CVE-2026-89555

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.