io_uring/cancel: rearm local work wake up before sleep
io_uring_try_cancel_requests() sets ->cq_wait_nr to 1 so that the next
io_req_local_work_add() wakes the cancelling task. The add that takes the
count to zero is the only one that wakes, later ones see a count <= 0 and
return. io_uring_cancel_generic() however only becomes
TASK_INTERRUPTIBLE much later, so the one wake up can be spent on a
running task. That is fine as long as the entry of that add is still
queued, as the io_local_work_pending() check then skips the sleep. It is
not if the add was delayed after queueing its entry:
CPU0 (submitter in exec or exit) CPU1 (io_req_local_work_add)
mpscq_push(req A)
io_uring_try_cancel_requests()
io_run_local_work() // runs req A
io_uring_try_cancel_requests()
atomic_set(&ctx->cq_wait_nr, 1)
atomic_read(&ctx->cq_wait_nr) == 1
count taken, wake_up_state()
// task is running, no-op
prepare_to_wait(TASK_INTERRUPTIBLE)
io_local_work_pending() == false
schedule()
mpscq_push(req B)
cq_wait_nr <= 0, return
Only the sleeping task can run req B, so it is stuck in execve() until a
signal happens to wake it. An exiting task doesn't even get that.
Arm the count again once the task state is set and before the work list
is checked, for the rings whose local work this task is the one to run.
Analysis
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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 |
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| Linux | Linux | affected |
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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/cancel: rearm local work wake up before sleep io_uring_try_cancel_requests() sets ->cq_wait_nr to 1 so that the next io_req_local_work_add() wakes the cancelling task. The add that takes the count to zero is the only one that wakes, later ones see a count <= 0 and return. io_uring_cancel_generic() however only becomes TASK_INTERRUPTIBLE much later, so the one wake up can be spent on a running task. That is fine as long as the entry of that add is still queued, as the io_local_work_pending() check then skips the sleep. It is not if the add was delayed after queueing its entry: CPU0 (submitter in exec or exit) CPU1 (io_req_local_work_add) mpscq_push(req A) io_uring_try_cancel_requests() io_run_local_work() // runs req A io_uring_try_cancel_requests() atomic_set(&ctx->cq_wait_nr, 1) atomic_read(&ctx->cq_wait_nr) == 1 count taken, wake_up_state() // task is running, no-op prepare_to_wait(TASK_INTERRUPTIBLE) io_local_work_pending() == false schedule() mpscq_push(req B) cq_wait_nr <= 0, return Only the sleeping task can run req B, so it is stuck in execve() until a signal happens to wake it. An exiting task doesn't even get that. Arm the count again once the task state is set and before the work list is checked, for the rings whose local work this task is the one to run. | |
| Title | io_uring/cancel: rearm local work wake up before sleep | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-11-03T11:20:12.490Z
Reserved: 2026-09-25T10:25:14.403Z
Link: CVE-2026-99253
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
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No weakness.