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

[Christophe JAILLET]

Le 16/10/2015 11:49, Michael Ellerman a Ãcrit :
> On Fri, 2015-10-16 at 08:20 +0200, Christophe JAILLET wrote:
> > Le 15/10/2015 08:36, Michael Ellerman a Ãcrit :
> > > 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@xxxxxxxxxx>
> > > > ---
> > > > 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

Hi,
sorry if un-clear.

What I mean is that in the patch related 
'powerpc/sysdev/mpc5xxx_clocks.c', there was no call to 'be32_to_cpup'.
So in the proposed patch, 'of_property_read_u32' adds it.

While in the patch against 'powerpc/kernel/prom.c', 'be32_to_cpup' was 
called explicitly.
So using 'of_property_read_u32' keep the same logic.


Basically the code from 'mpc5xxx_clocks.c' and from 'prom.c' were 
written the same way. I found spurious that a call to 'be32_to_cpup' was 
done in only one case.
Maybe, it was a missing in 'mpc5xxx_clocks.c'.


I don't know if it can be an issue or not. I just find it 'strange'.


CJ


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