linux-kernel - Re: [PATCH v4 OPT2] driver core: Fix use-after-free and double free on glue directory

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Message-ID: <319ae04497cf1982076bf801cfdf565046096fd4.camel@kernel.crashing.org>
Date:   Thu, 04 Jul 2019 08:57:13 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Muchun Song <smuchun@...il.com>
Cc:     rafael@...nel.org, prsood@...eaurora.org, mojha@...eaurora.org,
        gkohli@...eaurora.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 OPT2] driver core: Fix use-after-free and double free
 on glue directory

On Wed, 2019-07-03 at 21:36 +0200, Greg KH wrote:
> 
> > -static struct kobject *get_device_parent(struct device *dev,
> > -					 struct device *parent)
> > +/**
> > + * __get_device_parent() - Get the parent device kobject.
> > + * @dev: Pointer to the device structure.
> > + * @parent: Pointer to the parent device structure.
> > + * @lock: When we live in a glue directory, should we hold the
> > + *        gdp_mutex lock when this function returns? If @lock
> > + *        is true, this function returns with the gdp_mutex
> > + *        holed. Otherwise it will not.
> 
> Ugh, if you are trying to get me to hate one version of these patches,
> this is how you do it :)
> 
> A function should not "sometimes takes a lock, sometimes does not,
> depending on a parameter passed into it"  That way lies madness...

Yes, I prefer this approach to the fix but I dont like the patch either
for the same reason...

 ...

> Anyway, this is a mess.
> 
> Ugh I hate glue dirs...

Amen...

Ben.