In the Linux kernel, the following vulnerability has been resolved: f2fs: fix fsck inconsistency caused by incorrect nat_entry flag usage

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

f2fs: fix fsck inconsistency caused by incorrect nat_entry flag usage

f2fs_need_dentry_mark() reads nat_entry flags without mutual exclusion
with the checkpoint path, which can result in an incorrect inode block
marking state. The scenario is as follows:

create & write & fsync 'file A' write checkpoint

• f2fs_do_sync_file // inline inode
• f2fs_write_inode // inode folio is dirty
  - f2fs_write_checkpoint
  - f2fs_flush_merged_writes
  - f2fs_sync_node_pages
• f2fs_fsync_node_pages // no dirty node
• f2fs_need_inode_block_update // return true
• f2fs_fsync_node_pages // inode dirtied
• f2fs_need_dentry_mark //return true
  - f2fs_flush_nat_entries
  - f2fs_write_checkpoint end
• __write_node_folio // inode with DENT_BIT_SHIFT set
  SPO, "fsck --dry-run" find inode has already checkpointed but still
  with DENT_BIT_SHIFT set

The state observed by f2fs_need_dentry_mark() can differ from the state
observed in __write_node_folio() after acquiring sbi->node_write. The
root cause is that the semantics of IS_CHECKPOINTED and
HAS_FSYNCED_INODE are only guaranteed after the checkpoint write has
fully completed.

This patch moves set_dentry_mark() into __write_node_folio() and
protects it with the sbi->node_write lock.