Bug 2464355 (CVE-2026-31740)

Summary: CVE-2026-31740 kernel: counter: rz-mtu3-cnt: do not use struct rz_mtu3_channel's dev member
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: unspecified Docs Contact:
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 driver. A race condition exists where multiple sub-drivers can simultaneously attempt to assign their device pointers to a shared channel member. This can result in the counter sub-driver performing power management actions on an unintended device, potentially leading to system instability or unexpected operational behavior.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Description OSIDB Bzimport 2026-05-01 15:01:57 UTC 
In the Linux kernel, the following vulnerability has been resolved:

counter: rz-mtu3-cnt: do not use struct rz_mtu3_channel's dev member

The counter driver can use HW channels 1 and 2, while the PWM driver can
use HW channels 0, 1, 2, 3, 4, 6, 7.

The dev member is assigned both by the counter driver and the PWM driver
for channels 1 and 2, to their own struct device instance, overwriting
the previous value.

The sub-drivers race to assign their own struct device pointer to the
same struct rz_mtu3_channel's dev member.

The dev member of struct rz_mtu3_channel is used by the counter
sub-driver for runtime PM.

Depending on the probe order of the counter and PWM sub-drivers, the
dev member may point to the wrong struct device instance, causing the
counter sub-driver to do runtime PM actions on the wrong device.

To fix this, use the parent pointer of the counter, which is assigned
during probe to the correct struct device, not the struct device pointer
inside the shared struct rz_mtu3_channel.
Comment 1 Keith Grant 2026-05-01 21:40:01 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050139-CVE-2026-31740-70c8@gregkh/T