# CVE-2025-40251: devlink: rate: Unset parent pointer in devl_rate_nodes_destroy

> A missing pointer cleanup in the Linux kernel devlink rate subsystem causes a dangling pointer, leading to refcount errors and potential system crashes.

- **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:** 4 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-71420, AZL-78395, BELL-CVE-2025-40251, DEBIAN-CVE-2025-40251, GHSA-4fxr-v6jm-9j9m, ROOT-OS-DEBIAN-12-CVE-2025-40251, ROOT-OS-DEBIAN-13-CVE-2025-40251, ROOT-OS-UBUNTU-2204-CVE-2025-40251, ROOT-OS-UBUNTU-2404-CVE-2025-40251, UBUNTU-CVE-2025-40251

## What is CVE-2025-40251?

CVE-2025-40251 is a high-severity vulnerability in Linux kernel, published on 4 Dec 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:

devlink: rate: Unset parent pointer in devl_rate_nodes_destroy

The function devl_rate_nodes_destroy is documented to "Unset parent for
all rate objects". However, it was only calling the driver-specific
`rate_leaf_parent_set` or `rate_node_parent_set` ops and decrementing
the parent's refcount, without actually setting the
`devlink_rate->parent` pointer to NULL.

This leaves a dangling pointer in the `devlink_rate` struct, which cause
refcount error in netdevsim[1] and mlx5[2]. In addition, this is
inconsistent with the behavior of `devlink_nl_rate_parent_node_set`,
where the parent pointer is correctly cleared.

This patch fixes the issue by explicitly setting `devlink_rate->parent`
to NULL after notifying the driver, thus fulfilling the function's
documented behavior for all rate objects.

[1]
repro steps:
echo 1 > /sys/bus/netdevsim/new_device
devlink dev eswitch set netdevsim/netdevsim1 mode switchdev
echo 1 > /sys/bus/netdevsim/devices/netdevsim1/sriov_numvfs
devlink port function rate add netdevsim/netdevsim1/test_node
devlink port function rate set netdevsim/netdevsim1/128 parent test_node
echo 1 > /sys/bus/netdevsim/del_device

dmesg:
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 8 PID: 1530 at lib/refcount.c:31 refcount_warn_saturate+0x42/0xe0
CPU: 8 UID: 0 PID: 1530 Comm: bash Not tainted 6.18.0-rc4+ #1 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
RIP: 0010:refcount_warn_saturate+0x42/0xe0
Call Trace:
 <TASK>
 devl_rate_leaf_destroy+0x8d/0x90
 __nsim_dev_port_del+0x6c/0x70 [netdevsim]
 nsim_dev_reload_destroy+0x11c/0x140 [netdevsim]
 nsim_drv_remove+0x2b/0xb0 [netdevsim]
 device_release_driver_internal+0x194/0x1f0
 bus_remove_device+0xc6/0x130
 device_del+0x159/0x3c0
 device_unregister+0x1a/0x60
 del_device_store+0x111/0x170 [netdevsim]
 kernfs_fop_write_iter+0x12e/0x1e0
 vfs_write+0x215/0x3d0
 ksys_write+0x5f/0xd0
 do_syscall_64+0x55/0x10f0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

[2]
devlink dev eswitch set pci/0000:08:00.0 mode switchdev
devlink port add pci/0000:08:00.0 flavour pcisf pfnum 0 sfnum 1000
devlink port function rate add pci/0000:08:00.0/group1
devlink port function rate set pci/0000:08:00.0/32768 parent group1
modprobe -r mlx5_ib mlx5_fwctl mlx5_core

dmesg:
refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 7 PID: 16151 at lib/refcount.c:31 refcount_warn_saturate+0x42/0xe0
CPU: 7 UID: 0 PID: 16151 Comm: bash Not tainted 6.17.0-rc7_for_upstream_min_debug_2025_10_02_12_44 #1 NONE
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:refcount_warn_saturate+0x42/0xe0
Call Trace:
 <TASK>
 devl_rate_leaf_destroy+0x8d/0x90
 mlx5_esw_offloads_devlink_port_unregister+0x33/0x60 [mlx5_core]
 mlx5_esw_offloads_unload_rep+0x3f/0x50 [mlx5_core]
 mlx5_eswitch_unload_sf_vport+0x40/0x90 [mlx5_core]
 mlx5_sf_esw_event+0xc4/0x120 [mlx5_core]
 notifier_call_chain+0x33/0xa0
 blocking_notifier_call_chain+0x3b/0x50
 mlx5_eswitch_disable_locked+0x50/0x110 [mlx5_core]
 mlx5_eswitch_disable+0x63/0x90 [mlx5_core]
 mlx5_unload+0x1d/0x170 [mlx5_core]
 mlx5_uninit_one+0xa2/0x130 [mlx5_core]
 remove_one+0x78/0xd0 [mlx5_core]
 pci_device_remove+0x39/0xa0
 device_release_driver_internal+0x194/0x1f0
 unbind_store+0x99/0xa0
 kernfs_fop_write_iter+0x12e/0x1e0
 vfs_write+0x215/0x3d0
 ksys_write+0x5f/0xd0
 do_syscall_64+0x53/0x1f0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-40251?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-40251?

Apply the vendor's patch.

## Is CVE-2025-40251 being exploited?

There is no known exploitation of CVE-2025-40251 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-2025-40251 and fix it if it is affected.

What it is: CVE-2025-40251 is a high-severity vulnerability in Linux kernel, published on 4 Dec 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-2025-40251 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-2025-40251/ (Markdown: https://insights.sbomify.com/CVE-2025-40251/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40251
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40251
- OSV: https://osv.dev/vulnerability/CVE-2025-40251

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40251/
Summaries are generated and may contain mistakes; the official description above is the record.