# CVE-2026-72342: net/mlx5e: Fix HV VHCA stats agent registration race

> A race condition in the Linux kernel mlx5e driver can cause a null pointer dereference or timer corruption, leading to a system crash.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** BELL-CVE-2026-72342, DEBIAN-CVE-2026-72342, GHSA-q42x-cp58-jpg7, UBUNTU-CVE-2026-72342

## What is CVE-2026-72342?

CVE-2026-72342 is a high-severity vulnerability in Linux, published on 15 Aug 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:

net/mlx5e: Fix HV VHCA stats agent registration race

mlx5e_hv_vhca_stats_create() registers the stats agent through
mlx5_hv_vhca_agent_create(). The helper publishes the agent in
hv_vhca->agents[type] under agents_lock and immediately schedules an
asynchronous control invalidation on the HV VHCA workqueue before
returning to mlx5e.

The asynchronous invalidation invokes the control agent's invalidate
callback, which reads the hypervisor control block and forwards the
command to mlx5e_hv_vhca_stats_control(). That callback may either:

  - call cancel_delayed_work_sync(&priv->stats_agent.work), or
  - call queue_delayed_work(priv->wq, &sagent->work, sagent->delay).

However, the delayed_work and priv->stats_agent.agent are only
initialized after mlx5_hv_vhca_agent_create() returns to mlx5e:

    agent = mlx5_hv_vhca_agent_create(...);   /* publish + invalidate */
    ...
    priv->stats_agent.agent = agent;          /* too late */
    INIT_DELAYED_WORK(&priv->stats_agent.work, ...); /* too late */

If the asynchronous control path runs before the two assignments
above, it can:

  - Operate on an uninitialized delayed_work whose timer.function is
    NULL. queue_delayed_work() calls add_timer() unconditionally, so
    when the timer expires the timer softirq invokes a NULL function
    pointer.
  - Re-initialize the timer later through INIT_DELAYED_WORK() while
    the timer is already enqueued in the timer wheel, corrupting the
    hlist (entry.pprev cleared while the previous bucket node still
    points at this entry).
  - When the worker eventually runs, mlx5e_hv_vhca_stats_work() reads
    sagent->agent (NULL) and dereferences it inside
    mlx5_hv_vhca_agent_write().

Fix this by:

  - Initializing priv->stats_agent.work before invoking
    mlx5_hv_vhca_agent_create(), so the work is always in a valid
    state when the control callback observes it.
  - Adding a struct mlx5_hv_vhca_agent **ctx_update out-parameter
    to mlx5_hv_vhca_agent_create(). The helper writes the agent
    pointer to *ctx_update before publishing into hv_vhca->agents[]
    and triggering the agents_update flow, so any callback
    subsequently invoked from that flow already sees a valid
    priv->stats_agent.agent. This avoids having the control
    callback participate in agent initialization.

While at it, access priv->stats_agent.agent with
READ_ONCE()/WRITE_ONCE() for the cross-CPU access with the worker, and
clear priv->stats_agent.buf on the agent_create() failure path.

## Which versions are affected by CVE-2026-72342?


## How do I fix CVE-2026-72342?

Apply the vendor's patch.

## Is CVE-2026-72342 being exploited?

There is no known exploitation of CVE-2026-72342 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72342 and fix it if it is affected.

What it is: CVE-2026-72342 is a high-severity vulnerability in Linux, published on 15 Aug 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-2026-72342 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-2026-72342/ (Markdown: https://insights.sbomify.com/CVE-2026-72342/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72342
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72342
- OSV: https://osv.dev/vulnerability/CVE-2026-72342

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72342/
Summaries are generated and may contain mistakes; the official description above is the record.