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

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

ocfs2: bound namelen in dlmmigraterequesthandler

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:

- dlmmigraterequesthandler() passes migrate->namelen unchecked to dlminitmle(), which memcpy()s it into the 32-byte mname[] of an o2dlmmle slab object: a heap out-of-bounds write of up to ~215 attacker-controlled bytes.

- dlmmiglockreshandler() passes mres->locknamelen unchecked to dlminitlockres(), which memcpy()s it into the 32-byte o2dlmlockname slab object: a heap out-of-bounds write of up to ~223 bytes.

- the same handler trusts mres->numlocks without checking that the message is large enough to hold that many entries, so dlmprocessrecoverydata() walks mres->ml[] past the kmalloc(datalen) copy and trips a BUGON (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 locknamelen, numlocks, 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 kmemcache/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 DLMMIGRATEREQUEST message trusts the peer-supplied name length (migrate->namelen) without bounding it. dlminitmle() then copies that many bytes into the fixed DLMLOCKIDNAMEMAX-byte mname[] array of an o2dlmmle 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 dlmmasterrequesthandler() and the other o2dlm receive handlers already do; the migration handler omits the check entirely. Conforming messages are unaffected.