# CVE-2026-99254: io_uring: don't flood a cancelling task with task_work

Status: published. Published: 2026-11-03. Updated: 2026-11-03.

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

io_uring: don't flood a cancelling task with task_work

io_ring_exit_work() asks each task which has used the ring to remove its
tctx node, by task_work, and repeats that until the list is empty.
io_tctx_exit_cb() doesn't touch the node while the task is in
io_uring_cancel_generic(), which removes all the nodes at its end. So the
work item queues the callback again as soon as it has completed, for
nothing.

That is more than a waste of time. task_work_run() only returns when it
finds the list empty. If the rings are released from inside the
cancellation, because requests of other rings held the last references to
their files, up to 64 work items keep sending callbacks to the one task
which is running them. It never finds the list empty, never gets back to
the cancellation, the nodes stay, and so it goes on: a task with 60 pairs
of rings which poll each other ran 280000 callbacks in 5 seconds, 20
seconds after exit_group(). It ends when all the senders happen to be late
at the same time. Until then the task keeps a CPU and the work items busy.

An exiting task can't be killed meanwhile. execve() cancels the requests in
the same way, so a live task can get stuck there as well, for minutes. If
it takes more than five, the work items run into the
WARN_ON_ONCE(time_after(jiffies, timeout)) of io_ring_exit_work(). No
privilege is needed for any of this.

If the callback has met a task in cancellation, wait a little before it is
sent again. Nobody has to wake the work item up for that: either the node
is gone by then, or it is the turn of the next round.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ d56d938b4bef3e1421a42023cdcd6e13c1f50831; < a22fb44e988b01b82235ea07f0bf0fc73e256596 (affected, git); ≥ d56d938b4bef3e1421a42023cdcd6e13c1f50831; < 2c75ebae8a7f09c99e31c7042b7d4d595f03b2b1 (affected, git); ≥ d56d938b4bef3e1421a42023cdcd6e13c1f50831; < 61c761fc21e00e45c33c2bb596be442d92fb8792 (affected, git); ≥ d56d938b4bef3e1421a42023cdcd6e13c1f50831; < 14f56e9c0b8fdc2e178acdbec9781e90ef46f7e9 (affected, git); ≥ d56d938b4bef3e1421a42023cdcd6e13c1f50831; < abdc57c7ebabaaf0b622178a6a85834e1e54ff80 (affected, git). Source: CNA: Linux
- Linux / Linux: 5.12 (affected); ≥ 0; < 5.12 (unaffected, semver); ≥ 6.1.191; ≤ 6.1.* (unaffected, semver); ≥ 6.6.161; ≤ 6.6.* (unaffected, semver); ≥ 6.12.115; ≤ 6.12.* (unaffected, semver); ≥ 6.18.60; ≤ 6.18.* (unaffected, semver); ≥ 7.2.14; ≤ 7.2.* (unaffected, semver). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/a22fb44e988b01b82235ea07f0bf0fc73e256596 (CNA: Linux)

- https://git.kernel.org/stable/c/2c75ebae8a7f09c99e31c7042b7d4d595f03b2b1 (CNA: Linux)

- https://git.kernel.org/stable/c/61c761fc21e00e45c33c2bb596be442d92fb8792 (CNA: Linux)

- https://git.kernel.org/stable/c/14f56e9c0b8fdc2e178acdbec9781e90ef46f7e9 (CNA: Linux)

- https://git.kernel.org/stable/c/abdc57c7ebabaaf0b622178a6a85834e1e54ff80 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-99254; retrieved 2026-11-03; source updated 2026-11-03

Revision: 3c1a3325ef7b97a4cb966cbb6af583860f30c6cea5e4b9daf4828e7d5b63cbba

Canonical: https://y2.dev/cve/CVE-2026-99254

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