Commit b96cb835 authored by Darrick J. Wong's avatar Darrick J. Wong
Browse files

xfs: deprecate the V4 format 



The V4 filesystem format contains known weaknesses in the on-disk format
that make metadata verification diffiult.  In addition, the format does
not support dates past 2038 and will not be upgraded to do so.  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.  Dates for these events have been added to
the upstream kernel.

Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarEric Sandeen <sandeen@redhat.com>
parent d4f2c14c

Documentation/admin-guide/xfs.rst

+23 −0
Original line number Diff line number Diff line
@@ -210,6 +210,28 @@ When mounting an XFS filesystem, the following options are accepted. 
	inconsistent namespace presentation during or after a

	failover event.



Deprecation of V4 Format

========================



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.



Administrators and users can detect a V4 filesystem by running xfs_info

against a filesystem mountpoint and checking for a string containing

"crc=".  If no such string is found, please upgrade xfsprogs to the

latest version and try again.



The deprecation will take place in two parts.  Support for mounting V4

filesystems can now be disabled at kernel build time via Kconfig option.

The option will default to yes until September 2025, at which time it

will be changed to default to no.  In September 2030, support will be

removed from the codebase entirely.



Note: Distributors may choose to withdraw V4 format support earlier than

the dates listed above.



Deprecated Mount Options

========================
@@ -217,6 +239,7 @@ Deprecated Mount Options 
===========================     ================

  Name				Removal Schedule

===========================     ================

Mounting with V4 filesystem     September 2030

===========================     ================

fs/xfs/Kconfig

+24 −0
Original line number Diff line number Diff line
@@ -22,6 +22,30 @@ 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 (crc=0) 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.



	  Administrators and users can detect a V4 filesystem by running

	  xfs_info against a filesystem mountpoint and checking for a string

	  beginning with "crc=".  If the string "crc=0" is found, the

	  filesystem is a V4 filesystem.  If no such string is found, please

	  upgrade xfsprogs to the latest version and try again.



	  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 (crc=0), say Y.

	  To close off an attack surface, say N.



config XFS_QUOTA

	bool "XFS Quota support"

	depends on XFS_FS

fs/xfs/xfs_super.c

+13 −0
Original line number Diff line number Diff line
@@ -1450,6 +1450,19 @@ xfs_fc_fill_super( 
	if (error)

		goto out_free_sb;



	/* V4 support is undergoing deprecation. */

	if (!xfs_sb_version_hascrc(&mp->m_sb)) {

#ifdef CONFIG_XFS_SUPPORT_V4

		xfs_warn_once(mp,

	"Deprecated V4 format (crc=0) will not be supported after September 2030.");

#else

		xfs_warn(mp,

	"Deprecated V4 format (crc=0) not supported by kernel.");

		error = -EINVAL;

		goto out_free_sb;

#endif

	}



	/*

	 * XFS block mappings use 54 bits to store the logical block offset.

	 * This should suffice to handle the maximum file size that the VFS

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