# CVE-2025-38440: net/mlx5e: Fix race between DIM disable and net_dim()

> A race condition in the Linux kernel mlx5 driver causes a NULL pointer dereference, leading to a system crash.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 25 Jul 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-38440, DEBIAN-CVE-2025-38440, GHSA-4c77-8jrg-w382, ROOT-OS-UBUNTU-2204-CVE-2025-38440, ROOT-OS-UBUNTU-2404-CVE-2025-38440, UBUNTU-CVE-2025-38440

## What is CVE-2025-38440?

CVE-2025-38440 is a high-severity vulnerability in Linux kernel, published on 25 Jul 2025. 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 race between DIM disable and net_dim()

There's a race between disabling DIM and NAPI callbacks using the dim
pointer on the RQ or SQ.

If NAPI checks the DIM state bit and sees it still set, it assumes
`rq->dim` or `sq->dim` is valid. But if DIM gets disabled right after
that check, the pointer might already be set to NULL, leading to a NULL
pointer dereference in net_dim().

Fix this by calling `synchronize_net()` before freeing the DIM context.
This ensures all in-progress NAPI callbacks are finished before the
pointer is cleared.

Kernel log:

BUG: kernel NULL pointer dereference, address: 0000000000000000
...
RIP: 0010:net_dim+0x23/0x190
...
Call Trace:
 <TASK>
 ? __die+0x20/0x60
 ? page_fault_oops+0x150/0x3e0
 ? common_interrupt+0xf/0xa0
 ? sysvec_call_function_single+0xb/0x90
 ? exc_page_fault+0x74/0x130
 ? asm_exc_page_fault+0x22/0x30
 ? net_dim+0x23/0x190
 ? mlx5e_poll_ico_cq+0x41/0x6f0 [mlx5_core]
 ? sysvec_apic_timer_interrupt+0xb/0x90
 mlx5e_handle_rx_dim+0x92/0xd0 [mlx5_core]
 mlx5e_napi_poll+0x2cd/0xac0 [mlx5_core]
 ? mlx5e_poll_ico_cq+0xe5/0x6f0 [mlx5_core]
 busy_poll_stop+0xa2/0x200
 ? mlx5e_napi_poll+0x1d9/0xac0 [mlx5_core]
 ? mlx5e_trigger_irq+0x130/0x130 [mlx5_core]
 __napi_busy_loop+0x345/0x3b0
 ? sysvec_call_function_single+0xb/0x90
 ? asm_sysvec_call_function_single+0x16/0x20
 ? sysvec_apic_timer_interrupt+0xb/0x90
 ? pcpu_free_area+0x1e4/0x2e0
 napi_busy_loop+0x11/0x20
 xsk_recvmsg+0x10c/0x130
 sock_recvmsg+0x44/0x70
 __sys_recvfrom+0xbc/0x130
 ? __schedule+0x398/0x890
 __x64_sys_recvfrom+0x20/0x30
 do_syscall_64+0x4c/0x100
 entry_SYSCALL_64_after_hwframe+0x4b/0x53
...
---[ end trace 0000000000000000 ]---
...
---[ end Kernel panic - not syncing: Fatal exception in interrupt ]---

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2025-38440?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38440?

Apply the vendor's patch.

## Is CVE-2025-38440 being exploited?

There is no known exploitation of CVE-2025-38440 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-38440 and fix it if it is affected.

What it is: CVE-2025-38440 is a high-severity vulnerability in Linux kernel, published on 25 Jul 2025. 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-2025-38440 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2025-38440/ (Markdown: https://insights.sbomify.com/CVE-2025-38440/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38440
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38440
- OSV: https://osv.dev/vulnerability/CVE-2025-38440

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38440/
Summaries are generated and may contain mistakes; the official description above is the record.