linux-kernel - Re: [PATCH v1 1/5] drm/mediatek: mtk_drm_drv: Fix kobject put for mtk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAGXv+5HUJUL342uMA7wjmm8TsBUveVa0i8k+BfB2aZXd--AoKg@mail.gmail.com>
Date: Wed, 2 Apr 2025 18:14:36 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: chunkuang.hu@...nel.org, p.zabel@...gutronix.de, airlied@...il.com, 
	simona@...ll.ch, matthias.bgg@...il.com, nancy.lin@...iatek.com, 
	ck.hu@...iatek.com, djkurtz@...omium.org, littlecvr@...omium.org, 
	bibby.hsieh@...iatek.com, dri-devel@...ts.freedesktop.org, 
	linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v1 1/5] drm/mediatek: mtk_drm_drv: Fix kobject put for
 mtk_mutex device ptr

On Wed, Apr 2, 2025 at 4:36 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> This driver is taking a kobject for mtk_mutex only once per mmsys
> device for each drm-mediatek driver instance, differently from the
> behavior with other components, but it is decrementing the kobj's
> refcount in a loop and once per mmsys: this is not right and will
> result in a refcount_t underflow warning when mediatek-drm returns
> multiple probe deferrals in one boot (or when manually bound and
> unbound).
>
> Besides that, the refcount for mutex_dev was not decremented for
> error cases in mtk_drm_bind(), causing another refcount_t warning
> but this time for overflow, when the failure happens not during
> driver bind but during component bind.
>
> In order to fix one of the reasons why this is happening, remove
> the put_device(xx->mutex_dev) loop from the mtk_drm_kms_init()'s
> put_mutex_dev label (and drop the label) and add a single call to
> correctly free the single incremented refcount of mutex_dev to
> the mtk_drm_unbind() function to fix the refcount_t underflow.
>
> Moreover, add the same call to the error cases in mtk_drm_bind()
> to fix the refcount_t overflow.
>
> Fixes: 1ef7ed48356c ("drm/mediatek: Modify mediatek-drm for mt8195 multi mmsys support")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

Reviewed-by: Chen-Yu Tsai <wenst@...omium.org>

> ---
>  drivers/gpu/drm/mediatek/mtk_drm_drv.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index e09578756de0..a8fbccb50c74 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -464,7 +464,7 @@ static int mtk_drm_kms_init(struct drm_device *drm)
>
>         ret = drmm_mode_config_init(drm);
>         if (ret)
> -               goto put_mutex_dev;
> +               return ret;
>
>         drm->mode_config.min_width = 64;
>         drm->mode_config.min_height = 64;
> @@ -483,7 +483,7 @@ static int mtk_drm_kms_init(struct drm_device *drm)
>                 drm->dev_private = private->all_drm_private[i];
>                 ret = component_bind_all(private->all_drm_private[i]->dev, drm);
>                 if (ret)
> -                       goto put_mutex_dev;
> +                       return ret;
>         }
>
>         /*
> @@ -576,9 +576,6 @@ static int mtk_drm_kms_init(struct drm_device *drm)
>  err_component_unbind:
>         for (i = 0; i < private->data->mmsys_dev_num; i++)
>                 component_unbind_all(private->all_drm_private[i]->dev, drm);
> -put_mutex_dev:
> -       for (i = 0; i < private->data->mmsys_dev_num; i++)
> -               put_device(private->all_drm_private[i]->mutex_dev);
>
>         return ret;
>  }
> @@ -649,8 +646,10 @@ static int mtk_drm_bind(struct device *dev)
>                 return 0;
>
>         drm = drm_dev_alloc(&mtk_drm_driver, dev);
> -       if (IS_ERR(drm))
> -               return PTR_ERR(drm);
> +       if (IS_ERR(drm)) {
> +               ret = PTR_ERR(drm);
> +               goto err_put_dev;
> +       }
>
>         private->drm_master = true;
>         drm->dev_private = private;
> @@ -676,6 +675,8 @@ static int mtk_drm_bind(struct device *dev)
>         drm_dev_put(drm);
>         for (i = 0; i < private->data->mmsys_dev_num; i++)
>                 private->all_drm_private[i]->drm = NULL;
> +err_put_dev:
> +       put_device(private->mutex_dev);
>         return ret;
>  }
>
> @@ -688,6 +689,8 @@ static void mtk_drm_unbind(struct device *dev)
>                 drm_dev_unregister(private->drm);
>                 mtk_drm_kms_deinit(private->drm);
>                 drm_dev_put(private->drm);
> +
> +               put_device(private->mutex_dev);
>         }
>         private->mtk_drm_bound = false;
>         private->drm_master = false;
> --
> 2.48.1
>