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| author | Dennis Tighe <dennis.tighe@gmail.com> | 2026-08-20 19:28:39 +0900 |
|---|---|---|
| committer | Namjae Jeon <linkinjeon@kernel.org> | 2026-08-20 19:29:39 +0900 |
| commit | 81684340963da2e898eabb8c1e274433d9375bc6 (patch) | |
| tree | aab4ee5b80650ed87ec6b15aad53071529ba8929 /fs/ntfs | |
| parent | 98716c9fce21f6c8a9d71e08cf53e7504fa562f4 (diff) | |
| download | linux-81684340963da2e898eabb8c1e274433d9375bc6.tar.gz linux-81684340963da2e898eabb8c1e274433d9375bc6.zip | |
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.
Fixes: 495e90fa3348 ("ntfs: update attrib operations")
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>
Diffstat (limited to 'fs/ntfs')
| -rw-r--r-- | fs/ntfs/mft.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/fs/ntfs/mft.c b/fs/ntfs/mft.c index f95e433885a0..984a0827f9ac 100644 --- a/fs/ntfs/mft.c +++ b/fs/ntfs/mft.c @@ -2333,7 +2333,17 @@ mft_rec_already_initialized: * wrong with the previous mft record. */ seq_no = m->sequence_number; - usn = *(__le16 *)((u8 *)m + le16_to_cpu(m->usa_ofs)); + /* + * The mft record still holds unvalidated, MST-protected on-disk + * bytes, so m->usa_ofs is untrusted here. Only preserve the old + * update sequence number if that offset is in bounds; otherwise + * leave usn zero so it is not restored below. + */ + if (!(le16_to_cpu(m->usa_ofs) & 1) && + le16_to_cpu(m->usa_ofs) + sizeof(usn) <= vol->mft_record_size) + usn = *(__le16 *)((u8 *)m + le16_to_cpu(m->usa_ofs)); + else + usn = 0; err = ntfs_mft_record_layout(vol, bit, m); if (unlikely(err)) { ntfs_error(vol->sb, "Failed to layout allocated mft record 0x%llx.", |