CVE-2026-90117

In the Linux kernel, the following vulnerability has been resolved:

ntfs: validate usa_ofs before preserving the update sequence number

When ntfs_mft_record_alloc() reuses a free mft record it reads the old

update sequence number straight from the on-disk record:

usn = *(__le16 *)((u8 *)m + le16_to_cpu(m->usa_ofs));

Here m points into the raw $MFT page-cache folio, which still holds

unvalidated, MST-protected bytes: the folio is read by a plain

iomap_read_folio() and neither post_read_mst_fixup() nor

ntfs_mft_record_check() has run on it (both work on private copies).

m->usa_ofs is therefore an untrusted u16, and a corrupted record can put

it past the end of the record so the two-byte read lands outside the

folio. Reading such a record while creating a file gives, under KASAN:

BUG: KASAN: use-after-free in ntfs_mft_record_alloc+...

Read of size 2 at addr ...

ntfs_mft_record_alloc -> __ntfs_create -> ntfs_create -> path_openat

Only preserve the old update sequence number when usa_ofs is even and in

range, mirroring the check ntfs_mft_record_check() already applies;

otherwise leave usn zero, which the existing restore below skips.