CVE-2025-38632: pinmux: fix race causing mux_owner NULL with active mux_usecount

Severity: medium (CVSS 4.7 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-08-22 · updated 2026-10-30
Weakness: CWE-362

Description

In the Linux kernel, the following vulnerability has been resolved: pinmux: fix race causing mux_owner NULL with active mux_usecount commit 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") tried to address the issue when two client of the same gpio calls pinctrl_select_state() for the same functionality, was resulting in NULL pointer issue while accessing desc->mux_owner. However, issue was not completely fixed due to the way it was handled and it can still result in the same NULL pointer. The issue occurs due to the following interleaving: cpu0 (process A) cpu1 (process B) pin_request() { pin_free() { mutex_lock() desc->mux_usecount--; //becomes 0 .. mutex_unlock() mutex_lock(desc->mux) desc->mux_usecount++; // becomes 1 desc->mux_owner = owner; mutex_unlock(desc->mux) mutex_lock(desc->mux) desc->mux_owner = NULL; mutex_unlock(desc->mux) This sequence leads to a state where the pin appears to be in use (`mux_usecount == 1`) but has no owner (`mux_owner == NULL`), which can cause NULL pointer on next pin_request on the same pin. Ensure that updates to mux_usecount and mux_owner are performed atomically under the same lock. Only clear mux_owner when mux_usecount reaches zero and no new owner has been assigned.

Affected products

Linux kernel: from 6.6.66 before 6.6.102; from 6.12.5 before 6.12.42; from 6.13 before 6.15.10; from 6.16 before 6.16.1 — fixed in 6.6.102, 6.12.42, 6.15.10, 6.16.1
Linux: from 6.6.66 before 6.6.102; from 6.12.5 before 6.12.42 — fixed in 6.6.102, 6.12.42

How to fix

Upgrade to a fixed version: Linux kernel 6.6.102, 6.12.42, 6.15.10, 6.16.1; Linux 6.6.102, 6.12.42. Check the vendor advisory for mitigations.

References

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