Bug 2541373 (CVE-2026-98102)

Summary:	CVE-2026-98102 kernel: ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's IPv6 multicast implementation. When removing an active multicast source filter, an internal list pointer is updated before the read-copy update (RCU) grace period elapses. A local user can exploit this race condition during concurrent multicast address lookups, causing readers to miss active sources and inspect deleted entries, potentially leading to incorrect network traffic filtering or a denial of service (DoS).	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
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Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-09-25 11:37:01 UTC

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

ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()

When removing a source filter whose count reaches zero, ip6_mc_del1_src()
unlinks psf from pmc->mca_sources. If the filter was previously active,
the code moved psf directly into pmc->mca_tomb by updating psf->sf_next.

Because pmc->mca_sources is traversed locklessly under RCU (e.g. by
ipv6_chk_mcast_addr()), mutating psf->sf_next before a grace period
elapses diverts concurrent readers to the tombstone list. Consequently,
readers miss remaining active sources in pmc->mca_sources and improperly
examine deleted tombstone entries.

Fix this by allocating a new tombstone node for pmc->mca_tomb (as done
in sf_setstate()) and retiring the original psf via kfree_rcu().

Comment 1 Keith Grant 2026-09-25 19:37:14 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98102.mbox