linux-kernel - Re: [PATCH v2] powerpc/mpc5xxx: Avoid dereferencing potentially freed memory

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Message-ID: <1444988979.12954.1.camel@ellerman.id.au>
Date:	Fri, 16 Oct 2015 20:49:39 +1100
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:	benh@...nel.crashing.org, paulus@...ba.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH v2] powerpc/mpc5xxx: Avoid dereferencing potentially
 freed memory

On Fri, 2015-10-16 at 08:20 +0200, Christophe JAILLET wrote:
> Le 15/10/2015 08:36, Michael Ellerman a écrit :
> > On Thu, 2015-10-15 at 07:56 +0200, Christophe JAILLET wrote:
> > > Use 'of_property_read_u32()' instead of
> > > 'of_get_property()'+pointer
> > > dereference in order to avoid access to potentially freed memory.
> > > 
> > > Use 'of_get_next_parent()' to simplify the while() loop and avoid
> > > the
> > > need of a temp variable.
> > > 
> > > Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> > > ---
> > > v2: Use of_property_read_u32 instead of of_get_property+pointer
> > > dereference
> > > *** Untested ***
> > Thanks.
> > 
> > Can someone with an mpc5xxx test this?
> 
> Hi,
> I don't think it is an issue, but while looking at another similar 
> patch, I noticed that the proposed patch adds a call to
> be32_to_cpup() 
> (within of_property_read_u32).
> Apparently, powerPC is a BE architecture, so this call should be a no
> -op.
> 
> Just wanted to point it out, in case of.

Hi Christoph,

I'm not sure I follow.

The device tree is always big endian, but of_property_read_u32() does
the
conversion to CPU endian for you already. That is one of the advantages
of
using it.

cheers

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