers over an issue that would be
> better fixed elsewhere.
>

This code is pretty tested, but dynamic remove is not.

> From reading drivers/base/platform.c, it looks like the intent is
> that platform device users would use these interfaces:

I can take a look to modify OF to use insert_resource(), but I still
think that no matter what, we should add this extra check, like the
propossed patch or maybe with a BUG_ON()....

Lets see what Grant thinks about this.

Thanks again!

-- 
Ricardo Ribalda
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