Re: [PATCH v3 0/3] overlayfs: debugging check for valid superblock

[Amir Goldstein]

On Sun, May 21, 2023 at 11:28 AM Andrea Righi
<andrea.righi@xxxxxxxxxxxxx> wrote:
>
> OVL_FS() is used to get a struct ovl_fs from a sturct super_block, but
> we don't have any check to determine if the superblock is valid or not.
>
> This can lead to unexpected behaviors or bugs that are pretty hard to
> track down.
>
> Add an explicit WARN_ON_ONCE() check to OVL_FS() to make sure it's
> always used with a valid overlayfs superblock.
>
> To avoid enabling this additional pendatic check everywhere, introduce
> the new config option CONFIG_OVERLAY_FS_DEBUG, that can be used in the
> future also for other additional debugging checks.
>
> Maybe a nicer solution could be to return an error from OVL_FS() when
> it's used with an invalid superblock and propagate the error in the rest
> of overlayfs code, but for now having at least the possibility to
> trigger a warning can help to catch potential bugs in advance.
>

Applied to overlayfs-next with following changes:
- open code WARN_ON_ONCE() in OVL_FS() (Miklos)
- rebase and add missing OVL_FS() accessors

Thanks,
Amir.

> Changelog (v2 -> v3):
>  - do not hide is_ovl_fs_sb() under CONFIG_OVERLAY_FS_DEBUG
>  - split consistent use of OVL_FS() and superblock validation in two
>    separate patches
>
> Changelog (v1 -> v2):
>  - replace BUG_ON() with WARN_ON_ONCE()
>  - introduce CONFIG_OVERLAY_FS_DEBUG
>
> Andrea Righi (3):
>       ovl: Kconfig: introduce CONFIG_OVERLAY_FS_DEBUG
>       ovl: make consistent use of OVL_FS()
>       ovl: validate superblock in OVL_FS()
>
>  fs/overlayfs/Kconfig     |  9 +++++++++
>  fs/overlayfs/copy_up.c   |  2 +-
>  fs/overlayfs/export.c    | 10 +++++-----
>  fs/overlayfs/inode.c     |  8 ++++----
>  fs/overlayfs/namei.c     |  2 +-
>  fs/overlayfs/ovl_entry.h | 14 ++++++++++++++
>  fs/overlayfs/super.c     | 12 ++++++------
>  fs/overlayfs/util.c      | 18 +++++++++---------
>  8 files changed, 49 insertions(+), 26 deletions(-)
>