Bug 2516861 (CVE-2026-74262)

Summary: CVE-2026-74262 kernel: kcm: use WRITE_ONCE() when changing lower socket callbacks
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel's Kernel Connection Multiplexor (KCM) module. This vulnerability occurs due to a race condition when the KCM module replaces or restores lower TCP socket callbacks. If another central processing unit (CPU) observes an outdated callback state, it can lead to mismatched callback execution and incorrect user data. This could result in stale or misdirected wakeups, potentially causing system instability or a denial of service.
 Story Points: ---
Clone Of: Environment:
Last Closed: Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-15 06:37:19 UTC 
In the Linux kernel, the following vulnerability has been resolved:

kcm: use WRITE_ONCE() when changing lower socket callbacks

kcm_attach() replaces a live lower TCP socket's sk_data_ready and
sk_write_space callbacks with KCM handlers, and kcm_unattach() restores
them later. Those callback-pointer updates are still plain stores even
though the same fields can be read and invoked concurrently on other
CPUs.

If another CPU observes an older callback snapshot after the live field
has already been restored, callback execution can run with a mismatched
target and sk_user_data state, leading to stale or misdirected wakeups.

Use WRITE_ONCE() for the callback replacement and restore operations so
these shared callback fields follow the same visibility contract already
established by the earlier 4022 fixes.
Comment 1 gkamathe 2026-08-19 12:52:33 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081542-CVE-2026-74262-7c5b@gregkh/T