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References: <20190531011424.GA4374@zhanggen-UX430UQ> <eb8e2d33-e8f7-93a5-c8bc-98731c0d63b6@suse.cz> <20190605160043.GA4351@zhanggen-UX430UQ>
To:     Gen Zhang <blackgod016574@gmail.com>, Jiri Slaby <jslaby@suse.cz>
From:   Stephen Boyd <sboyd@kernel.org>
Subject: Re: [PATCH] clk: fix a missing-free bug in clk_cpy_name()
Cc:     mturquette@baylibre.com, linux-clk@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Date:   Thu, 06 Jun 2019 13:16:45 -0700
Message-Id: <20190606201646.B4CC4206BB@mail.kernel.org>
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Quoting Gen Zhang (2019-06-05 09:00:43)
> On Wed, Jun 05, 2019 at 08:38:00AM +0200, Jiri Slaby wrote:
> > On 31. 05. 19, 3:14, Gen Zhang wrote:
> > > In clk_cpy_name(), '*dst_p'('parent->name'and 'parent->fw_name') and =

> > > 'dst' are allcoted by kstrdup_const(). According to doc: "Strings=20
> > > allocated by kstrdup_const should be freed by kfree_const". So=20
> > > 'parent->name', 'parent->fw_name' and 'dst' should be freed.
> > >=20
> > > Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
> > > ---
> > > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > > index aa51756..85c4d3f 100644
> > > --- a/drivers/clk/clk.c
> > > +++ b/drivers/clk/clk.c
> > > @@ -3435,6 +3435,7 @@ static int clk_cpy_name(const char **dst_p, con=
st char *src, bool must_exist)
> > >     if (!dst)
> > >             return -ENOMEM;
> > > =20
> > > +   kfree_const(dst);
> >=20
> > So you are now returning a freed pointer in dst_p?
> Thanks for your reply. I re-examined the code, and this kfree is=20
> incorrect and it should be deleted.
> >=20
> > >     return 0;
> > >  }
> > > =20
> > > @@ -3491,6 +3492,8 @@ static int clk_core_populate_parent_map(struct =
clk_core *core)
> > >                             kfree_const(parents[i].name);
> > >                             kfree_const(parents[i].fw_name);
> > >                     } while (--i >=3D 0);
> > > +                   kfree_const(parent->name);
> > > +                   kfree_const(parent->fw_name);
> >=20
> > Both of them were just freed in the loop above, no?
> for (i =3D 0, parent =3D parents; i < num_parents; i++, parent++)
> Is 'parent' the same as the one from the loop above?

Yes. Did it change somehow?

>=20
> Moreover, should 'parents[i].name' and 'parents[i].fw_name' be freed by
> kfree_const()?
>=20

Yes? They're allocated with kstrdup_const() in clk_cpy_name(), or
they're NULL by virtue of the kcalloc and then kfree_const() does
nothing.

I'm having a hard time following what this patch is trying to fix. It
looks unnecessary though so I'm going to drop it from the clk review
queue.