In the Linux kernel, the following vulnerability has been resolved:
io_uring/io-wq: don't hide a link from cancellations
A task that exits cancels its tracked requests and waits until they are
gone. io_uring_cancel_generic() looks everywhere a request can be, and
goes to sleep if it found nothing to cancel. It is woken up each time
one of the requests of the task is completed by task work or freed.
When io-wq is done with a request that has a link, there is a time in which
the next request of the link can't be found:
io_worker_handle_work()
io_assign_current_work(worker, NULL)
io_wq_free_work(work)
io_req_find_next() // takes the link off the request
io_free_req() // task work for the task
io_assign_current_work(worker, linked)
io_run_task_work()
cond_resched()
worker->cur_work = linked
It is not pending, it is not the current work of a worker, and it is not
yet on the list that it is about to be parked on. If the pass that the
exiting task makes because of io_free_req() falls into that time, it finds
nothing and the task goes to sleep. The worker then runs the link, which
IO_WQ_BIT_EXIT doesn't prevent for bounded work. If that parks the request
nothing is completed or freed, and nobody wakes up the task. If it is the
process that exits it can't be killed any more either.
NOP, IOSQE_ASYNC | IOSQE_IO_LINK
FUTEX_WAIT, FUTEX2_PRIVATE
exit of the thread, or of the process, up to 63us later
With four of these per round 5 to 8 of 10,000 rounds hang (4 CPUs, KVM):
io_uring_cancel_generic
do_exit
Commit f8b632e89a10 ("io_uring: tighten task exit cancellations") is about
the same gap, and makes the task look again for whatever happens before
io_free_req().
Free the request once the link is the current work of the worker, or
pending. Whoever is woken up by that can find the link, until it is parked
where cancellations look as well. To do so split io_wq_free_work() in two.
io_uring/io-wq: don't hide a link from cancellations
A task that exits cancels its tracked requests and waits until they are
gone. io_uring_cancel_generic() looks everywhere a request can be, and
goes to sleep if it found nothing to cancel. It is woken up each time
one of the requests of the task is completed by task work or freed.
When io-wq is done with a request that has a link, there is a time in which
the next request of the link can't be found:
io_worker_handle_work()
io_assign_current_work(worker, NULL)
io_wq_free_work(work)
io_req_find_next() // takes the link off the request
io_free_req() // task work for the task
io_assign_current_work(worker, linked)
io_run_task_work()
cond_resched()
worker->cur_work = linked
It is not pending, it is not the current work of a worker, and it is not
yet on the list that it is about to be parked on. If the pass that the
exiting task makes because of io_free_req() falls into that time, it finds
nothing and the task goes to sleep. The worker then runs the link, which
IO_WQ_BIT_EXIT doesn't prevent for bounded work. If that parks the request
nothing is completed or freed, and nobody wakes up the task. If it is the
process that exits it can't be killed any more either.
NOP, IOSQE_ASYNC | IOSQE_IO_LINK
FUTEX_WAIT, FUTEX2_PRIVATE
exit of the thread, or of the process, up to 63us later
With four of these per round 5 to 8 of 10,000 rounds hang (4 CPUs, KVM):
io_uring_cancel_generic
do_exit
Commit f8b632e89a10 ("io_uring: tighten task exit cancellations") is about
the same gap, and makes the task look again for whatever happens before
io_free_req().
Free the request once the link is the current work of the worker, or
pending. Whoever is woken up by that can find the link, until it is parked
where cancellations look as well. To do so split io_wq_free_work() in two.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||||||||
| Linux | Linux | affected |
|
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Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Tue, 03 Nov 2026 11:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: io_uring/io-wq: don't hide a link from cancellations A task that exits cancels its tracked requests and waits until they are gone. io_uring_cancel_generic() looks everywhere a request can be, and goes to sleep if it found nothing to cancel. It is woken up each time one of the requests of the task is completed by task work or freed. When io-wq is done with a request that has a link, there is a time in which the next request of the link can't be found: io_worker_handle_work() io_assign_current_work(worker, NULL) io_wq_free_work(work) io_req_find_next() // takes the link off the request io_free_req() // task work for the task io_assign_current_work(worker, linked) io_run_task_work() cond_resched() worker->cur_work = linked It is not pending, it is not the current work of a worker, and it is not yet on the list that it is about to be parked on. If the pass that the exiting task makes because of io_free_req() falls into that time, it finds nothing and the task goes to sleep. The worker then runs the link, which IO_WQ_BIT_EXIT doesn't prevent for bounded work. If that parks the request nothing is completed or freed, and nobody wakes up the task. If it is the process that exits it can't be killed any more either. NOP, IOSQE_ASYNC | IOSQE_IO_LINK FUTEX_WAIT, FUTEX2_PRIVATE exit of the thread, or of the process, up to 63us later With four of these per round 5 to 8 of 10,000 rounds hang (4 CPUs, KVM): io_uring_cancel_generic do_exit Commit f8b632e89a10 ("io_uring: tighten task exit cancellations") is about the same gap, and makes the task look again for whatever happens before io_free_req(). Free the request once the link is the current work of the worker, or pending. Whoever is woken up by that can find the link, until it is parked where cancellations look as well. To do so split io_wq_free_work() in two. | |
| Title | io_uring/io-wq: don't hide a link from cancellations | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-11-03T11:20:13.169Z
Reserved: 2026-09-25T10:25:14.404Z
Link: CVE-2026-99255
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.