netdev - Re: [PATCH net-next 06/15] ipv6/gro: insert temporary HBH/jumbo header

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Message-ID: <99e23f620a798d6cfb9c9b20fb37ba6ba8137a05.camel@redhat.com>
Date:   Thu, 03 Feb 2022 10:19:59 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Coco Li <lixiaoyan@...gle.com>
Subject: Re: [PATCH net-next 06/15] ipv6/gro: insert temporary HBH/jumbo
 header

On Wed, 2022-02-02 at 17:51 -0800, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> Following patch will add GRO_IPV6_MAX_SIZE, allowing gro to build
> BIG TCP ipv6 packets (bigger than 64K).
> 
> 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@...gle.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 d37a79a8554e92a1dcaa6fd023cafe2114841ece..dac6f60436e167a3d979fef02f25fc039c6ed37d 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -318,15 +318,43 @@ 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);

I was wondering if we should check for enough headroom and what about
TCP over UDP tunnel, then I read the next patch ;) 

I think a comment here referring to the constraint enforced by
skb_gro_receive() could help, or perhaps squashing the 2 patches?!?

Thanks!

Paolo