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xfs: deprecate the V4 format

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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: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
This commit is contained in:
Darrick J. Wong 2020-09-10 10:57:17 -07:00
parent d4f2c14cc9
commit b96cb835e3
3 changed files with 60 additions and 0 deletions
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23
Documentation/admin-guide/xfs.rst
View File

@ -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
=========================== ================

24
fs/xfs/Kconfig
View File

@ -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

13
fs/xfs/xfs_super.c
View File

@ -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