CVE-2026-72203 ntfs: skip extent mft records in writeback to prevent deadlock
A deadlock in the Linux kernel NTFS driver can cause a system hang during file writeback operations, requiring a kernel patch to resolve.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72203?
CVE-2026-72203 is a high-severity denial of service vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ntfs: skip extent mft records in writeback to prevent deadlock
This patch fixes the ABBA deadlock between extent_lock and extent mrec_lock triggered by xfstests generic/113, that occurs since the commit 6994acf33bae ("ntfs: use base mft_no when looking up base inode for extent record").
Path A (inode writeback): VFS writeback -> ntfs_write_inode() -> __ntfs_write_inode() -> mutex_lock(&ni->extent_lock) -> mutex_lock(&tni->mrec_lock)
Path B (MFT folio writeback): VFS writeback of $MFT dirty folios -> ntfs_mft_writepages() -> ntfs_write_mft_block() -> ntfs_may_write_mft_record() -> holds one extent mrec_lock from a previous iteration -> tries to acquire another base inode extent_lock
By removing all extent_lock and extent mrec_lock acquisition from the MFT folio writeback path, the ABBA lock ordering is eliminated:
Path A: __ntfs_write_inode(): extent_lock -> mrec_lock Path B (removed): ntfs_write_mft_block(): mrec_lock -> extent_lock
Path B is always redundant for extent records because:
1. mark_mft_record_dirty(ext_ni) does NOT dirty the MFT folio. It only sets NInoDirty(ext_ni) and marks the base VFS inode dirty via __mark_inode_dirty(I_DIRTY_DATASYNC), which triggers Path A. Therefore, normal extent modifications never create a situation where the MFT folio is dirty and Path B is not scheduled.
2. The MFT folio only gets dirtied via ntfs_mft_mark_dirty() inside ntfs_mft_record_alloc(). But all identified callers in attrib.c (ntfs_attr_add, ntfs_attr_record_move_away, ntfs_attr_make_non_resident, ntfs_attr_record_resize) follow through with mark_mft_record_dirty(), which triggers Path A to write the complete record.
3. ntfs_evict_big_inode() calls ntfs_commit_inode() before freeing extent inodes, ensuring all dirty extents are flushed via Path A before the base inode leaves the icache.
Which versions are affected by CVE-2026-72203?
How do I fix CVE-2026-72203?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-72203 being exploited?
There is no known exploitation of CVE-2026-72203 in the wild and no public exploit code.
Sources
Also known as AZL-96168, BELL-CVE-2026-72203, DEBIAN-CVE-2026-72203, GHSA-p3pr-3qq8-w67c, UBUNTU-CVE-2026-72203.