Re: [PATCH bpf] bpf: Fix metadata_dst leak __bpf_redirect_neigh_v{4,6}

[Simon Horman <horms@kernel.org>]

On Fri, Oct 03, 2025 at 09:34:18AM +0200, Daniel Borkmann wrote:
> 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 bpf_redirect_neigh() 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 metadata_dst object and attaches
> it through a fake dst entry to the skb. The latter was never released
> though given bpf_redirect_neigh() was merely setting the new dst entry
> via skb_dst_set() without dropping an existing one first.
> 
> Fixes: b4ab31414970 ("bpf: Add redirect_neigh helper as redirect drop-in")
> Reported-by: Yusuke Suzuki <yusuke.suzuki@isovalent.com>
> Reported-by: Julian Wiedmann <jwi@isovalent.com>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Martin KaFai Lau <martin.lau@kernel.org>
> Cc: Jakub Kicinski <kuba@kernel.org>
> Cc: Jordan Rife <jrife@google.com>

Reviewed-by: Simon Horman <horms@kernel.org>