Bug 2536564 (CVE-2026-90200) - CVE-2026-90200 kernel: fs/ntfs3: fix integer overflow in MFT cluster validation
Summary: CVE-2026-90200 kernel: fs/ntfs3: fix integer overflow in MFT cluster validation
Keywords:
Status: NEW
Alias: CVE-2026-90200
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
medium
medium
Target Milestone: ---
Assignee: Product Security
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-09-17 18:26 UTC by OSIDB Bzimport
Modified: 2026-10-13 13:15 UTC (History)
17 users (show)

Fixed In Version:
Clone Of:
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Last Closed:
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Description OSIDB Bzimport 2026-09-17 18:26:04 UTC
In the Linux kernel, the following vulnerability has been resolved:

fs/ntfs3: fix integer overflow in MFT cluster validation

In ntfs_init_from_boot(), the boot sector's MFT cluster numbers are
validated against the volume size with:

	if (mlcn  * sct_per_clst >= sectors ||
	    mlcn2 * sct_per_clst >= sectors)
		goto out;

mlcn and mlcn2 are u64 fields read directly from the boot sector.
sct_per_clst is bounded above by 4096 (true_sectors_per_clst() plus
the is_power_of_2() check below it), but the multiplication is done
in u64 and wraps when mlcn (or mlcn2) is large enough -- e.g. mlcn
near 2^62 with sct_per_clst == 4 wraps to 0, which compares below
any non-zero 'sectors', so the check is bypassed and the malformed
record is accepted.

The accepted mlcn is then used unchanged in

	sbi->mft.lbo = mlcn << cluster_bits;

In practice the resulting reads fail at the block layer (sb_bread()
returns NULL via grow_buffers()'s check_mul_overflow() guard), so
today this manifests as mount failing in odd places rather than as
something more dangerous, but the validation step is still wrong
and there is no reason for callers to rely on the block layer to
catch a value that should never have been accepted in the first
place.

Use check_mul_overflow() to compute the two sector positions and
fail the mount if either multiplication wraps; this preserves the
existing semantics (mlcn * sct_per_clst >= sectors) instead of
switching to division (mlcn >= sectors / sct_per_clst), which
would tighten the check at edge cases where 'sectors' is not a
multiple of sct_per_clst.  The check_*_overflow() style is the
one ntfs3 already uses for similar on-disk arithmetic in
fs/ntfs3/run.c.


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