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

[Stepan Moskovchenko]

On 8/12/2014 9:12 AM, Kumar Gala wrote:
> On Aug 11, 2014, at 9:42 PM, Stepan Moskovchenko <stepanm@xxxxxxxxxxxxxx> wrote:
>
> > When we parse the device tree and allocate platform
> > devices, the 'name' of the newly-created platform_device
> > is set to point to the 'name' field of the 'struct device'
> > embedded within the platform_device. This is dangerous,
> > because the name of the 'struct device' is dynamically
> > allocated. Drivers may call dev_set_name() on the device,
> > which will free and reallocate the name of the device,
> > leaving the 'name' of the platform_device pointing to the
> > now-freed memory.
> >
> > Furthermore, if the dev_set_name() call is made from a
> > driver's probe() function and a subsequent request results
> > in probe deferral, the dangling 'name' reference may lead
> > to the device being re-probed using the wrong driver.
> >
> > To mitigate these scenarios, we use kstrdup to perform a
> > deep copy of the device name when assigning the name of the
> > platform_device, so that the platform_device name is
> > unaffected by any calls to dev_set_name() that might made
> > by drivers to rename the embedded 'struct device'.
> >
> > Signed-off-by: Stepan Moskovchenko <stepanm@xxxxxxxxxxxxxx>
> > ---
> > I suppose creating a 'pdev_set_name' API may seem like
> > another possibility, but I feel that dev.name and pdev.name
> > have two different meanings. One is used for device/driver
> > binding purposes, whereas the other serves a more general
> > identification purpose, and is used for things like sysfs.
> > Drivers might want to change dev.name while leaving the
> > pdev.name alone. I guess yet another possibility would be
> > to prohibit calling dev_set_name() on devices created from
> > device tree, but a driver does not necessarily know how a
> > given platform_device was allocated.
> >
> > drivers/of/device.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/device.c b/drivers/of/device.c
> > index f685e55..fe5f025 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
>
> Don’t we need to free this is of_device_unregister() now?
>
> - k

Argh. I was confused by the asymmetric naming of the APIs, but after 
digging through the callers outside from drivers/of/, it looks like 
things do eventually filter down to of_device_add() in all the cases I 
could find. So yes, this does need to be fixed. Expect v2 soon.

Thanks
Steve

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