CVE-2025-40183

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

bpf: Fix metadatadst leak _bpfredirectneigh_v{4,6}

Cilium has a BPF egress gateway feature which forces outgoing K8s Pod traffic to pass through dedicated egress gateways which then SNAT the traffic in order to interact with stable IPs outside the cluster.

The traffic is directed to the gateway via vxlan tunnel in collect md mode. A recent BPF change utilized the bpfredirectneigh() helper to forward packets after the arrival and decap on vxlan, which turned out over time that the kmalloc-256 slab usage in kernel was ever-increasing.

The issue was that vxlan allocates the metadatadst object and attaches it through a fake dst entry to the skb. The latter was never released though given bpfredirectneigh() was merely setting the new dst entry via skbdst_set() without dropping an existing one first.