CVE-2026-98103
igmp: convert struct ip_sf_list to RCU
Published Sep 25, 2026
CVSS 3.1 · 5.5 Medium
EPSS < 1%
KEV · Not listed
Description
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.
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.
Affected Products
-
CVE record
-
NVD configurations
No data
-
Red Hat packages
No data
-
OpenCVE enrichment
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
| Vendor | Product | Versions | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux Kernel |
|
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Linux | Linux Kernel |
|
Remediation
Tracking
Advisories
| Source | ID | Title |
|---|---|---|
 Debian DLA |
DLA-4817-1 | linux-6.12 security update |
 Debian DSA |
DSA-6528-1 | linux security update |
 Ubuntu USN |
USN-9019-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9020-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9022-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9023-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9024-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9025-1 | Linux kernel vulnerabilities |
| Ubuntu USN |
USN-9026-1 | Linux kernel (Azure) vulnerabilities |
| Ubuntu USN |
USN-9039-1 | Linux kernel (Azure CVM) vulnerabilities |
| Ubuntu USN |
USN-9040-1 | Linux kernel (Low Latency NVIDIA) vulnerabilities |
| Ubuntu USN |
USN-9066-1 | Linux kernel (HWE) vulnerabilities |
| Ubuntu USN |
USN-9091-1 | Linux kernel (NVIDIA Tegra) vulnerabilities |
Metrics
No CVSS v4.0
Attack Vector Local
Attack Complexity Low
Privileges Required Low
Scope Unchanged
Confidentiality Impact None
Integrity Impact None
Availability Impact High
User Interaction None
No CVSS v3.0
No CVSS v2
This CVE is not in the KEV list.
Exploit prediction score: < 1% (0.168% probability within 30 days)
Key SSVC decision points have not yet been added.
References
History
Oct 21, 2026 1:15 PM
Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
Sep 29, 2026 1:15 PM
Weaknesses updated. Added references. Scoring metrics updated
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Weaknesses | CWE-764 | |
| References |
| |
| Metrics |
threat_severity
|
cvssV3_1
|
Sep 25, 2026 10:45 AM
Description updated. Title updated. First appearance in the feed. Affected versions updated. Affected vendors updated. Added references
View changes
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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. | |
| Title | igmp: convert struct ip_sf_list to RCU | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
Subscriptions
Weaknesses
