CVE-2026-99227
io_uring/waitid: prevent cancel reference wrap
What happened?
In the Linux kernel, the following vulnerability has been resolved:
io_uring/waitid: prevent cancel reference wrap
io_waitid packs the cancellation state into bit 31 of ->refs and uses bits 30:0 as a 31-bit reference counter:
#define IO_WAITID_CANCEL_FLAG BIT(31) #define IO_WAITID_REF_MASK GENMASK(30, 0)
__io_waitid_cancel() marks a request canceled, then increments the low bits of ->refs to claim completion ownership. When another path owns the request, the increment remains even though cancellation returns false. The request remains discoverable by cancellation, so repeated failed attempts can wrap the 31-bit reference field to zero. A later cancellation can claim ownership and complete the request a second time.
Use atomic_fetch_or() when setting the cancel flag and inspect the old flag value. The first cancel attempt continues to the existing ownership increment, preserving its wake and issuer handoff semantics. Later attempts see the cancel flag and return without incrementing the reference field.
This makes repeated failed cancellation attempts idempotent while leaving the first-cancel state transitions unchanged.
Affected software and versions
| Software | Version information | Fixed version |
|---|---|---|
| LinuxLinux | affected: f31ecf671ddc498f20219453395794ff2383e06b to < 20b67288574c7c3df6b8ea7ed3b7af90a868006f; affected: f31ecf671ddc498f20219453395794ff2383e06b to < 5bfeee1774791602a0d53eb717f00f172127a017; affected: f31ecf671ddc498f20219453395794ff2383e06b to < 857aa2012b91cad6fdef54a4b6c632d9d0b6e64f; affected: f31ecf671ddc498f20219453395794ff2383e06b to < 22fb4a4518e305164c7f203608287564de292f34; affected: f31ecf671ddc498f20219453395794ff2383e06b to < 98787d3fa4e99564d2b2bc21255b21f670c450d0 | See vendor advisory |
| LinuxLinux | affected: 6.7; unaffected: 0 to < 6.7; unaffected: 6.12.115 to ≤ 6.12.*; unaffected: 6.18.60 to ≤ 6.18.*; unaffected: 7.2.14 to ≤ 7.2.*; unaffected: 7.3.1 to ≤ 7.3.*; unaffected: 7.4-rc1 to ≤ * | See vendor advisory |
Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.
Is it being exploited?
This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.
How to respond
- Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
- Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
- Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.
Sources and remediation references
- https://www.cve.org/CVERecord?id=CVE-2026-99227
- https://git.kernel.org/stable/c/20b67288574c7c3df6b8ea7ed3b7af90a868006f
- https://git.kernel.org/stable/c/5bfeee1774791602a0d53eb717f00f172127a017
- https://git.kernel.org/stable/c/857aa2012b91cad6fdef54a4b6c632d9d0b6e64f
- https://git.kernel.org/stable/c/22fb4a4518e305164c7f203608287564de292f34
- https://git.kernel.org/stable/c/98787d3fa4e99564d2b2bc21255b21f670c450d0