linux-kernel - Re: [PATCH] reset: Fix potential use-after-free in __of_reset_control

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Date:   Mon, 8 Oct 2018 15:12:02 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Philipp Zabel <p.zabel@...gutronix.de>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH] reset: Fix potential use-after-free in __of_reset_control_get()

Hi Philipp,

On Mon, Oct 8, 2018 at 2:56 PM Philipp Zabel <p.zabel@...gutronix.de> wrote:
> On Mon, 2018-10-08 at 13:14 +0200, Geert Uytterhoeven wrote:
> > Calling of_node_put() decreases the reference count of a device tree
> > object, and may free some data.
> >
> > However, the of_phandle_args structure embedding it is passed to
> > reset_controller_dev.of_xlate() after that, so it may still be accessed.
> >
> > Move the call to of_node_put() down to fix this.
> >
> > Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> > ---
> >  drivers/reset/core.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/reset/core.c b/drivers/reset/core.c
> > index 225e34c56b94a2e3..bc9df10d31b4bae1 100644
> > --- a/drivers/reset/core.c
> > +++ b/drivers/reset/core.c
> > @@ -496,27 +496,28 @@ struct reset_control *__of_reset_control_get(struct device_node *node,
> >                       break;
> >               }
> >       }
> > -     of_node_put(args.np);
> >
> >       if (!rcdev) {
> > -             mutex_unlock(&reset_list_mutex);
> > -             return ERR_PTR(-EPROBE_DEFER);
> > +             rstc = ERR_PTR(-EPROBE_DEFER);
> > +             goto out;
> >       }
> >
> >       if (WARN_ON(args.args_count != rcdev->of_reset_n_cells)) {
> > -             mutex_unlock(&reset_list_mutex);
> > -             return ERR_PTR(-EINVAL);
> > +             rstc = ERR_PTR(-EINVAL);
> > +             goto out;
> >       }
> >
> >       rstc_id = rcdev->of_xlate(rcdev, &args);
> >       if (rstc_id < 0) {
> > -             mutex_unlock(&reset_list_mutex);
> > -             return ERR_PTR(rstc_id);
> > +             rstc = ERR_PTR(rstc_id);
> > +             goto out;
> >       }
> >
> >       /* reset_list_mutex also protects the rcdev's reset_control list */
> >       rstc = __reset_control_get_internal(rcdev, rstc_id, shared);
> >
> > +out:
> > +     of_node_put(args.np);
> >       mutex_unlock(&reset_list_mutex);
>
> Thank you for the patch. I'd like to move of_node_put after mutex_unlock
> for symmetry. If you agree, I can switch the two when applying.

No objection, thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds