# CVE-2026-99125: s390/pai: Handle multiple PMU stop callback invocations


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** BELL-CVE-2026-99125, DEBIAN-CVE-2026-99125, GHSA-83qv-jr76-p4xc, UBUNTU-CVE-2026-99125

## What is CVE-2026-99125?

CVE-2026-99125 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

In the Linux kernel, the following vulnerability has been resolved:

s390/pai: Handle multiple PMU stop callback invocations

Handle the following scenario:
The kernel protects itself against a very high sampling load and
throttles the sampling using:

  perf_event_throttle() --> PMU->stop()

Shortly later the scheduler may terminate the task and removes it from the
CPU. It again calls

  PMU->stop()

which results in two invocations of PMU->stop() called back to back.
Protect against this and check the PERF_HES_STOPPED bit on function
entry.  If it is already set return.
Clear bit PERF_HES_STOPPED in PMU->start().

Prohibit ioctl(fd, PERF_EVENT_IOC_PERIOD, ...) call for this event.
It sets perf_event::event_limit to a positive value and causes
perf_event_overflow() to invoke pai_stop() call back function when
perf_event::event_limit hits zero. This is not supported because the
sample events CRYPTO_ALL and NNPA_ALL are only taken at schedule out
of a task.

Use list_for_each_entry_safe() for safe iteration over syswide_list
in pai_have_samples().

## Which versions are affected by CVE-2026-99125?


## How do I fix CVE-2026-99125?

Upgrade to a fixed version.

## Is CVE-2026-99125 being exploited?

There is no known exploitation of CVE-2026-99125 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99125 and fix it if it is affected.

What it is: CVE-2026-99125 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99125 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-99125/ (Markdown: https://insights.sbomify.com/CVE-2026-99125/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99125
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99125
- OSV: https://osv.dev/vulnerability/CVE-2026-99125

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99125/
Summaries are generated and may contain mistakes; the official description above is the record.