CVE-2026-99243

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CVE-2026-99243

Summary: io-wq: order the exit bit against worker creation task work

Details: In the Linux kernel, the following vulnerability has been resolved: io-wq: order the exit bit against worker creation task work io_wq_exit_workers() cancels task work for queued worker creation with task_work_cancel_match(). That has a plain load of task->task_works. io_queue_worker_create() adds the new entry and tests IO_WQ_BIT_EXIT to cancel it if the workqueue is already on its way out. That must be ordered. task_work_add() has a full barrier via cmpxchg(). But io_wq_exit_start() sets the bit with set_bit() which doesn't have any memory ordering. So afaict, on weakly ordered architectures the exiting task may load task_works before the store of the bit is visible. The other side tests the bit before the store is visible as well. So the entry remains queued with worker_refs and the exiting task waits on worker_done indefinitely. If the task still has rings then io_uring_del_tctx_node() provides the barrier via test_and_set_bit() in io_wq_set_exit_on_idle(). When it has closed all rings though that barrier is gone. Add the barrier after the set_bit().

References: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git, https://git.kernel.org/stable/c/0d81cdd433b0a96c5275c01b8172e0b1f71dd595, https://git.kernel.org/stable/c/0e5663856b69219ef2f02e04bac9f5c5be19718a, https://git.kernel.org/stable/c/1432d881d99584105122760133caeff1dce7a9f7, https://git.kernel.org/stable/c/31fc780b75b278d37700373d54a99fdb4117fdd6, https://git.kernel.org/stable/c/67da3eec264aeb67835886720243ae2dc1463315, https://git.kernel.org/stable/c/6cf012a4d5e461c788ecc9dbed67adc31a142644, https://git.kernel.org/stable/c/75395db7a9b40a2e826c838e648fef8ed1a2d174, https://git.kernel.org/stable/c/a63c752157eacf49f628359822666b32503d194a, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/99xxx/CVE-2026-99243.json, https://nvd.nist.gov/vuln/detail/CVE-2026-99243