workqueue: Fix NULL current_pwq deref in chained work check

Overview

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

workqueue: Fix NULL current_pwq deref in chained work check

current_wq_worker() only tells us that %current is a kworker. It does not guarantee that the worker is currently executing a work item, as worker->current_pwq is populated only while process_one_work() is running the work function.

is_chained_work() can be reached while queueing on a draining or destroying workqueue. If a kworker outside work-item execution reaches that path, current_wq_worker() returns a worker but worker->current_pwq is NULL, and the chained-work test can fault before it emits the intended warning.

Guard the chained-work test with worker->current_pwq. A kworker without current_pwq is not executing work on the target workqueue, so the helper should return false and let the draining/destroying warning fire.

Affected

• Linux >= 8d03ecfe471802d6afe97da97722b6924533aa82 < 3dc61af2998cfc7312d6e59bbdcd5eed074483f2
• Linux >= 8d03ecfe471802d6afe97da97722b6924533aa82 < 729d576df89c7e4341e58c452f8890620a610ac2
• Linux >= 8d03ecfe471802d6afe97da97722b6924533aa82 < b12a25fb2b9d5dac80e419d695450cc17a51fdfd
• Linux >= 8d03ecfe471802d6afe97da97722b6924533aa82 < 1a2668682e998039a027796b236319b380078a6a
• Linux >= 8d03ecfe471802d6afe97da97722b6924533aa82 < 980db94e3eeefdd8a1c46f86412c33a7f7806f51
• Linux 3.9

Remediation

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