# CVE-2025-40134: dm: fix NULL pointer dereference in __dm_suspend()

> A race condition in the Linux kernel device-mapper subsystem allows a local attacker to cause a denial of service via a NULL pointer dereference.

- **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:** 12 Nov 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40134, DEBIAN-CVE-2025-40134, GHSA-m29g-8vpf-pc8m, ROOT-OS-DEBIAN-11-CVE-2025-40134, ROOT-OS-DEBIAN-13-CVE-2025-40134, ROOT-OS-UBUNTU-2404-CVE-2025-40134, UBUNTU-CVE-2025-40134

## What is CVE-2025-40134?

CVE-2025-40134 is a vulnerability in Linux, published on 12 Nov 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:

dm: fix NULL pointer dereference in __dm_suspend()

There is a race condition between dm device suspend and table load that
can lead to null pointer dereference. The issue occurs when suspend is
invoked before table load completes:

BUG: kernel NULL pointer dereference, address: 0000000000000054
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 6 PID: 6798 Comm: dmsetup Not tainted 6.6.0-g7e52f5f0ca9b #62
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014
RIP: 0010:blk_mq_wait_quiesce_done+0x0/0x50
Call Trace:
  <TASK>
  blk_mq_quiesce_queue+0x2c/0x50
  dm_stop_queue+0xd/0x20
  __dm_suspend+0x130/0x330
  dm_suspend+0x11a/0x180
  dev_suspend+0x27e/0x560
  ctl_ioctl+0x4cf/0x850
  dm_ctl_ioctl+0xd/0x20
  vfs_ioctl+0x1d/0x50
  __se_sys_ioctl+0x9b/0xc0
  __x64_sys_ioctl+0x19/0x30
  x64_sys_call+0x2c4a/0x4620
  do_syscall_64+0x9e/0x1b0

The issue can be triggered as below:

T1 						T2
dm_suspend					table_load
__dm_suspend					dm_setup_md_queue
						dm_mq_init_request_queue
						blk_mq_init_allocated_queue
						=> q->mq_ops = set->ops; (1)
dm_stop_queue / dm_wait_for_completion
=> q->tag_set NULL pointer!	(2)
						=> q->tag_set = set; (3)

Fix this by checking if a valid table (map) exists before performing
request-based suspend and waiting for target I/O. When map is NULL,
skip these table-dependent suspend steps.

Even when map is NULL, no I/O can reach any target because there is
no table loaded; I/O submitted in this state will fail early in the
DM layer. Skipping the table-dependent suspend logic in this case
is safe and avoids NULL pointer dereferences.

## Which versions are affected by CVE-2025-40134?


## How do I fix CVE-2025-40134?

Apply the vendor's patch.

## Is CVE-2025-40134 being exploited?

There is no known exploitation of CVE-2025-40134 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40134 and fix it if it is affected.

What it is: CVE-2025-40134 is a vulnerability in Linux, published on 12 Nov 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-2025-40134 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-2025-40134/ (Markdown: https://insights.sbomify.com/CVE-2025-40134/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40134
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40134
- OSV: https://osv.dev/vulnerability/CVE-2025-40134

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40134/
Summaries are generated and may contain mistakes; the official description above is the record.