In the Linux kernel, the following vulnerability has been resolved: md/md-llbitmap: stop daemon timer rearm on destroy llbitmap_destroy() deletes pending_timer before flushing md_llbitmap_io_wq

Overview

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

md/md-llbitmap: stop daemon timer rearm on destroy

llbitmap_destroy() deletes pending_timer before flushing md_llbitmap_io_wq. However, daemon_work can still be queued or running after the timer has been deleted, and the daemon path can arm pending_timer again when it finds dirty chunks that are not ready to flush yet.

If that happens during teardown, pending_timer can remain armed after llbitmap is freed and later dereference freed memory.

Add a BITMAP_SHUTDOWN bit to llbitmap->flags, set it before deleting the timer, and make the timer and daemon paths stop queueing or rearming work once teardown starts. Cancel daemon_work before flushing the shared workqueue so no already queued daemon instance can race with the free. Use timer_shutdown_sync() so a daemon instance that passed the shutdown check before teardown cannot rearm the timer afterward.

BITMAP_SHUTDOWN is a runtime-only state. Mask it out when reading and updating the llbitmap superblock so the shutdown state is never loaded from disk or persisted to disk.

Remediation

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