Re: [PATCH] firmware: arm_scmi: avoid double free in error flow

[Wen Yang]

On 2019/11/26 12:13 äå, Sudeep Holla wrote:
> On Mon, Nov 25, 2019 at 11:54:09PM +0800, Wen Yang wrote:
> > If device_register() fails, both put_device() and kfree()
> > are called, ending with a double free of the scmi_dev.
>
> Correct.
>
> > Calling kfree() is needed only when a failure happens between the
> > allocation of the scmi_dev and its registration, so move it to
> > there and remove it from the error flow.
>
> kstrdup_const can fail and in that case device is not yet registered,
> so we need to free. Since device_register() calls put_device() on failure
> too, I would just drop it as it's unnecessary, not sure why I have added
> it in the first place. Can you re-spin the patch dropping put_device
> and renaming put_dev label to something like free_const.
>
> --
> Regards,
> Sudeep

Hi Sudeep,
Thanks for your comments.
Let's check the code like this:

int device_register(struct device *dev)
{
        device_initialize(dev);   --> Initialize kobj-> kref to 1
        return device_add(dev);
}

int device_add(struct device *dev)
{
...
        dev = get_device(dev);  --> kobj-> kref increases by 1
...
done:
        put_device(dev);  --> kobj-> kref decreases by 1 and is now 1
        return error;
...
}

So we also need to call put_device (),
and the original patch should be fine.
Please kindly help to check again, thank you.

--
Regards,
Wen