Bug 2516585 (CVE-2026-72429)

Summary:	CVE-2026-72429 kernel: ipv6: ioam: fix type confusion of dst_entry
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	rhel-process-autobot, 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 In-situ Operations, Administration, and Maintenance (IOAM) subsystem. This vulnerability arises from a type confusion where a dummy network destination entry (dst_entry) is incorrectly handled as a routing information structure (rt6_info). When this dummy entry is stored in the IOAM Lightweight Tunnel (LWT) state and passed to functions expecting a full rt6_info structure, it leads to an invalid cast. This can result in an invalid pointer access, potentially causing system instability or a denial of service.	Story Points:	---
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Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-08-15 06:20:19 UTC

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

ipv6: ioam: fix type confusion of dst_entry

IOAM uses a dummy dst_entry(null_dst) to mark that the destination should
not be changed after the transformation. This dst is stored in the IOAM lwt
state and may be passed to dst_cache_set_ip6().

However, the IPv6 dst cache path eventually calls rt6_get_cookie(), which
treats the dst_entry as part of a struct rt6_info. Since the null_dst was
embedded directly as a struct dst_entry in struct ioam6_lwt, this resulted
in an invalid cast and rt6_get_cookie() reading fields from the wrong
object.

In practice, the wrong cookie is not used while dst->obsolete is zero, but
rt6_get_cookie() may also access per-cpu value when rt->sernum is
zero. In this case, rt->sernum aliases ioam6_lwt::cache::reset_ts, which
can become zero, making this a potential invalid pointer access.

Fix this by embedding a full struct rt6_info for the dummy IPv6 route and
passing its dst member to the dst APIs.

Comment 1 Keith Grant 2026-08-19 16:26:59 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081527-CVE-2026-72429-b4e6@gregkh/T