[PATCH v3 1/3] drm: adv7511: Fix use-after-free in adv7533_attach_dsi()

[Geert Uytterhoeven]

Hi Biju,

On Wed, Nov 6, 2024 at 7:49 PM Biju Das <biju.das.jz at bp.renesas.com> wrote:
> The host_node pointer assigned and freed in adv7533_parse_dt()
> and later adv7533_attach_dsi() uses the same. Fix this issue
> by freeing the host_node in adv7533_attach_dsi() instead of
> adv7533_parse_dt().
>
> Fixes: 1e4d58cd7f88 ("drm/bridge: adv7533: Create a MIPI DSI device")
> Cc: stable at vger.kernel.org
> Signed-off-by: Biju Das <biju.das.jz at bp.renesas.com>
> ---
> Changes in v3:
>  - Replace __free construct with readable of_node_put().
> Changes in v2:
>  - Added the tag "Cc: stable at vger.kernel.org" in the sign-off area.
>  - Dropped Archit Taneja invalid Mail address

Thanks for the update!

> --- a/drivers/gpu/drm/bridge/adv7511/adv7533.c
> +++ b/drivers/gpu/drm/bridge/adv7511/adv7533.c
> @@ -143,6 +143,7 @@ int adv7533_attach_dsi(struct adv7511 *adv)
>                                                  };
>
>         host = of_find_mipi_dsi_host_by_node(adv->host_node);
> +       of_node_put(adv->host_node);

This still looks fragile to me, as afterwards a pointer to a freed
node is left in struct adv7511.host_node. It would be safer to also
clear adv->host_node here.

However, taking a look from a distance, the code looks like:

    static int adv7511_probe(struct i2c_client *i2c)
    {
            ...
            adv7533_parse_dt(dev->of_node, adv7511);
            ...
            if (adv7511->info->has_dsi)
                    ret = adv7533_attach_dsi(adv7511);
            ...
    }

The only reason adv7511.host_node exists is to pass it from
adv7533_parse_dt() to adv7533_attach_dsi().
So what about making this explicit?
  1. Let adv7533_parse_dt() return the host_node or an error pointer,
  2. Pass the host_node as a parameter to adv7533_attach_dsi(),
  3. Call of_node_put() in adv7511_probe() after use.

>         if (!host)
>                 return dev_err_probe(dev, -EPROBE_DEFER,
>                                      "failed to find dsi host\n");
> @@ -181,8 +182,6 @@ int adv7533_parse_dt(struct device_node *np, struct adv7511 *adv)
>         if (!adv->host_node)
>                 return -ENODEV;
>
> -       of_node_put(adv->host_node);
> -
>         adv->use_timing_gen = !of_property_read_bool(np,
>                                                 "adi,disable-timing-generator");

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-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