On Thu, Sep 10, 2020 at 03:47:21PM -0500, Eric Sandeen wrote:
> On 9/10/20 1:27 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> >
> > The V4 filesystem format contains known weaknesses in the on-disk format
> > that make metadata verification diffiult. In addition, the format will
> > does not support dates past 2038 and will not be upgraded to do so.
> > Therefore, we should start the process of retiring the old format to
> > close off attack surfaces and to encourage users to migrate onto V5.
> >
> > Therefore, make XFS V4 support a configurable option. For the first
> > period it will be default Y in case some distributors want to withdraw
> > support early; for the second period it will be default N so that anyone
> > who wishes to continue support can do so; and after that, support will
> > be removed from the kernel.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > fs/xfs/Kconfig | 18 ++++++++++++++++++
> > fs/xfs/xfs_mount.c | 11 +++++++++++
> > 2 files changed, 29 insertions(+)
> >
> > diff --git a/fs/xfs/Kconfig b/fs/xfs/Kconfig
> > index e685299eb3d2..db54ca9914c7 100644
> > --- a/fs/xfs/Kconfig
> > +++ b/fs/xfs/Kconfig
> > @@ -22,6 +22,24 @@ config XFS_FS
> > system of your root partition is compiled as a module, you'll need
> > to use an initial ramdisk (initrd) to boot.
> >
> > +config XFS_SUPPORT_V4
> > + bool "Support deprecated V4 format"
> > + default y
> > + help
> > + The V4 filesystem format lacks certain features that are supported
> > + by the V5 format, such as metadata checksumming, strengthened
> > + metadata verification, and the ability to store timestamps past the
> > + year 2038. Because of this, the V4 format is deprecated. All users
> > + should upgrade by backing up their files, reformatting, and restoring
> > + from the backup.
>
> As Arekm pointed out, nobody outside of our clique knows what "V4" and "V5" means.
>
> (there is no mention of such things in the mkfs.xfs(8) or xfs(5), for example)
>
> admin-facing statements should probably reference CRC capability, not "V4/5"
Ok. "Deprecated V4 format (crc=0) not supported by kernel." then.
--D
> -Eric
>
> > + This option will become default N in September 2025. Support for the
> > + V4 format will be removed entirely in September 2030. Distributors
> > + can say N here to withdraw support earlier.
> > +
> > + To continue supporting the old V4 format, say Y.
> > + To close off an attack surface, say N.
> > +
> > config XFS_QUOTA
> > bool "XFS Quota support"
> > depends on XFS_FS
> > diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> > index ed69c4bfda71..48c0175b9457 100644
> > --- a/fs/xfs/xfs_mount.c
> > +++ b/fs/xfs/xfs_mount.c
> > @@ -315,6 +315,17 @@ xfs_readsb(
> > goto release_buf;
> > }
> >
> > +#ifndef CONFIG_XFS_SUPPORT_V4
> > + /* V4 support is undergoing deprecation. */
> > + if (!xfs_sb_version_hascrc(sbp)) {
> > + if (loud)
> > + xfs_warn(mp,
> > + "Deprecated V4 format not supported by kernel.");
> > + error = -EINVAL;
> > + goto release_buf;
> > + }
> > +#endif
> > +
> > /*
> > * We must be able to do sector-sized and sector-aligned IO.
> > */
> >
