Bug 2297504 (CVE-2024-40920)

Summary: CVE-2024-40920 kernel: net: bridge: mst: fix suspicious rcu usage in br_mst_set_state
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: dfreiber, drow, jburrell, vkumar
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: kernel 6.1.95, kernel 6.6.35, kernel 6.9.6, kernel 6.10-rc4 Doc Type: If docs needed, set a value
Doc Text:
A vulnerability was found in the Linux kernel's bridge subsystem, related to Multiple Spanning Tree (MST). The `br_mst_set_state` function was converted to use RCU to prevent a VLAN use-after-free, but fails to update the VLAN group dereference helper. This leads to warnings about improper RCU usage.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2024-07-12 13:32:22 UTC 
In the Linux kernel, the following vulnerability has been resolved:

net: bridge: mst: fix suspicious rcu usage in br_mst_set_state

I converted br_mst_set_state to RCU to avoid a vlan use-after-free
but forgot to change the vlan group dereference helper. Switch to vlan
group RCU deref helper to fix the suspicious rcu usage warning.