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 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.