Re: [PATCH v4 net-next 06/14] ipv6/gro: insert temporary HBH/jumbo header

[Alexander H Duyck <alexander.duyck@gmail.com>]

On Wed, 2022-03-09 at 21:46 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> Following patch will add GRO_IPV6_MAX_SIZE, allowing gro to build
> BIG TCP ipv6 packets (bigger than 64K).
> 

This looks like it belongs in the next patch, not this one. This patch
is adding the HBH header.

> This patch changes ipv6_gro_complete() to insert a HBH/jumbo header
> so that resulting packet can go through IPv6/TCP stacks.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
>  net/ipv6/ip6_offload.c | 32 ++++++++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
> index a6a6c1539c28d242ef8c35fcd5ce900512ce912d..d12dba2dd5354dbb79bb80df4038dec2544cddeb 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -342,15 +342,43 @@ static struct sk_buff *ip4ip6_gro_receive(struct list_head *head,
>  INDIRECT_CALLABLE_SCOPE int ipv6_gro_complete(struct sk_buff *skb, int nhoff)
>  {
>  	const struct net_offload *ops;
> -	struct ipv6hdr *iph = (struct ipv6hdr *)(skb->data + nhoff);
> +	struct ipv6hdr *iph;
>  	int err = -ENOSYS;
> +	u32 payload_len;
>  
>  	if (skb->encapsulation) {
>  		skb_set_inner_protocol(skb, cpu_to_be16(ETH_P_IPV6));
>  		skb_set_inner_network_header(skb, nhoff);
>  	}
>  
> -	iph->payload_len = htons(skb->len - nhoff - sizeof(*iph));
> +	payload_len = skb->len - nhoff - sizeof(*iph);
> +	if (unlikely(payload_len > IPV6_MAXPLEN)) {
> +		struct hop_jumbo_hdr *hop_jumbo;
> +		int hoplen = sizeof(*hop_jumbo);
> +
> +		/* Move network header left */
> +		memmove(skb_mac_header(skb) - hoplen, skb_mac_header(skb),
> +			skb->transport_header - skb->mac_header);
> +		skb->data -= hoplen;
> +		skb->len += hoplen;
> +		skb->mac_header -= hoplen;
> +		skb->network_header -= hoplen;
> +		iph = (struct ipv6hdr *)(skb->data + nhoff);
> +		hop_jumbo = (struct hop_jumbo_hdr *)(iph + 1);
> +
> +		/* Build hop-by-hop options */
> +		hop_jumbo->nexthdr = iph->nexthdr;
> +		hop_jumbo->hdrlen = 0;
> +		hop_jumbo->tlv_type = IPV6_TLV_JUMBO;
> +		hop_jumbo->tlv_len = 4;
> +		hop_jumbo->jumbo_payload_len = htonl(payload_len + hoplen);
> +
> +		iph->nexthdr = NEXTHDR_HOP;
> +		iph->payload_len = 0;
> +	} else {
> +		iph = (struct ipv6hdr *)(skb->data + nhoff);
> +		iph->payload_len = htons(payload_len);
> +	}
>  
>  	nhoff += sizeof(*iph) + ipv6_exthdrs_len(iph, &ops);
>  	if (WARN_ON(!ops || !ops->callbacks.gro_complete))