ntfs: fix undefined behavior in mft/index record size calculation

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The boot sector validation allows clusters_per_mft_record and
clusters_per_index_record to range from 0xE1 (-31) to 0xF7 (-9) when
interpreted as signed values. When these are used as negative shift
counts in expressions like `1 << -clusters_per_mft_record`, values
like 0xE1 cause `1 << 31`, which shifts into the sign bit of a 32-bit
signed integer, resulting in undefined behavior.

Fix by using unsigned shift (1U << ...) instead of signed shift.
This prevents undefined behavior while preserving the full valid
range of negative values (-31 to -9) that may appear in NTFS boot
sectors.

The encoding scheme uses negative values to represent record sizes
smaller than cluster_size: -log2(record_size). Common values include
-10 (1024 bytes) for mft_record_size and -12 (4096 bytes) for
index_record_size.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Hongling Zeng <zenghongling@kylinos.cn>
Reviewed-by: Baolin Liu <liubaolin@kylinos.cn>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

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Hongling Zeng 2026-08-25 17:54:05 +08:00 • committed by Namjae Jeon

parent 607a947883

commit a79899ca38

1 changed files with 2 additions and 2 deletions

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fs/ntfs/super.c

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