ceph: do not propagate page array emplacement errors as batch errors

Overview

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

ceph: do not propagate page array emplacement errors as batch errors

When fscrypt is enabled, move_dirty_folio_in_page_array() may fail because it needs to allocate bounce buffers to store the encrypted versions of each folio. Each folio beyond the first allocates its bounce buffer with GFP_NOWAIT. Failures are common (and expected) under this allocation mode; they should flush (not abort) the batch.

However, ceph_process_folio_batch() uses the same rc variable for its own return code and for capturing the return codes of its routine calls; failing to reset rc back to 0 results in the error being propagated out to the main writeback loop, which cannot actually tolerate any errors here: once ceph_wbc.pages is allocated, it must be passed to ceph_submit_write() to be freed. If it survives until the next iteration (e.g. due to the goto being followed), ceph_allocate_page_array()'s BUG_ON() will oops the worker.

Note that this failure mode is currently masked due to another bug (addressed next in this series) that prevents multiple encrypted folios from being selected for the same write.

For now, just reset rc when redirtying the folio to prevent errors in move_dirty_folio_in_page_array() from propagating. Note that move_dirty_folio_in_page_array() is careful never to return errors on the first folio, so there is no need to check for that. After this change, ceph_process_folio_batch() no longer returns errors; its only remaining failure indicator is locked_pages == 0, which the caller already handles correctly.

Affected

• Linux >= ce80b76dd32764cc914975777e058d4fae4f0ea0 < 746840c87d76b614b14d9337c466ff022fc49823
• Linux >= ce80b76dd32764cc914975777e058d4fae4f0ea0 < 4c0d84c788d89c167abf0bf84fd37890c4c84f08
• Linux >= ce80b76dd32764cc914975777e058d4fae4f0ea0 < 707104682e3c163f7c14cdd6b07a3e95fb374759
• Linux 0f2b2b7cacf888229cec19126e6791b11fb35f32
• Linux >= 6.12.114 < 6.13
• Linux 6.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.