linux-kernel - Re: [PATCH] of: Deep-copy names of platform devices

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Date:	Fri, 15 Aug 2014 11:52:50 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	Stephen Boyd <sboyd@...eaurora.org>,
	Stepan Moskovchenko <stepanm@...eaurora.org>
Cc:	Rob Herring <robh+dt@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH] of: Deep-copy names of platform devices

On Fri, Aug 15, 2014 at 11:45 AM, Grant Likely <grant.likely@...aro.org> wrote:
> On Tue, 12 Aug 2014 18:46:36 -0700, Stephen Boyd <sboyd@...eaurora.org> wrote:
>> On 08/12/14 17:57, Stepan Moskovchenko wrote:
>> > diff --git a/drivers/of/device.c b/drivers/of/device.c
>> > index f685e55..3e116f6 100644
>> > --- a/drivers/of/device.c
>> > +++ b/drivers/of/device.c
>> > @@ -54,7 +54,7 @@ int of_device_add(struct platform_device *ofdev)
>> >
>> >     /* name and id have to be set so that the platform bus doesn't get
>> >      * confused on matching */
>> > -   ofdev->name = dev_name(&ofdev->dev);
>> > +   ofdev->name = kstrdup(dev_name(&ofdev->dev), GFP_KERNEL);
>> >     ofdev->id = -1;
>> >
>> >     /* device_add will assume that this device is on the same node as
>> > @@ -76,6 +76,7 @@ EXPORT_SYMBOL(of_device_register);
>> >  void of_device_unregister(struct platform_device *ofdev)
>> >  {
>> >     device_unregister(&ofdev->dev);
>> > +   kfree(ofdev->name);
>>
>> This probably ought to be swapped because we don't know if ofdev isn't
>> pointing to freed memory after device_unregister().
>
> Actually, the only safe place to free the memory is inside the
> platform_device release function. platform_device_release() in
> drivers/base/platform.c. Unfortunately there isn't a good way from that
> function to figure out if the name has been allocated the 'OF' way.
>
> It is not safe to free it here because there could still be references
> to the platform_device after device_unregister exits.

We could fix the problem by making platform_device_alloc() also do a
kstrdup() when assigning the name. Then the release function can
unconditionally free the name field. Care to try that out?

g.
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