CVE-2026-89555

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

mpls: reload header after pskbmaypull()

mplsselectmultipath() calls mplsmultipathhash() 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 pskbmaypull() 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, pskbmaypull() calls

pskbexpandhead() 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 mplsselectmultipath

  Read of size 1 at addr ffff88800ecc6e20 by task ksoftirqd/1/23

  Call Trace:

   mplsselectmultipath

   mpls_forward

   _netifreceiveskblist_core

   netifreceiveskblistinternal

   napicompletedone

   grocellpoll

   _napipoll

   netrxaction

  Freed by task 23:

   kfree

   pskbexpandhead

   _pskbpull_tail

   mplsselectmultipath

Reload hdr from the current skb head after each successful pull before

deriving the inner IPv4 or IPv6 header pointer.