# CVE-2026-98942: sched_ext: Build the cid tables privately and publish them with RCU


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 26 Oct 2026
- **Also known as:** AZL-110735, DEBIAN-CVE-2026-98942, GHSA-rh9v-mpgh-f53x, UBUNTU-CVE-2026-98942

## What is CVE-2026-98942?

CVE-2026-98942 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

sched_ext: Build the cid tables privately and publish them with RCU

The cid tables are visible to the cid kfuncs while being modified: the
first enable publishes the global pointers before filling them,
ops.init_cids() overrides rewrite them in place, and re-enables rebuild
them in place. A racing TRACING or SYSCALL program can read unfilled
entries, including uninitialized memory in the kmalloc'd tables, or torn
topo updates.

Tie the tables' lifetimes to the root sched instead: each root enable
builds a fresh set privately and publishes the per-table __rcu globals once
the layout is final, and root disable unpublishes and RCU-frees the set. A
non-NULL global is now always a fully built table which stays valid for the
reader's RCU read section, and lookups stay two loads. Kfuncs treat NULL as
no-mapping, also after the scheduler exits instead of reporting the stale
last mapping.

The cid kfuncs are available whether the root scheduler is cid-form or
cpu-form, the latter to allow gradual migration to cids. Every root
therefore builds and publishes a default mapping.

Every reader must either be gated on scheduler liveness or NULL-check
inside an RCU read section. Fix the two kfuncs that were neither:
scx_bpf_this_cid() read the table with no RCU or preemption protection and
scx_bpf_task_cid() relied on KF_RCU, which doesn't put a sleepable program
in an RCU read section. The hotplug callbacks are instead serialized by
retiring the tables inside the cpus_read_lock() section that clears
scx_root.

v2: Document why every root builds the tables (desc + cid.c comment).

## Which versions are affected by CVE-2026-98942?


## How do I fix CVE-2026-98942?

Upgrade to a fixed version.

## Is CVE-2026-98942 being exploited?

There is no known exploitation of CVE-2026-98942 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98942 and fix it if it is affected.

What it is: CVE-2026-98942 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-98942 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-2026-98942/ (Markdown: https://insights.sbomify.com/CVE-2026-98942/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98942
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98942
- OSV: https://osv.dev/vulnerability/CVE-2026-98942

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98942/
Summaries are generated and may contain mistakes; the official description above is the record.