Advisory [CVE-2026-64425] re-check IO_WQ_BIT_EXIT for each linked work item

In the Linux kernel, the following vulnerability has been resolved: io_uring/io-wq: re-check IO_WQ_BIT_EXIT for each linked work item commit 10dc95939817 ("io_uring/io-wq: check IO_WQ_BIT_EXIT inside work run loop") fixed the obvious case where io_worker_handle_work() took one exit-bit snapshot before draining pending work, but the fix stops one level too early. io_worker_handle_work() now re-checks IO_WQ_BIT_EXIT in its outer work run loop, yet it still snapshots that bit once before processing a whole dependent linked-work chain.

If io_wq_exit_start() sets IO_WQ_BIT_EXIT after the first linked item has started, the remaining linked items can still reuse stale do_kill = false, skip IO_WQ_WORK_CANCEL, and continue running after exit has begun. Move the check further inside, so it covers linked items too.

Note: this is a syzbot special as it loves setting up tons of slow linked work on weird devices like msr that take forever to read, and immediately close the ring. Exit then takes a long time.

This vulnerability allows linked work items to continue executing even after a system exit process has begun. This can lead to a denial of service by prolonging the exit sequence and potentially consuming system resources unexpectedly.

Red Hat severity: not rated. Weakness: CWE-1050.