# CVE-2026-89508: RDMA/ucma: Lock the handler in ucma_set_ib_path()

> A race condition in the Linux kernel RDMA subsystem allows a use-after-free, potentially leading to denial of service or code execution.

- **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:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100088, BELL-CVE-2026-89508, DEBIAN-CVE-2026-89508, GHSA-r924-qj9j-26c5, UBUNTU-CVE-2026-89508

## What is CVE-2026-89508?

CVE-2026-89508 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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:

RDMA/ucma: Lock the handler in ucma_set_ib_path()

ucma_set_ib_path() calls ucma_event_handler() straight from the write()
path, without the handler lock that keeps ctx->file stable while a uevent
is queued.  The handler re-reads ctx->file for every dereference:

	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 */

A concurrent ucma_migrate_id() reassigns ctx->file while the SET_OPTION
caller sleeps in mutex_lock(), so the list_add_tail() lands on file B's
event_list while only file A's mutex is held, racing every other user of
that list:

  BUG: KASAN: slab-use-after-free in __list_add_valid_or_report+0x1aa/0x1c0
  Read of size 8 at addr ffff888153c6a418 by task poc_corr/486
  Call Trace:
   __list_add_valid_or_report+0x1aa/0x1c0
   ucma_event_handler+0x1be/0xc00
   ucma_set_ib_path+0x45e/0x710
   ucma_set_option+0x32e/0x590
   ucma_write+0x1f9/0x330
  Allocated by task 505:
   ucma_write_cm_event+0x1a1/0x660
  Freed by task 505:
   kfree+0x1da/0x4c0
   ucma_get_event+0x5d5/0x7e0

The freed object is a ucma_event that another thread dequeued from file B's
list under file B's mutex.  File A's mut is left held on top of that,
wedging its next writer in uninterruptible sleep.

This path needs a bound and address-resolved cm_id, so it requires an RDMA
device to be present.

Take the handler lock around the call.

## Which versions are affected by CVE-2026-89508?


## How do I fix CVE-2026-89508?

Apply the vendor's patch.

## Is CVE-2026-89508 being exploited?

There is no known exploitation of CVE-2026-89508 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89508 and fix it if it is affected.

What it is: CVE-2026-89508 is a high-severity use after free vulnerability in Linux, published on 11 Sep 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-2026-89508 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-2026-89508/ (Markdown: https://insights.sbomify.com/CVE-2026-89508/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89508
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89508
- OSV: https://osv.dev/vulnerability/CVE-2026-89508

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89508/
Summaries are generated and may contain mistakes; the official description above is the record.