CVE-2026-90111

Summary

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

ip6mr: do not clone dst in ip6mr_cache_report()

IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU. When an ingress multicast packet misses MFC lookup, ip6mr_cache_unresolved() places the skb onto the unresolved queue, escaping the receive-side RCU grace period.

If the underlying route is deleted and freed, and the MFC queue is later resolved with a wrong parent interface, ip6_mr_forward() invokes ip6mr_cache_report(…, MRT6MSG_WRONGMIF), which executes dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab use-after-free.

Report packets queued to mroute6_sk (a raw socket) and netlink notifications do not require an attached dst entry.

Fix this by:

1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs do not hold a dst.
2. Dropping skb_dst before queuing unresolved skbs in ip6mr_cache_unresolved(), matching the fact that multicast forwarding resolves outgoing routes anew via ip6_route_output().

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/4a674afaae4136c71943aa3e35d433676fd40e8f
• https://git.kernel.org/stable/c/235b42b5860189eb8c27c36435ad932cae65a734

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