CVE-2026-53017
Description
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.
Summary dbcve.org
A race condition in f2fs filesystem allows data loss when fsync is performed on a newly created file concurrently with checkpoint. The function f2fs_need_inode_block_update() incorrectly relies on IS_CHECKPOINTED and HAS_LAST_FSYNC nat_entry flags set during checkpoint to determine if inode blocks need updating, but these flags don't guarantee the checkpoint has actually completed. The fix acquires sbi->node_write lock before reading these flags.
Mitigation
Apply the upstream kernel patch to f2fs_need_inode_block_update() to acquire node_write lock before reading nat_entry flags, ensuring checkpoint completion is properly synchronized.