CVE-2026-89495: ocfs2: bound namelen in dlm_migrate_request_handler

CVE-2026-89495: ocfs2: bound namelen in dlm_migrate_request_handler

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

ocfs2: bound namelen in dlm_migrate_request_handler

Patch series "ocfs2/dlm: bound peer-controlled lengths in the o2dlm".

The o2dlm receive handlers trust u8 length and count fields from the wire
without bounding them, so a node in a DLM domain can corrupt or panic any
other node with a malformed message.  Three defects:

  - dlm_migrate_request_handler() passes migrate->namelen unchecked to
    dlm_init_mle(), which memcpy()s it into the 32-byte mname[] of an
    o2dlm_mle slab object: a heap out-of-bounds write of up to ~215
    attacker-controlled bytes.

  - dlm_mig_lockres_handler() passes mres->lockname_len unchecked to
    dlm_init_lockres(), which memcpy()s it into the 32-byte o2dlm_lockname
    slab object: a heap out-of-bounds write of up to ~223 bytes.

  - the same handler trusts mres->num_locks without checking that the
    message is large enough to hold that many entries, so
    dlm_process_recovery_data() walks mres->ml[] past the kmalloc(data_len)
    copy and trips a BUG_ON (an out-of-bounds read ending in a panic).

The other o2dlm receive handlers already reject an oversized name; the
migration and recovery handlers have omitted it since the DLM was added
(see the Fixes tags).  Patch 1 bounds namelen; patch 2 validates
lockname_len, num_locks, and the payload size.  Conforming recovery and
migration traffic is unaffected.

o2net authenticates peers only by the DLM domain key, so any node that has
joined the domain -- including a compromised or malicious member -- can
send these messages.  There is no local trigger; the attacker must already
be a member of the cluster.

Each sink was confirmed under KASAN with an out-of-tree module mirroring
it exactly -- a kmem_cache/kmalloc of the real destination size, then the
same unclamped memcpy/loop: slab-out-of-bounds Write for the two writes,
Read for the recovery walk, and a panic.  A userspace AddressSanitizer
build faults identically under -m32 and -m64.  Scrubbed logs are available
on request.

I reported this privately to security@kernel.org and the ocfs2 maintainers
on 2026-06-20; with no response after the standard embargo period I am
posting the fix publicly.  I have no embargo requirement.


This patch (of 2):

A node receiving a DLM_MIGRATE_REQUEST message trusts the peer-supplied
name length (migrate->namelen) without bounding it.  dlm_init_mle() then
copies that many bytes into the fixed DLM_LOCKID_NAME_MAX-byte mname[]
array of an o2dlm_mle slab object, so a malformed message from a cluster
peer overflows the slab object by up to ~215 bytes: a heap out-of-bounds
write of attacker-controlled data, reachable by any node in the domain.

Reject an oversized name, the way dlm_master_request_handler() and the
other o2dlm receive handlers already do; the migration handler omits the
check entirely.  Conforming messages are unaffected.

The Linux kernel CVE team has assigned CVE-2026-89495 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 2.6.16 with commit 6714d8e86bf443f6f7af50f9d432025649f091f5 and fixed in 6.12.109 with commit f8658ee3327f73bd81c0bcd07cdeb5a8527fac98
	Issue introduced in 2.6.16 with commit 6714d8e86bf443f6f7af50f9d432025649f091f5 and fixed in 6.18.50 with commit de10cd3b062a5235af754925fcf49beb5a1109d4
	Issue introduced in 2.6.16 with commit 6714d8e86bf443f6f7af50f9d432025649f091f5 and fixed in 7.2.4 with commit 2487bea2098322669f0563baff53e797486b823f
	Issue introduced in 2.6.16 with commit 6714d8e86bf443f6f7af50f9d432025649f091f5 and fixed in 7.3-rc1 with commit ea5b5609305a8437bc955a0834a530c12246d78f

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-89495
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	fs/ocfs2/dlm/dlmmaster.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f8658ee3327f73bd81c0bcd07cdeb5a8527fac98
	https://git.kernel.org/stable/c/de10cd3b062a5235af754925fcf49beb5a1109d4
	https://git.kernel.org/stable/c/2487bea2098322669f0563baff53e797486b823f
	https://git.kernel.org/stable/c/ea5b5609305a8437bc955a0834a530c12246d78f