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xfs: deprecate the ascii-ci feature

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This feature is a mess -- the hash function has been broken for the
entire 15 years of its existence if you create names with extended ascii
bytes; metadump name obfuscation has silently failed for just as long;
and the feature clashes horribly with the UTF8 encodings that most
systems use today.  There is exactly one fstest for this feature.

In other words, this feature is crap.  Let's deprecate it now so we can
remove it from the codebase in 2030.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Darrick J. Wong 2023-04-11 19:05:19 -07:00
parent 6db09a8d03
commit 7ba83850ca
3 changed files with 41 additions and 0 deletions
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1
Documentation/admin-guide/xfs.rst
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@ -240,6 +240,7 @@ Deprecated Mount Options
Name Removal Schedule
=========================== ================
Mounting with V4 filesystem September 2030
Mounting ascii-ci filesystem September 2030
ikeep/noikeep September 2025
attr2/noattr2 September 2025
=========================== ================

27
fs/xfs/Kconfig
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@ -47,6 +47,33 @@ config XFS_SUPPORT_V4
To continue supporting the old V4 format (crc=0), say Y.
To close off an attack surface, say N.
config XFS_SUPPORT_ASCII_CI
bool "Support deprecated case-insensitive ascii (ascii-ci=1) format"
depends on XFS_FS
default y
help
The ASCII case insensitivity filesystem feature only works correctly
on systems that have been coerced into using ISO 8859-1, and it does
not work on extended attributes. The kernel has no visibility into
the locale settings in userspace, so it corrupts UTF-8 names.
Enabling this feature makes XFS vulnerable to mixed case sensitivity
attacks. Because of this, the feature is deprecated. All users
should upgrade by backing up their files, reformatting, and restoring
from the backup.
Administrators and users can detect such a filesystem by running
xfs_info against a filesystem mountpoint and checking for a string
beginning with "ascii-ci=". If the string "ascii-ci=1" is found, the
filesystem is a case-insensitive 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
feature will be removed entirely in September 2030. Distributors
can say N here to withdraw support earlier.
To continue supporting case-insensitivity (ascii-ci=1), 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
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@ -1548,6 +1548,19 @@ xfs_fs_fill_super(
#endif
}
/* ASCII case insensitivity is undergoing deprecation. */
if (xfs_has_asciici(mp)) {
#ifdef CONFIG_XFS_SUPPORT_ASCII_CI
xfs_warn_once(mp,
"Deprecated ASCII case-insensitivity feature (ascii-ci=1) will not be supported after September 2030.");
#else
xfs_warn(mp,
"Deprecated ASCII case-insensitivity feature (ascii-ci=1) not supported by kernel.");
error = -EINVAL;
goto out_free_sb;
#endif
}
/* Filesystem claims it needs repair, so refuse the mount. */
if (xfs_has_needsrepair(mp)) {
xfs_warn(mp, "Filesystem needs repair. Please run xfs_repair.");