Re: [PATCH v2] drm: bridge: cdns-mhdp8546: Fix possible null pointer dereference

[Robert Foss]

Hey Aleksandr,

On Fri, Apr 12, 2024 at 10:40 AM Aleksandr Mishin <amishin@xxxxxxxxxx> wrote:
>
> In cdns_mhdp_atomic_enable(), the return value of drm_mode_duplicate() is
> assigned to mhdp_state->current_mode, and there is a dereference of it in
> drm_mode_set_name(), which will lead to a NULL pointer dereference on
> failure of drm_mode_duplicate().
>
> Fix this bug by adding a check of mhdp_state->current_mode.
>
> Fixes: fb43aa0acdfd ("drm: bridge: Add support for Cadence MHDP8546 DPI/DP bridge")
> Signed-off-by: Aleksandr Mishin <amishin@xxxxxxxxxx>
> ---
> v2: Fix a mistake where the mutex remained locked
>
>  drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> index e226acc5c15e..5b831d6d7764 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> @@ -2059,6 +2059,11 @@ static void cdns_mhdp_atomic_enable(struct drm_bridge *bridge,
>         mhdp_state = to_cdns_mhdp_bridge_state(new_state);
>
>         mhdp_state->current_mode = drm_mode_duplicate(bridge->dev, mode);
> +       if (!mhdp_state->current_mode) {
> +               ret = -EINVAL;
> +               goto out;
> +       }
> +

This chunk no longer applies on drm-misc-next.

I think the approach here is still better than what is in
drm-misc-next since it unlocks link_mutex.

Can you rebase + reword the commit message and send that out as v3?

>         drm_mode_set_name(mhdp_state->current_mode);
>
>         dev_dbg(mhdp->dev, "%s: Enabling mode %s\n", __func__, mode->name);
> --
> 2.30.2
>