---
id: CVE-2026-89507
title: 'RDMA/ucma: Lock the handler in ucma_write_cm_event()'
summary: |-
  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…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-367
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 <
    4f8bb11dd2ff365e7cff1c9964ab4607292d364e
  - >-
    Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 <
    0be1955040a2eceed0ecfc387fdc92305411d273
  - >-
    Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 <
    f4cc21c6a8e9d392871477f9fd98d68e5ad80272
  - Linux 6.18
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:47:58.674Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89507'
references:
  - url: 'https://git.kernel.org/stable/c/4f8bb11dd2ff365e7cff1c9964ab4607292d364e'
  - url: 'https://git.kernel.org/stable/c/0be1955040a2eceed0ecfc387fdc92305411d273'
  - url: 'https://git.kernel.org/stable/c/f4cc21c6a8e9d392871477f9fd98d68e5ad80272'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89507.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89507'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532319'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89507'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89507'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89507.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00127
epssPercentile: 0.02375
scores:
  cna: 7.8
  vendor: 5.5
ingestedAt: '2026-09-14T15:23:07.475Z'
---

## Overview

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.

## Affected

- `Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 < 4f8bb11dd2ff365e7cff1c9964ab4607292d364e`
- `Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 < 0be1955040a2eceed0ecfc387fdc92305411d273`
- `Linux >= a3c9d0fcd3715541bbf97da2ddde9d032e2fe6d5 < f4cc21c6a8e9d392871477f9fd98d68e5ad80272`
- `Linux 6.18`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat OpenShift Container Platform 4 · updated 2026-09-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89507.json)