---
id: CVE-2026-23124
title: 'ipv6: annotate data-race in ndisc_router_discovery()'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv6: annotate data-race in ndisc_router_discovery()

  syzbot found that ndisc_router_discovery() could read and write
  in6_dev->ra_mtu without holding a lock [1]

  This l…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    4630897eb1a039b5d7b737b8dc9521d9d4b568b5
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    2619499169fb1c2ac4974b0f2d87767fb543582b
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    fad8f4ff7928f4d52a062ffdcffa484989c79c47
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    2a2b9d25f801afecf2f83cacce98afa8fd73e3c9
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    e3c1040252e598f7b4e33a42dc7c38519bc22428
  - >-
    Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 <
    9a063f96d87efc3a6cc667f8de096a3d38d74bb5
  - Linux 5.15
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-06-10T20:40:30.553217Z'
published: '2026-02-14'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T18:25:32.245Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23124'
references:
  - url: 'https://git.kernel.org/stable/c/4630897eb1a039b5d7b737b8dc9521d9d4b568b5'
  - url: 'https://git.kernel.org/stable/c/2619499169fb1c2ac4974b0f2d87767fb543582b'
  - url: 'https://git.kernel.org/stable/c/fad8f4ff7928f4d52a062ffdcffa484989c79c47'
  - url: 'https://git.kernel.org/stable/c/2a2b9d25f801afecf2f83cacce98afa8fd73e3c9'
  - url: 'https://git.kernel.org/stable/c/e3c1040252e598f7b4e33a42dc7c38519bc22428'
  - url: 'https://git.kernel.org/stable/c/9a063f96d87efc3a6cc667f8de096a3d38d74bb5'
tags:
  - cve.org
epss: 0.00134
epssPercentile: 0.02572
ingestedAt: '2026-10-19T18:35:50.102Z'
---

## Overview

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

ipv6: annotate data-race in ndisc_router_discovery()

syzbot found that ndisc_router_discovery() could read and write
in6_dev->ra_mtu without holding a lock [1]

This looks fine, IFLA_INET6_RA_MTU is best effort.

Add READ_ONCE()/WRITE_ONCE() to document the race.

Note that we might also reject illegal MTU values
(mtu < IPV6_MIN_MTU || mtu > skb->dev->mtu) in a future patch.

[1]
BUG: KCSAN: data-race in ndisc_router_discovery / ndisc_router_discovery

read to 0xffff888119809c20 of 4 bytes by task 25817 on cpu 1:
  ndisc_router_discovery+0x151d/0x1c90 net/ipv6/ndisc.c:1558
  ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
  icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
  ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
  ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
  NF_HOOK include/linux/netfilter.h:318 [inline]
  ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
  ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
  dst_input include/net/dst.h:474 [inline]
  ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...

write to 0xffff888119809c20 of 4 bytes by task 25816 on cpu 0:
  ndisc_router_discovery+0x155a/0x1c90 net/ipv6/ndisc.c:1559
  ndisc_rcv+0x2ad/0x3d0 net/ipv6/ndisc.c:1841
  icmpv6_rcv+0xe5a/0x12f0 net/ipv6/icmp.c:989
  ip6_protocol_deliver_rcu+0xb2a/0x10d0 net/ipv6/ip6_input.c:438
  ip6_input_finish+0xf0/0x1d0 net/ipv6/ip6_input.c:489
  NF_HOOK include/linux/netfilter.h:318 [inline]
  ip6_input+0x5e/0x140 net/ipv6/ip6_input.c:500
  ip6_mc_input+0x27c/0x470 net/ipv6/ip6_input.c:590
  dst_input include/net/dst.h:474 [inline]
  ip6_rcv_finish+0x336/0x340 net/ipv6/ip6_input.c:79
...

value changed: 0x00000000 -> 0xe5400659

## Affected

- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < 4630897eb1a039b5d7b737b8dc9521d9d4b568b5`
- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < 2619499169fb1c2ac4974b0f2d87767fb543582b`
- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < fad8f4ff7928f4d52a062ffdcffa484989c79c47`
- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < 2a2b9d25f801afecf2f83cacce98afa8fd73e3c9`
- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < e3c1040252e598f7b4e33a42dc7c38519bc22428`
- `Linux >= 49b99da2c9ce13ffcd93fe3a0f5670791c1d76f7 < 9a063f96d87efc3a6cc667f8de096a3d38d74bb5`
- `Linux 5.15`

## Remediation

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