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Back in the 6.2-rc1 days, Eric Whitney reported a fstests regression in ext4 against generic/454. The cause of this test failure was the unfortunate combination of setting an xattr name containing UTF8 encoded emoji, an xattr hash function that accepted a char pointer with no explicit signedness, signed type extension of those chars to an int, and the 6.2 build tools maintainers deciding to mandate -funsigned-char across the board. As a result, the ondisk extended attribute structure written out by 6.1 and 6.2 were not the same. This discrepancy, in fact, had been noticeable if a filesystem with such an xattr were moved between any two architectures that don't employ the same signedness of a raw "char" declaration. The only reason anyone noticed is that x86 gcc defaults to signed, and no such -funsigned-char update was made to e2fsprogs, so e2fsck immediately started reporting data corruption. After a day and a half of discussing how to handle this use case (xattrs with bit 7 set anywhere in the name) without breaking existing users, Linus merged his own patch and didn't tell the maintainer. None of the ext4 developers realized this until AUTOSEL announced that the commit had been backported to stable. In the end, this problem could have been detected much earlier if there had been any useful tests of hash function(s) in use inside ext4 to make sure that they always produce the same outputs given the same inputs. The XFS dirent/xattr name hash takes a uint8_t*, so I don't think it's vulnerable to this problem. However, let's avoid all this drama by adding our own self test to check that the da hash produces the same outputs for a static pile of inputs on various platforms. This enables us to fix any breakage that may result in a controlled fashion. The buffer and test data are identical to the patches submitted to xfsprogs. Link: https://lore.kernel.org/linux-ext4/Y8bpkm3jA3bDm3eL@debian-BULLSEYE-live-builder-AMD64/ Link: https://lore.kernel.org/linux-xfs/ZBUKCRR7xvIqPrpX@destitution/T/#md38272cc684e2c0d61494435ccbb91f022e8dee4 Signed-off-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Dave Chinner <dchinner@redhat.com>
13 lines
276 B
C
13 lines
276 B
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2023 Oracle. All Rights Reserved.
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* Author: Darrick J. Wong <djwong@kernel.org>
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*/
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#ifndef __XFS_DAHASH_TEST_H__
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#define __XFS_DAHASH_TEST_H__
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int xfs_dahash_test(void);
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#endif /* __XFS_DAHASH_TEST_H__ */
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