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ntfs: fix off-by-one page overflow in ntfs_decompress()

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The per-token range check in ntfs_decompress() uses

	if (cb >= cb_sb_end || dp_addr > dp_sb_end)
		break;

so dp_addr == dp_sb_end falls through to the symbol copy
`*dp_addr++ = *cb++`, writing one byte past the destination page.  Since
NTFS_SB_SIZE == PAGE_SIZE the destination is a single page, so the byte
lands in the adjacent page, and *dest_ofs is left one past the sub-block
end (the later `*dest_ofs &= ~PAGE_MASK` then yields 1, not 0, so the page
is never finalized and later sub-blocks keep writing further past it).  A
corrupted compressed $DATA attribute thus produces a bounded run of
out-of-bounds writes when the file is read.

Break as soon as dp_addr reaches dp_sb_end; a full sub-block still
completes, as its final copy advances dp_addr to exactly dp_sb_end.

Fixes: 1e9ea7e044 ("Revert "fs: Remove NTFS classic"")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dennis Tighe <dennis.tighe@gmail.com>
Reviewed-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
This commit is contained in:
Dennis Tighe
2026-08-19 23:32:58 -07:00
committed by Namjae Jeon
parent 60038154b4
commit 98716c9fce
1 changed files with 1 additions and 1 deletions
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2
fs/ntfs/compress.c
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@@ -349,7 +349,7 @@ static int ntfs_decompress(struct page *dest_pages[], int completed_pages[],
u8 *dp_back_addr;
/* Check if we are done / still in range. */
if (cb >= cb_sb_end || dp_addr > dp_sb_end)
if (cb >= cb_sb_end || dp_addr >= dp_sb_end)
break;
/* Determine token type and parse appropriately.*/