Bug 2448691 (CVE-2026-23267)

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

f2fs: fix IS_CHECKPOINTED flag inconsistency issue caused by concurrent atomic commit and checkpoint writes

During SPO tests, when mounting F2FS, an -EINVAL error was returned from
f2fs_recover_inode_page. The issue occurred under the following scenario

Thread A                                     Thread B
f2fs_ioc_commit_atomic_write
 - f2fs_do_sync_file // atomic = true
  - f2fs_fsync_node_pages
    : last_folio = inode folio
    : schedule before folio_lock(last_folio) f2fs_write_checkpoint
                                              - block_operations// writeback last_folio
                                              - schedule before f2fs_flush_nat_entries
    : set_fsync_mark(last_folio, 1)
    : set_dentry_mark(last_folio, 1)
    : folio_mark_dirty(last_folio)
    - __write_node_folio(last_folio)
      : f2fs_down_read(&sbi->node_write)//block
                                              - f2fs_flush_nat_entries
                                                : {struct nat_entry}->flag |= BIT(IS_CHECKPOINTED)
                                              - unblock_operations
                                                : f2fs_up_write(&sbi->node_write)
                                             f2fs_write_checkpoint//return
      : f2fs_do_write_node_page()
f2fs_ioc_commit_atomic_write//return
                                             SPO

Thread A calls f2fs_need_dentry_mark(sbi, ino), and the last_folio has
already been written once. However, the {struct nat_entry}->flag did not
have the IS_CHECKPOINTED set, causing set_dentry_mark(last_folio, 1) and
write last_folio again after Thread B finishes f2fs_write_checkpoint.

After SPO and reboot, it was detected that {struct node_info}->blk_addr
was not NULL_ADDR because Thread B successfully write the checkpoint.

This issue only occurs in atomic write scenarios. For regular file
fsync operations, the folio must be dirty. If
block_operations->f2fs_sync_node_pages successfully submit the folio
write, this path will not be executed. Otherwise, the
f2fs_write_checkpoint will need to wait for the folio write submission
to complete, as sbi->nr_pages[F2FS_DIRTY_NODES] > 0. Therefore, the
situation where f2fs_need_dentry_mark checks that the {struct
nat_entry}->flag /wo the IS_CHECKPOINTED flag, but the folio write has
already been submitted, will not occur.

Therefore, for atomic file fsync, sbi->node_write should be acquired
through __write_node_folio to ensure that the IS_CHECKPOINTED flag
correctly indicates that the checkpoint write has been completed.