linux-kernel - Re: [PATCH v3 3/3] ovl: validate superblock in OVL

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Message-ID: <CAOQ4uxjxSVNqicAUhevCXEuRZGZdAPhz4BksM8yE5HbE0piZ6A@mail.gmail.com>
Date:   Fri, 11 Aug 2023 12:14:40 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Miklos Szeredi <miklos@...redi.hu>,
        Andrea Righi <andrea.righi@...onical.com>
Cc:     linux-unionfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 3/3] ovl: validate superblock in OVL_FS()

On Mon, Jul 24, 2023 at 5:43 PM Miklos Szeredi <miklos@...redi.hu> wrote:
>
> On Sun, 21 May 2023 at 10:28, Andrea Righi <andrea.righi@...onical.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@...il.com>
> > Signed-off-by: Andrea Righi <andrea.righi@...onical.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)
>

Andrea,

There is an inherent challenge with a cleanup series like this one
that touches many functions to avoid merge conflicts with other
devel branches. I did not try, but I expect there are conflicts
with the current overlayfs-next branch.

I also see at least one new direct reference of sb->s_fs_info
in ovl_maybe_validate_verity().

Please make sure to base your next submission on overlayfs-next
branch from git://git.kernel.org/pub/scm/linux/kernel/git/overlayfs/vfs.git.

Once you do that, we could apply your patches to overlayfs-next
so they won't get stale again.

Thanks,
Amir.