# CVE-2026-89507: RDMA/ucma: Lock the handler in ucma_write_cm_event()


- **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
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-89507, DEBIAN-CVE-2026-89507, GHSA-75mg-q43g-73qj, UBUNTU-CVE-2026-89507

## What is CVE-2026-89507?

CVE-2026-89507 is a high-severity vulnerability in Linux, published on 11 Sep 2026. 

### Official description

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

RDMA/ucma: Lock the handler in ucma_write_cm_event()

ctx->file may only be changed under the handler lock and the xa_lock, which
is what stops uevents being queued for a ctx while ucma_migrate_id() moves
it to another file.  The CM core takes that lock before invoking
ucma_event_handler(), but the write() paths that queue uevents themselves
do not.

ucma_write_cm_event() re-reads ctx->file for each of its four dereferences,
so ucma_migrate_id() can swap it mid-sequence:

	mutex_lock(&ctx->file->mut);			/* file A */
	list_add_tail(&uevent->list, &ctx->file->event_list);	/* file B */
	mutex_unlock(&ctx->file->mut);			/* file B */
	wake_up_interruptible(&ctx->file->poll_wait);	/* file B */

The window is the mutex_lock() itself: the writer sleeps in it while the
migration reassigns ctx->file.  The list_add_tail() then runs on file B's
event_list holding only file A's mutex:

  list_add corruption. prev->next should be next (ffff888101320f30),
    but was ffff88814a08c418. (prev=ffff88814a075c18).
  kernel BUG at lib/list_debug.c:32!
  Call Trace:
   ucma_write_cm_event+0x36e/0x5e0

and file A's mut is left held forever, wedging its next writer in D state.
The uevent is also stranded on a list ucma_cleanup_ctx_events() will not
walk, so it outlives its context.  /dev/infiniband/rdma_cm is 0666 and no
RDMA device is involved, so an unprivileged user reaches all of this.

Take the handler lock, as ucma_cleanup_mc_events() does; ctx->cm_id is
pinned by the ucma_get_ctx() reference.

## Which versions are affected by CVE-2026-89507?


## How do I fix CVE-2026-89507?

Upgrade to a fixed version.

## Is CVE-2026-89507 being exploited?

There is no known exploitation of CVE-2026-89507 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89507 and fix it if it is affected.

What it is: CVE-2026-89507 is a high-severity vulnerability in Linux, published on 11 Sep 2026. 
Exploitation: There is no known exploitation of CVE-2026-89507 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-2026-89507/ (Markdown: https://insights.sbomify.com/CVE-2026-89507/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89507
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89507
- OSV: https://osv.dev/vulnerability/CVE-2026-89507

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89507/
Summaries are generated and may contain mistakes; the official description above is the record.