Bug 2393198 (CVE-2025-38704)

Summary: CVE-2025-38704 kernel: rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
Priority: unspecified    
Version: unspecifiedKeywords: Security
Target Milestone: ---   
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
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 2025-09-04 16:04:29 UTC 
In the Linux kernel, the following vulnerability has been resolved:

rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

In the preparation stage of CPU online, if the corresponding
the rdp's->nocb_cb_kthread does not exist, will be created,
there is a situation where the rdp's rcuop kthreads creation fails,
and then de-offload this CPU's rdp, does not assign this CPU's
rdp->nocb_cb_kthread pointer, but this rdp's->nocb_gp_rdp and
rdp's->rdp_gp->nocb_gp_kthread is still valid.

This will cause the subsequent re-offload operation of this offline
CPU, which will pass the conditional check and the kthread_unpark()
will access invalid rdp's->nocb_cb_kthread pointer.

This commit therefore use rdp's->nocb_gp_kthread instead of
rdp_gp's->nocb_gp_kthread for safety check.
Comment 1 Jon Moroney 2025-09-04 17:27:01 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025090454-CVE-2025-38704-4353@gregkh/T