linux-kernel - Re: [PATCH] drivers core: don't do anything in device_del() when device

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Date:   Thu, 1 Apr 2021 15:31:56 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Yufen Yu <yuyufen@...wei.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH] drivers core: don't do anything in device_del() when
 device_add() fail

On Thu, Apr 1, 2021 at 2:56 PM Yufen Yu <yuyufen@...wei.com> wrote:
>
> Recently, our syzbot test reported NULL pointer dereference in
> device_del() by injecting memory allocation fail in device_add().
>
> For now, callers of device_add(), such as add_disk(), may ignore
> device_add()'s fail and go on working. In unregister path, it will
> call device_del() from del_gendisk(). That can cause various NULL
> pointer dereference, including dev->p is NULL in kill_device(),
> 'name' is NULL in sysfs_remove_link(), kobj->sd is 'NULL' when call
> dpm_sysfs_remove(), and so on.
>
> To avoid these kernel panic, we call device_del() only when device_add()
> is success.

The patch looks reasonable to me, but the above is not what it does.

It causes device_del() to be a no-op for devices that have not been
successfully added.

> Signed-off-by: Yufen Yu <yuyufen@...wei.com>
> ---
>  drivers/base/core.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index f29839382f81..a10ec5dbc577 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3380,6 +3380,9 @@ void device_del(struct device *dev)
>         struct class_interface *class_intf;
>         unsigned int noio_flag;
>
> +       if (!dev->p)
> +               return;
> +
>         device_lock(dev);
>         kill_device(dev);
>         device_unlock(dev);
> --