Bug 2532032 (CVE-2026-89555)

Summary:	CVE-2026-89555 kernel: mpls: reload header after pskb_may_pull()
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:	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 Multiprotocol Label Switching (MPLS) subsystem. When processing specially crafted Geneve packets through an MPLS multipath setup, a use-after-free vulnerability occurs. This issue arises because a cached header pointer (`hdr`) is not reloaded after `pskb_may_pull()` potentially reallocates the packet buffer, leading to `hdr` pointing to freed memory. A remote attacker could exploit this to trigger a kernel crash, resulting in a denial of service.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
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 2026-09-11 20:07:05 UTC

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

mpls: reload header after pskb_may_pull()

mpls_select_multipath() calls mpls_multipath_hash() to choose a nexthop
when an MPLS route has multiple nexthops.  While walking the MPLS label
stack, the hash routine caches hdr for the current label.  After finding
the bottom-of-stack label, it calls pskb_may_pull() before reading the
inner IP header.

If an skb is constructed with the inner IP header in nonlinear data and
insufficient tailroom in the linear head, pskb_may_pull() calls
pskb_expand_head() to replace the skb head and free the old one.  This
leaves hdr pointing to freed memory.  The IPv6 path can invalidate hdr
again when it performs a second pull for the larger header.

The issue was found through static analysis.  A reproducer sending a legal
Geneve packet through a bareudp/MPLS multipath setup triggered the same
KASAN report in 2 of 2 unpatched runs:

  BUG: KASAN: slab-use-after-free in mpls_select_multipath
  Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23

  Call Trace:
   mpls_select_multipath
   mpls_forward
   __netif_receive_skb_list_core
   netif_receive_skb_list_internal
   napi_complete_done
   gro_cell_poll
   __napi_poll
   net_rx_action

  Freed by task 23:
   kfree
   pskb_expand_head
   __pskb_pull_tail
   mpls_select_multipath

Reload hdr from the current skb head after each successful pull before
deriving the inner IPv4 or IPv6 header pointer.

Comment 1 Mauro Matteo Cascella 2026-09-14 10:11:17 UTC

Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89555.mbox