Linux Kernel io_uring: Overflow List Spinlock DoS
CVE-2026-99229 Published on November 2, 2026
io_uring/wait: don't spin on a stuck overflow list
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.
Products Associated with CVE-2026-99229
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Affected Versions
Linux:- Version 3fcf19d592d5cb63eb209400b22055651e3c27d0 and below bf1d2ed84b3162e3b0e0bb7018ac59147da6e975 is affected.
- Version 3fcf19d592d5cb63eb209400b22055651e3c27d0 and below a6cfc85c6bf9498aaf1978b503f9663635a1aa22 is affected.
- Version 3fcf19d592d5cb63eb209400b22055651e3c27d0 and below 4a89352edd8b3e20d1e1fb33f0fc297dd137149f is affected.
- Version 3fcf19d592d5cb63eb209400b22055651e3c27d0 and below c347691e5dc5481b2d6943c123619e04847fb0dc is affected.
- Version 6.3 is affected.
- Before 6.3 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.