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References: <20230521082813.17025-1-andrea.righi@canonical.com> <20230521082813.17025-4-andrea.righi@canonical.com>
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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Mon, 24 Jul 2023 16:43:06 +0200
Message-ID: <CAJfpegtK=dh0yNdvxSC8YF6vOYqGPM5EOWny07jYDdFc0qfhTQ@mail.gmail.com>
Subject: Re: [PATCH v3 3/3] ovl: validate superblock in OVL_FS()
To:     Andrea Righi <andrea.righi@canonical.com>
Cc:     Amir Goldstein <amir73il@gmail.com>, linux-unionfs@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Sun, 21 May 2023 at 10:28, Andrea Righi <andrea.righi@canonical.com> wrote:
>
> When CONFIG_OVERLAY_FS_DEBUG is enabled add an explicit check to make
> sure that OVL_FS() is always used with a valid overlayfs superblock.
> Otherwise trigger a WARN_ON_ONCE().
>
> Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
> ---
>  fs/overlayfs/ovl_entry.h | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index b32c38fdf3c7..e156649d9c71 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -97,8 +97,20 @@ static inline struct mnt_idmap *ovl_upper_mnt_idmap(struct ovl_fs *ofs)
>
>  extern struct file_system_type ovl_fs_type;
>
> +static inline bool is_ovl_fs_sb(struct super_block *sb)
> +{
> +       return sb->s_type == &ovl_fs_type;
> +}
> +
> +#ifdef CONFIG_OVERLAY_FS_DEBUG
> +#define OVL_VALIDATE_SB(__sb)  WARN_ON_ONCE(!is_ovl_fs_sb(__sb))
> +#else
> +#define OVL_VALIDATE_SB(__sb)
> +#endif
> +
>  static inline struct ovl_fs *OVL_FS(struct super_block *sb)
>  {
> +       OVL_VALIDATE_SB(sb);

This could be written simply and naturally:

    if (IS_ENABLED(CONFIG_OVERLAY_FS_DEBUG))
         WARN_ON_ONCE(sb->s_type != &ovl_fs_type)

Thanks,
Miklos