CVE-2026-53017

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

f2fs: fix data loss caused by incorrect use of nat_entry flag

Data loss can occur when fsync is performed on a newly created file

(before any checkpoint has been written) concurrently with a checkpoint

operation. 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_flush_nat_entries

- f2fs_fsync_node_pages // no dirty node

- f2fs_need_inode_block_update // return false

SPO and lost 'file A'

f2fs_flush_nat_entries() sets the IS_CHECKPOINTED and HAS_LAST_FSYNC

flags for the nat_entry, but this does not mean that the checkpoint has

actually completed successfully. However, f2fs_need_inode_block_update()

checks these flags and incorrectly assumes that the checkpoint has

finished.

The root cause is that the semantics of IS_CHECKPOINTED and

HAS_LAST_FSYNC are only guaranteed after the checkpoint write fully

completes.

This patch modifies f2fs_need_inode_block_update() to acquire the

sbi->node_write lock before reading the nat_entry flags, ensuring that

once IS_CHECKPOINTED and HAS_LAST_FSYNC are observed to be set, the

checkpoint operation has already completed.