Linux kernel io_uring: race with linked requests causes hangs during task exit
CVE-2026-99255 Published on November 3, 2026
io_uring/io-wq: don't hide a link from cancellations
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.
Products Associated with CVE-2026-99255
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Affected Versions
Linux:- Version 768134d4f48109b90f4248feecbeeb7d684e410c and below 98470f164286f7f62aaee519d4d11b9370ce6d7b is affected.
- Version 768134d4f48109b90f4248feecbeeb7d684e410c and below d39ebc7a583d650b1d6da9b45e2ce96ad4d877e4 is affected.
- Version 768134d4f48109b90f4248feecbeeb7d684e410c and below ebe8e97fb99d9f374c482902a00677cfd24a6c27 is affected.
- Version 768134d4f48109b90f4248feecbeeb7d684e410c and below 3e02b8df0e9fa1423ac2a4e03409a9329c30ac49 is affected.
- Version 768134d4f48109b90f4248feecbeeb7d684e410c and below 92e20e9c72bdf6cfa6f84eded7b33399bc7061da is affected.
- Version 5.5 is affected.
- Before 5.5 is unaffected.
- Version 6.1.191, <= 6.1.* is unaffected.
- Version 6.6.161, <= 6.6.* is unaffected.
- Version 6.12.115, <= 6.12.* is unaffected.
- Version 6.18.60, <= 6.18.* is unaffected.
- Version 7.2.14, <= 7.2.* is unaffected.