GHSA-2HRC-MWQG-6FR2
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31In 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:
- Add struct rcu_head to struct ip_sf_list and annotate sf_next, sources, and tomb as __rcu pointers.
- Use rcu_assign_pointer() and kfree_rcu() for list updates and deletions.
- 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.
{
"affected": [],
"aliases": [
"CVE-2026-98103"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:40Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nigmp: convert struct ip_sf_list to RCU\n\nCommit 23d2b94043ca (\"igmp: Add ip_mc_list lock in ip_check_mc_rcu\")\nadded spin_lock_bh(\u0026im-\u003elock) to ip_check_mc_rcu() to prevent a\nuse-after-free while iterating im-\u003esources during concurrent deletions.\n\nHowever, ip_check_mc_rcu() is called from RCU read-side critical\nsections in packet receive and route lookup fast paths (e.g.\n__mkroute_output(), ip_route_input_rcu(), and __udp4_lib_rcv()).\n\nWhen igmpv3_send_cr() or igmpv3_send_report() holds \u0026pmc-\u003elock and\ncalls add_grec() -\u003e igmpv3_newpack() -\u003e ip_route_output_ports(),\nan XFRM policy matching a multicast destination triggers\nxfrm_tmpl_resolve_one() -\u003e xfrm4_get_saddr() -\u003e __mkroute_output() -\u003e\nip_check_mc_rcu(). This attempts to acquire \u0026im-\u003elock while \u0026pmc-\u003elock\nis already held on the same CPU, triggering a lockdep recursive locking\nwarning / deadlock.\n\nFix this by converting IPv4 struct ip_sf_list to RCU, mirroring the\nIPv6 implementation in net/ipv6/mcast.c:\n\n1. Add struct rcu_head to struct ip_sf_list and annotate sf_next,\n sources, and tomb as __rcu pointers.\n2. Use rcu_assign_pointer() and kfree_rcu() for list updates and\n deletions.\n3. Remove spin_lock_bh(\u0026im-\u003elock) from ip_check_mc_rcu() and traverse\n im-\u003esources locklessly with for_each_psf_rcu(), reading and writing\n counter fields with READ_ONCE() and WRITE_ONCE().\n\nNote: RCU conversion of /proc/net/mcfilter will be done in a\nseparate patch.",
"id": "GHSA-2hrc-mwqg-6fr2",
"modified": "2026-09-25T12:31:36Z",
"published": "2026-09-25T12:31:36Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98103"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2987ee196c88dbde0463dc87d5fb209c684e34a2"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d3011d1f293478c730aa0870490afa145c37600e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e3206419bdb04e2087d8cc6be324df8639b3fac5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f5182dfad54277267a8cb0c004a9cd4cf35aeebb"
}
],
"schema_version": "1.4.0",
"severity": []
}
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