linux-kernel - Re: [PATCH v2 2/4] of: dynamic: add of_property_alloc() and of_property

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Date:   Thu, 2 Jun 2022 08:58:28 +0200
From:   Clément Léger <clement.leger@...tlin.com>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Nathan Lynch <nathanl@...ux.ibm.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Daniel Henrique Barboza <danielhb413@...il.com>,
        David Gibson <david@...son.dropbear.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Ohhoon Kwon <ohoono.kwon@...sung.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        YueHaibing <yuehaibing@...wei.com>, devicetree@...r.kernel.org,
        Steen Hegelund <steen.hegelund@...rochip.com>,
        linux-kernel@...r.kernel.org, Lizhi Hou <lizhi.hou@...inx.com>,
        Allan Nielsen <allan.nielsen@...rochip.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Horatiu Vultur <horatiu.vultur@...rochip.com>
Subject: Re: [PATCH v2 2/4] of: dynamic: add of_property_alloc() and
 of_property_free()

Le Wed, 1 Jun 2022 15:32:29 -0700,
Tyrel Datwyler <tyreld@...ux.ibm.com> a écrit :

> >  /**
> > - * __of_prop_dup - Copy a property dynamically.
> > - * @prop:	Property to copy
> > + * of_property_free - Free a property allocated dynamically.
> > + * @prop:	Property to be freed
> > + */
> > +void of_property_free(const struct property *prop)
> > +{
> > +	if (!of_property_check_flag(prop, OF_DYNAMIC))
> > +		return;
> > +  
> 
> This looks wrong to me. From what I understand the value data is allocated as
> trailing memory that is part of the property allocation itself. (ie. prop =
> kzalloc(sizeof(*prop) + len, allocflags)). So, kfree(prop) should also take care
> of the trailing value data. Calling kfree(prop->value) is bogus since
> prop->value wasn't dynamically allocated on its own.

kfree(prop->value) is only called if the value is not the trailing data
of the property so I don't see what is wrong there. In that case, only
kfree(prop) is called.

> 
> Also, this condition will always fail. You explicitly set prop->value = prop + 1
> in alloc.

The user that did allocated the property might want to provide its own
"value". In that case, prop->value would be overwritten by the user
allocated value and thus the check would be true, hence calling
kfree(prop->value).

> 
> Maybe I need to go back and look at v1 again.
> 
> -Tyrel
> 
> > +	if (prop->value != prop + 1)
> > +		kfree(prop->value);
> > +
> > +	kfree(prop->name);
> > +	kfree(prop);
> > +}
> > +EXPORT_SYMBOL(of_property_free);
> > +


-- 
Clément Léger,
Embedded Linux and Kernel engineer at Bootlin
https://bootlin.com