# CVE-2026-89491: ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()

> A local attacker can trigger a kernel bug or deadlock in the OCFS2 cluster module by mounting a filesystem, causing a denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **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-100265, BELL-CVE-2026-89491, DEBIAN-CVE-2026-89491, GHSA-r32m-fj66-qf6p, UBUNTU-CVE-2026-89491

## What is CVE-2026-89491?

CVE-2026-89491 is a denial of service 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:

ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()

Patch series "ocfs2: cluster: o2hb_region_pin() fixes", v2.

This series fixes three related issues in o2hb_region_pin(), all are from
the original implementation in commit: 58a3158a5d17 ("ocfs2/cluster:
Pin/unpin o2hb regions"):

1) It is called with o2hb_live_lock (a spinlock) held, but the
   underlying configfs_depend_item() sleeps (takes inode rwsem and
   pins the filesystem).  This triggers BUG under
   CONFIG_DEBUG_ATOMIC_SLEEP.

2) When called from the configfs drop_item callback, it creates a
   lock order inversion: parent inode_lock -> configfs root
   inode_lock, which can deadlock against subsystem unregistration
   paths taking root -> parent.

3) If pinning fails partway through o2hb_region_inc_user(), the
   o2hb_dependent_users counter is leaked and partially-pinned
   regions are never released, leaving heartbeat regions
   unprotected on subsequent mounts.

Patch 1 reworks o2hb_region_pin() to drop o2hb_live_lock across each
sleeping configfs_depend_item() call, using a config_item reference to
keep the region alive while unlocked.

Patch 2 adds a from_callback parameter to select
configfs_depend_item_unlocked() when called from configfs context,
avoiding the inode_lock nesting.

Patch 3 fixes the error path in o2hb_region_inc_user() to unpin and
decrement the counter on failure.

This patch (of 3):

o2hb_region_pin() is always called with the o2hb_live_lock spinlock held
(from o2hb_region_inc_user() and o2hb_heartbeat_group_drop_item()), but it
calls o2nm_depend_item() -> configfs_depend_item(), which sleeps: it pins
the configfs filesystem and takes the configfs root inode rwsem.  Under
CONFIG_DEBUG_ATOMIC_SLEEP this triggers:

  BUG: sleeping function called from invalid context at kernel/locking/rwsem.c
  in_atomic(): 1, ... name: mount.ocfs2
    down_write
    configfs_depend_item
    o2hb_region_pin
    o2hb_region_inc_user
    o2hb_register_callback
    dlm_register_domain_handlers
    ...
    ocfs2_dlm_init
    ocfs2_mount_volume
    ocfs2_fill_super

Rework o2hb_region_pin() to pin one region at a time with the lock dropped
across the sleeping call: under o2hb_live_lock find the next eligible
region and take a config_item reference to keep it alive, drop the lock,
call o2nm_depend_item(), then retake the lock and record the pin.  The
config_item_put() is done with the lock released as well, since
o2hb_region_release() also acquires o2hb_live_lock and can sleep.  The
region list may change while unlocked, so the scan restarts from the top
after each pin.  Local heartbeat still pins only the matching region;
global heartbeat pins all eligible regions.

The unpin path is unaffected: configfs_undepend_item() only takes a
spinlock and does not sleep.

## Which versions are affected by CVE-2026-89491?


## How do I fix CVE-2026-89491?

Apply the vendor's patch.

## Is CVE-2026-89491 being exploited?

There is no known exploitation of CVE-2026-89491 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89491 and fix it if it is affected.

What it is: CVE-2026-89491 is a denial of service 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-2026-89491 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-2026-89491/ (Markdown: https://insights.sbomify.com/CVE-2026-89491/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89491
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89491
- OSV: https://osv.dev/vulnerability/CVE-2026-89491

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89491/
Summaries are generated and may contain mistakes; the official description above is the record.