CVE-2025-38632: pinmux: fix race causing mux_owner NULL with active mux_usecount
In the Linux kernel, the following vulnerability has been resolved:
pinmux: fix race causing muxowner NULL with active muxusecount
commit 5a3e85c3c397 ("pinmux: Use sequential access to access desc->pinmux data") tried to address the issue when two client of the same gpio calls pinctrlselectstate() for the same functionality, was resulting in NULL pointer issue while accessing desc->muxowner. However, issue was not completely fixed due to the way it was handled and it can still result in the same NULL pointer.
The issue occurs due to the following interleaving:
cpu0 (process A) cpu1 (process B)
pinrequest() { pinfree() {
mutexlock() desc->muxusecount--; //becomes 0 .. mutexunlock()
mutexlock(desc->mux) desc->muxusecount++; // becomes 1 desc->muxowner = owner; mutexunlock(desc->mux)
mutexlock(desc->mux) desc->muxowner = NULL; mutexunlock(desc->mux)
This sequence leads to a state where the pin appears to be in use (muxusecount == 1) but has no owner (muxowner == NULL), which can cause NULL pointer on next pinrequest on the same pin.
Ensure that updates to muxusecount and muxowner are performed atomically under the same lock. Only clear muxowner when muxusecount reaches zero and no new owner has been assigned.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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debian/linuxto a version that resolves this vulnerability.Fixed in 6.12.43-1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1047.50+fips1 - Configuration
Modify pinmux handling so updates to mux_usecount and mux_owner occur atomically under the same mutex, and mux_owner is cleared only when mux_usecount reaches zero with no new owner assigned.
Linux kernel pinmux mux_usecount and mux_owner update synchronization = Atomically update both under the same lock; clear mux_owner only when mux_usecount reaches zero and no new owner has been assigned
Event History
Frequently Asked Questions
What is the severity of CVE-2025-38632?
CVE-2025-38632 has been classified as having a high severity level due to the potential risk of race conditions affecting GPIO operations in the Linux kernel.
How do I fix CVE-2025-38632?
To fix CVE-2025-38632, upgrade to the latest version of the Linux kernel that includes the patch addressing this vulnerability.
What is the impact of CVE-2025-38632?
The impact of CVE-2025-38632 may lead to system instability or unintended behavior due to incorrect access to pin multiplexing controls.
Which versions of Linux kernel are affected by CVE-2025-38632?
CVE-2025-38632 affects certain versions of the Linux kernel where the pin multiplexing functionality is implemented.
Is there a workaround for CVE-2025-38632?
Currently, the recommended approach for CVE-2025-38632 is to apply the official patches rather than relying on workarounds.