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 rz_mtu3_terminate_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 count_is_enabled value and exit if the user is trying to set the same enable value.