CVE-2025-38632

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.

A race between pin_request() and pin_free() could leave a pinmux descriptor with mux_usecount == 1 but mux_owner == NULL, leading to a NULL-pointer dereference on subsequent requests. The fix makes updates to mux_usecount and mux_owner atomic under the same lock and only clears the owner when the count drops to zero. Practically, exploitation requires local access to pin control/GPIO operations (e.g., competing clients of the same pin), so this is a local reliability/DoS issue rather than a data-confidentiality or integrity risk. Typically needs high privileges (root/CAPs or device-node access).

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.