---
id: CVE-2026-98103
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  igmp: convert struct ip_sf_list to RCU

  Commit 23d2b94043ca ("igmp: Add ip_mc_list lock in ip_check_mc_rcu")
  added spin_lock_bh(&im->lock) to ip_check_mc_rcu() to preve…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  igmp: convert struct ip_sf_list to RCU

  Commit 23d2b94043ca ("igmp: Add ip_mc_list lock in ip_check_mc_rcu")
  added spin_lock_bh(&im->lock) to ip_check_mc_rcu() to preve…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 23d2b94043ca8835bd1e67749020e839f396a1c2 <
    f5182dfad54277267a8cb0c004a9cd4cf35aeebb
  - >-
    Linux >= 23d2b94043ca8835bd1e67749020e839f396a1c2 <
    d3011d1f293478c730aa0870490afa145c37600e
  - >-
    Linux >= 23d2b94043ca8835bd1e67749020e839f396a1c2 <
    e3206419bdb04e2087d8cc6be324df8639b3fac5
  - >-
    Linux >= 23d2b94043ca8835bd1e67749020e839f396a1c2 <
    2987ee196c88dbde0463dc87d5fb209c684e34a2
  - Linux b24065948ae6c48c9e20891f8cfe9850f1d748be
  - Linux e9924c4204ede999b0515fd31a370a1e27f676bc
  - Linux 78967749984cf3614de346c90f3e259ff8272735
  - Linux 4768973dffed4d0126854514335ed4fe87bec1ab
  - Linux d84708451d9041dff8a81e3718f821f12d2eb6c5
  - Linux ddd7e8b7b84836c584a284b98ca9bd7a348a0558
  - Linux 961447ff60291b91e27d5c32fa549c1411ad3b70
  - Linux d1a3c6d5925a8d00a32c5ef2d674dd9c0ce89c95
  - Linux >= 4.4.284 < 4.5
  - Linux >= 4.9.283 < 4.10
  - Linux >= 4.14.247 < 4.15
  - Linux >= 4.19.207 < 4.20
  - Linux >= 5.4.145 < 5.5
  - Linux >= 5.10.64 < 5.11
  - Linux >= 5.13.16 < 5.14
  - Linux >= 5.14.3 < 5.15
  - Linux 5.15
published: '2026-09-25'
updated: '2026-09-25'
sourceUpdated: '2026-09-25T11:17:40.613'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-98103'
references:
  - url: 'https://git.kernel.org/stable/c/2987ee196c88dbde0463dc87d5fb209c684e34a2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d3011d1f293478c730aa0870490afa145c37600e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e3206419bdb04e2087d8cc6be324df8639b3fac5'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f5182dfad54277267a8cb0c004a9cd4cf35aeebb'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-25T11:06:38.827Z'
---

## Overview

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

igmp: convert struct ip_sf_list to RCU

Commit 23d2b94043ca ("igmp: Add ip_mc_list lock in ip_check_mc_rcu")
added spin_lock_bh(&im->lock) to ip_check_mc_rcu() to prevent a
use-after-free while iterating im->sources during concurrent deletions.

However, ip_check_mc_rcu() is called from RCU read-side critical
sections in packet receive and route lookup fast paths (e.g.
__mkroute_output(), ip_route_input_rcu(), and __udp4_lib_rcv()).

When igmpv3_send_cr() or igmpv3_send_report() holds &pmc->lock and
calls add_grec() -> igmpv3_newpack() -> ip_route_output_ports(),
an XFRM policy matching a multicast destination triggers
xfrm_tmpl_resolve_one() -> xfrm4_get_saddr() -> __mkroute_output() ->
ip_check_mc_rcu(). This attempts to acquire &im->lock while &pmc->lock
is already held on the same CPU, triggering a lockdep recursive locking
warning / deadlock.

Fix this by converting IPv4 struct ip_sf_list to RCU, mirroring the
IPv6 implementation in net/ipv6/mcast.c:

1. Add struct rcu_head to struct ip_sf_list and annotate sf_next,
   sources, and tomb as __rcu pointers.
2. Use rcu_assign_pointer() and kfree_rcu() for list updates and
   deletions.
3. Remove spin_lock_bh(&im->lock) from ip_check_mc_rcu() and traverse
   im->sources locklessly with for_each_psf_rcu(), reading and writing
   counter fields with READ_ONCE() and WRITE_ONCE().

Note: RCU conversion of /proc/net/mcfilter will be done in a
separate patch.

## Remediation

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