CVE-2025-38632

In the Linux kernel, the following vulnerability has been resolved:

pinmux: fix race causing muxowner NULL with active muxusecount

commit 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") tried to address the issue when two client of the same gpio calls pinctrlselectstate() 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()

mutexlock(desc->mux) desc->muxusecount++; // becomes 1 desc->muxowner = owner; mutexunlock(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 muxusecount and muxowner are performed atomically under the same lock. Only clear muxowner when muxusecount reaches zero and no new owner has been assigned.