CVE-2026-64031

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

erofs: fix managed cache race for unaligned extents

After unaligned compressed extents were introduced, the following race

could occur:

[Thread 1] [Thread 2]

(z_erofs_fill_bio_vec)

<handle a Z_EROFS_PREALLOCATED_FOLIO folio>

...

filemap_add_folio (1)

(z_erofs_bind_cache)

<the same folio is found..>

..

..

folio_attach_private (2)

filemap_add_folio (3) again

Since (1) is executed but (2) hasn't been executed yet, it's possible

that another thread finds the same managed folio in z_erofs_bind_cache()

for a different pcluster and calls filemap_add_folio() again since

folio->private is still Z_EROFS_PREALLOCATED_FOLIO.

Fix this by explicitly clearing folio->private before making the folio

visible in the managed cache so that another pcluster can simply wait

on the locked managed folio as what we did for other shared cases [1].

This only impacts unaligned data compression (`-E48bit` with zstd,

for example).

[1] Commit 9e2f9d34dd12 ("erofs: handle overlapped pclusters out of

crafted images properly") was originally introduced to handle crafted

overlapped extents, but it addresses unaligned extents as well.