netdev - Re: [PATCH ipsec] esp6: support ipv6 nexthdrs process for beet gso segment

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Date:   Wed, 15 Apr 2020 11:56:20 +0200
From:   Sabrina Dubroca <sd@...asysnail.net>
To:     Xin Long <lucien.xin@...il.com>
Cc:     netdev@...r.kernel.org,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH ipsec] esp6: support ipv6 nexthdrs process for beet gso
 segment

2020-04-10, 17:07:31 +0800, Xin Long wrote:
> For beet mode, when it's ipv6 inner address with nexthdrs set,
> the packet format might be:
> 
>     ----------------------------------------------------
>     | outer  |     | dest |     |      |  ESP    | ESP |
>     | IP6 hdr| ESP | opts.| TCP | Data | Trailer | ICV |
>     ----------------------------------------------------
> 
> Before doing gso segment in xfrm6_beet_gso_segment(), it should
> skip all nexthdrs and get the real transport proto, and set
> transport_header properly.
> 
> This patch is to fix it by simply calling ipv6_skip_exthdr()
> in xfrm6_beet_gso_segment().
> 
> Fixes: 7f9e40eb18a9 ("esp6: add gso_segment for esp6 beet mode")
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/ipv6/esp6_offload.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/esp6_offload.c b/net/ipv6/esp6_offload.c
> index b828508..021f58c 100644
> --- a/net/ipv6/esp6_offload.c
> +++ b/net/ipv6/esp6_offload.c
> @@ -173,7 +173,7 @@ static struct sk_buff *xfrm6_beet_gso_segment(struct xfrm_state *x,
>  	struct xfrm_offload *xo = xfrm_offload(skb);
>  	struct sk_buff *segs = ERR_PTR(-EINVAL);
>  	const struct net_offload *ops;
> -	int proto = xo->proto;
> +	u8 proto = xo->proto;
>  
>  	skb->transport_header += x->props.header_len;
>  
> @@ -184,7 +184,13 @@ static struct sk_buff *xfrm6_beet_gso_segment(struct xfrm_state *x,
>  		proto = ph->nexthdr;
>  	}
>  
> -	if (x->sel.family != AF_INET6) {
> +	if (x->sel.family == AF_INET6) {
> +		int offset = skb_transport_offset(skb);
> +		__be16 frag;
> +
> +		offset = ipv6_skip_exthdr(skb, offset, &proto, &frag);
> +		skb->transport_header += offset;

This seems a bit wrong: we start with offset = transport_offset, then
ipv6_skip_exthdr adds the size of the extension headers to it.

In a simple case where there's no extension header, ipv6_skip_exthdr
returns offset. Now we add offset to skb->transport_header, so
transport_header is increased, but it shouldn't have changed.

What am I missing?

Thanks.

-- 
Sabrina