CVE-2026-89555

Summary

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.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/fed638a248116b8a249bd4202d28e5934bdc65ad
• https://git.kernel.org/stable/c/d82b90a38c2ca8a0694428eab0e9551c23f2447d
• https://git.kernel.org/stable/c/49d38c1b4390412f8950d33dfaee0ccbd17beb81
• https://git.kernel.org/stable/c/29e63b8d9fc150cc191b1c6eb7e16e1247e1b650

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