ntfs: skip extent mft records in writeback to prevent deadlock

Overview

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.

Affected

• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6626fb859f4c4772f2f59751d23937716e03f98f
• Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 7ffa8f3d30236e0ab897c30bdb01224ff1fe1c89
• Linux >= 1e9ea7e04472d4e5e12e58c881eaacfb3e49b669 < f831ab09d521898bf1dd99bf5adfd630ea1428e3
• Linux >= 1e9ea7e04472d4e5e12e58c881eaacfb3e49b669 < 76bc14c7097ff678b2b5dbfd4fa33b46897d87ce
• Linux 2.6.12
• Linux 7.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.