CVE-2025-38704: rcu/nocb: Fix possible invalid rdp's->nocb_cb_kthread pointer access

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-09-04 · updated 2026-10-19

Description

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.

Affected products

Linux kernel: before 6.12.43; from 6.13 before 6.15.11; from 6.16 before 6.16.2 — fixed in 6.12.43, 6.15.11, 6.16.2

How to fix

Upgrade to a fixed version: Linux kernel 6.12.43, 6.15.11, 6.16.2. Check the vendor advisory for mitigations.

References

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