# CVE-2026-90342: bpf: Fix mmap_lock deadlock on arena lock failure

> A local attacker can trigger a kernel deadlock in the BPF arena fault handler, causing a system-wide denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-90342, GHSA-xw74-j5c3-43ch, UBUNTU-CVE-2026-90342

## What is CVE-2026-90342?

CVE-2026-90342 is a denial of service vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

bpf: Fix mmap_lock deadlock on arena lock failure

Reported by the Sashiko AI review.

arena_vm_fault() returns VM_FAULT_RETRY when it can't take
arena->spinlock, but it never took mmap_lock. The fault path assumes a
VM_FAULT_RETRY handler already dropped mmap_lock and re-takes it on the
retry, so mmap_lock gets taken twice and can deadlock:

	do_user_addr_fault()
	{
		fault = handle_mm_fault(...);   // calls arena_vm_fault()
		if (fault & VM_FAULT_RETRY)
			goto retry;   // re-locks mmap_lock
		mmap_read_unlock(mm);
	}

Return VM_FAULT_SIGBUS instead, for two reasons:

1. We could keep VM_FAULT_RETRY, but then we'd have to drop the fault
   lock first and cap the retry ourselves, the way __folio_lock_or_retry()
   does.

2. A failed raw_res_spin_lock_irqsave() already means a possible deadlock
   was detected, so retrying just hits the same lock again.

So returning VM_FAULT_RETRY here is overkill.

## Which versions are affected by CVE-2026-90342?


## How do I fix CVE-2026-90342?

Apply the vendor's patch.

## Is CVE-2026-90342 being exploited?

There is no known exploitation of CVE-2026-90342 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90342 and fix it if it is affected.

What it is: CVE-2026-90342 is a denial of service vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-90342 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-2026-90342/ (Markdown: https://insights.sbomify.com/CVE-2026-90342/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90342
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90342
- OSV: https://osv.dev/vulnerability/CVE-2026-90342

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90342/
Summaries are generated and may contain mistakes; the official description above is the record.