---
id: CVE-2026-99117
title: 'net: bridge: mcast: don''t truncate the port group walk on teardown'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: bridge: mcast: don't truncate the port group walk on teardown

  __br_multicast_disable_port_ctx() and br_multicast_del_port() walk
  port->mglist with hlist_for_each_…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 <
    8243d587a081e790ad96e80d48eef44d9f7ef005
  - >-
    Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 <
    b45e8c24608c992d1e2cea047eb5bcbfa537f86b
  - >-
    Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 <
    5a3f7a683aee56e1f15c9d53041f3236767eaae7
  - Linux 5.10
published: '2026-10-28'
updated: '2026-10-28'
sourceUpdated: '2026-10-28T10:34:33.874Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-99117'
references:
  - url: 'https://git.kernel.org/stable/c/8243d587a081e790ad96e80d48eef44d9f7ef005'
  - url: 'https://git.kernel.org/stable/c/b45e8c24608c992d1e2cea047eb5bcbfa537f86b'
  - url: 'https://git.kernel.org/stable/c/5a3f7a683aee56e1f15c9d53041f3236767eaae7'
tags:
  - cve.org
ingestedAt: '2026-10-28T11:09:40.449Z'
---

## Overview

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

net: bridge: mcast: don't truncate the port group walk on teardown

__br_multicast_disable_port_ctx() and br_multicast_del_port() walk
port->mglist with hlist_for_each_entry_safe(). However,
br_multicast_find_del_pg() can also delete other entries from the same
list through br_multicast_fwd_src_remove() or __fwd_del_star_excl().

If such an entry is the iterator's saved next node, hlist_del_init()
clears its ->next and terminates the walk early. The reproducer triggers
this in both teardown walks, leaving port groups in the bridge mdb with
a dangling ->key.port after del_nbp() frees the port:

  BUG: KASAN: slab-use-after-free in __mdb_fill_info+0x1191/0x1320
   __mdb_fill_info+0x1191/0x1320
   br_mdb_dump+0x594/0xe40
   rtnl_mdb_dump+0x1cf/0x5d0

Use hlist_del_init_rcu() to unlink the group while preserving ->next.
br_multicast_del_pg() and the teardown walks run under
br->multicast_lock. The GC worker must acquire the same lock before
detaching the group for destruction, so the node remains alive while
the walk uses the preserved pointer.

Preserving ->next means a walk can now reach a group that an earlier
iteration already deleted as a side effect. That group is off mp->ports,
so br_multicast_find_del_pg() would fall through its port scan and hit
the trailing WARN_ON(1). Skip such groups at the top of that helper: a
port group is put on port->mglist when it is created and only unlinked
when it is deleted, so hlist_unhashed() identifies exactly this case.

## Affected

- `Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 < 8243d587a081e790ad96e80d48eef44d9f7ef005`
- `Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 < b45e8c24608c992d1e2cea047eb5bcbfa537f86b`
- `Linux >= b08123684bd55fa6d6ee4b52d4ae3040fadb5aa2 < 5a3f7a683aee56e1f15c9d53041f3236767eaae7`
- `Linux 5.10`

## Remediation

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