Bug 2540472 (CVE-2026-93829)

Summary: CVE-2026-93829 kernel: smb: client: fix races in cifsd thread creation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
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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A flaw was found in the Linux kernel. A race condition exists in the Server Message Block (SMB) client during background worker thread creation, allowing a newly spawned thread to access connection session data before it has been completely initialized. A local user initiating an SMB connection can trigger this timing issue, causing the kernel to hang or crash and resulting in a Denial of Service (DoS).
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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 2026-09-24 16:57:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

smb: client: fix races in cifsd thread creation

The cifsd demultiplex thread can run and access tcp_ses before the parent
thread has finished populating tcp_ses, which the worker thread accesses
locklessly.

Also, the kthread_run macro may start the thread before returning the
thread pointer. Because the pointer is part of the structure that the
thread can access, if the kernel is preempted after the thread is spawned,
but before the thread pointer is populated and the thread attempts to exit,
it will sleep, waiting for a SIGKILL signal.

Fix this by moving creation of the thread to after all of tcp_ses'es
fields are populated, and spawning the thread last, using a split
kthread_create/wake_up_process logic.
Comment 1 Mauro Matteo Cascella 2026-09-28 16:14:01 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93829.mbox