CVE-2026-31741

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

counter: rz-mtu3-cnt: prevent counter from being toggled multiple times

Runtime PM counter is incremented / decremented each time the sysfs enable file is written to.

If user writes 0 to the sysfs enable file multiple times, runtime PM usage count underflows, generating the following message.

rz-mtu3-counter rz-mtu3-counter.0: Runtime PM usage count underflow!

At the same time, hardware registers end up being accessed with clocks off in rzmtu3terminate_counter() to disable an already disabled channel.

If user writes 1 to the sysfs enable file multiple times, runtime PM usage count will be incremented each time, requiring the same number of 0 writes to get it back to 0.

If user writes 0 to the sysfs enable file while PWM is in progress, PWM is stopped without counter being the owner of the underlying MTU3 channel.

Check against the cached countisenabled value and exit if the user is trying to set the same enable value.