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

[Laurent Pinchart]

On Wed, Nov 06, 2024 at 08:04:16PM +0100, Geert Uytterhoeven wrote:
> 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.

Or, alternatively, if keeping the node pointer in the adv7511 structure
is preferred, call of_node_put() at .remove() time.

> >         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");

-- 
Regards,

Laurent Pinchart