Withdrawn by the publisher.

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.

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.

kernel-devel-7.2.7-1.1 on GA media

Affected: Ubuntu:16.04:LTS: linux-hwe-edge, Ubuntu:18.04:LTS: linux-aws-5.0, Ubuntu:18.04:LTS: linux-aws-5.3, Ubuntu:18.04:LTS: linux-azure, Ubuntu:18.04:LTS: linux-azure-5.3, Ubuntu:18.04:LTS: linux-azure-edge, Ubuntu:18.04:LTS: linux-gcp, Ubuntu:18.04:LTS: linux-gcp-5.3, Ubuntu:18.04:LTS: linux-gke-4.15, Ubuntu:18.04:LTS: linux-gke-5.4 and 96 more

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.