In the Linux kernel, the following vulnerability has been resolved:
f2fs: only redirty pinned folios in redirty_blocks
redirty_blocks() pins folios with read_cache_folio() and then walks the
same range again with filemap_lock_folio() to redirty them and drop the
references it took.
Commit 5951fee46bef (“f2fs: Use a folio in redirty_blocks()”) changed
the second pass to a do/while loop. If read_cache_folio() fails before
anything is pinned, page_idx does not advance but the cleanup loop still
runs once.
If readahead has already populated the failed folio in page cache, that
extra iteration finds it and folio_put_refs(folio, 2) drops one
reference too many. Later drop_caches or reclaim can then report
“BUG: Bad page state”.
Only redirty the range that was pinned successfully.
