Bug 2565265 (CVE-2026-99229)

Summary: CVE-2026-99229 kernel: kernel: Denial of Service via stuck io_uring overflow list
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's io_uring subsystem. A local attacker can cause a Denial of Service (DoS) by triggering an infinite loop when waiting for completion queue events. If entries on the overflow list cannot be flushed into the completion queue, the waiting kernel task continuously spins without processing signals or timeouts, resulting in an unkillable process that monopolizes system resources.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description OSIDB Bzimport 2026-11-02 16:42:20 UTC 
In the Linux kernel, the following vulnerability has been resolved:

io_uring/wait: don't spin on a stuck overflow list

As long as IO_CHECK_CQ_OVERFLOW_BIT is set, io_cqring_wait_schedule()
returns right away, before it gets to look at signals or arms the timeout,
for io_cqring_wait() to flush the overflow list. If that doesn't empty the
list, and the CQ ring doesn't hold the number of events the caller wants,
the loop starts over, with the same result. The task spins in the kernel,
and can't be killed.

The assumption is that this can't happen: if CQEs can't be flushed, the
ring is full, and min_events is capped to the size of the ring. But:

- With IORING_SETUP_CQE_MIXED a 32b CQE needs two contiguous entries. It
  is stuck on the list if a single one is free, and then the ring holds
  less than cq_entries events. A single threaded application that asks
  for as many events as the ring has entries never gets out of
  io_uring_enter().

- Whether the ring is full is up to the CQ head, which the application
  can write to. While one thread waits for events on an empty ring,
  another one can move the head back so that the ring looks full and
  have a CQE overflow. The waiter can't be stopped any more, not even by
  SIGKILL.

Only the application can make room in the CQ ring. Return to it if the
list could not be flushed.