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

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.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-89491 being exploited?

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

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-100265, BELL-CVE-2026-89491, DEBIAN-CVE-2026-89491, GHSA-r32m-fj66-qf6p, UBUNTU-CVE-2026-89491.