Re: [PATCH net v4 3/4] ipmr: set up GSO state for tunnel vifs

[Simon Horman <horms@kernel.org>]

On Sun, Nov 01, 2026 at 05:42:31PM +0100, Julius Bairaktaris wrote:
> ip_encap() pushes the outer IPv4 header but does not set SKB_GSO_IPXIP4,
> skb->encapsulation or the inner headers. A GSO packet forwarded to a
> VIFF_TUNNEL vif is then rejected by ipip_gso_segment() and dropped in
> validate_xmit_skb(), after being counted as sent. A device with UDP
> segmentation offload is handed a GSO packet whose transport header
> points at the inner IP header.
> 
> Call iptunnel_handle_offloads() and skb_set_inner_ipproto() as
> ipip_tunnel_xmit() does, reserve one outer IP ID per segment as
> iptunnel_xmit() does, and set the outer length with iph_set_totlen(),
> since a GSO packet plus the outer header can exceed 64 KB. A GSO packet
> that GRE or UDP tunnel GRO marked as encapsulated already uses the inner
> headers for its own tunnel; drop it, as segmentation did before.
> 
> Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
> Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>

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