CVE-2025-39878

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

ceph: fix crash after fscrypt_encrypt_pagecache_blocks() error

The function move_dirty_folio_in_page_array() was created by commit

ce80b76dd327 ("ceph: introduce ceph_process_folio_batch() method") by

moving code from ceph_writepages_start() to this function.

This new function is supposed to return an error code which is checked

by the caller (now ceph_process_folio_batch()), and on error, the

caller invokes redirty_page_for_writepage() and then breaks from the

loop.

However, the refactoring commit has gone wrong, and it by accident, it

always returns 0 (= success) because it first NULLs the pointer and

then returns PTR_ERR(NULL) which is always 0. This means errors are

silently ignored, leaving NULL entries in the page array, which may

later crash the kernel.

The simple solution is to call PTR_ERR() before clearing the pointer.