Bug 2464501 (CVE-2026-31741)

Summary: CVE-2026-31741 kernel: counter: rz-mtu3-cnt: prevent counter from being toggled multiple times
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: unspecified    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Doc Text:
A flaw was found in the Linux kernel's `rz-mtu3-cnt` counter module. A local user can exploit this by repeatedly writing '0' to the sysfs enable file, which causes the runtime Power Management (PM) usage count to underflow. This can lead to attempts to access hardware registers with their clocks off, potentially causing system instability or a denial of service (DoS). Additionally, repeated writes of '1' can cause the usage count to increment indefinitely, requiring an equal number of '0' writes to reset it.
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Description OSIDB Bzimport 2026-05-01 15:10:17 UTC 
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.
Comment 1 Keith Grant 2026-05-01 21:42:17 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050139-CVE-2026-31741-08c6@gregkh/T