netdev - Re: linux 3.13: problems with isatap tunnel device and UFO

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Date:	Fri, 21 Feb 2014 02:19:52 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Wolfgang Walter <linux@...m.de>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: linux 3.13: problems with isatap tunnel device and UFO

On Thu, Feb 20, 2014 at 04:43:41PM -0800, Cong Wang wrote:
> On Wed, Feb 19, 2014 at 6:44 PM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> > On Mon, Feb 17, 2014 at 05:09:16PM +0100, Hannes Frederic Sowa wrote:
> >> [+Cc Cong Wang]
> >>
> >> Hi Cong!
> >>
> >> In commit d949d826c09fb ("ipv6: Add generic UDP Tunnel segmentation") you
> >> patched ip6_offload.c:
> >>
> >> @@ -126,7 +128,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
> >>                 ipv6h = ipv6_hdr(skb);
> >>                 ipv6h->payload_len = htons(skb->len - skb->mac_len -
> >>                                            sizeof(*ipv6h));
> >> -               if (proto == IPPROTO_UDP) {
> >> +               if (!tunnel && proto == IPPROTO_UDP) {
> >>                         unfrag_ip6hlen = ip6_find_1stfragopt(skb, &prevhdr);
> >>                         fptr = (struct frag_hdr *)(skb_network_header(skb) +
> >>                                 unfrag_ip6hlen);
> >>
> >>
> >> I wonder about the !tunnel exception. This now seems to be a problem in sit
> >> ufo output path, where we don't update fragmentation offsets any more thus
> >> generating invalid frames.
> >>
> >> I am not too firm with segmentation in case of tunnels but don't we need to
> >> always update the fragmentation offset no matter what, if upper gso callback
> >> produced more segments?
> >
> > Not perfect nor clean (well, I don't know).
> >
> > The idea is to have the segmentation at the first guessed tunnel
> > header cut. I don't know how to deal with stacked tunnels yet, I guess
> > we need to have a bit more state in the skb. Just to maybe keep the discussion
> > going...
> 
> Does the following patch help?

> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
> index 1e8683b..516b889 100644
> --- a/net/ipv6/ip6_offload.c
> +++ b/net/ipv6/ip6_offload.c
> @@ -89,7 +89,7 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
>  	unsigned int unfrag_ip6hlen;
>  	u8 *prevhdr;
>  	int offset = 0;
> -	bool tunnel;
> +	bool udpfrag, encap;
>  	int nhoff;
>  
>  	if (unlikely(skb_shinfo(skb)->gso_type &
> @@ -110,8 +110,8 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
>  	if (unlikely(!pskb_may_pull(skb, sizeof(*ipv6h))))
>  		goto out;
>  
> -	tunnel = SKB_GSO_CB(skb)->encap_level > 0;
> -	if (tunnel)
> +	encap = SKB_GSO_CB(skb)->encap_level > 0;
> +	if (encap)
>  		features = skb->dev->hw_enc_features & netif_skb_features(skb);
>  	SKB_GSO_CB(skb)->encap_level += sizeof(*ipv6h);
>  
> @@ -130,16 +130,17 @@ static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
>  	if (IS_ERR(segs))
>  		goto out;
>  
> +	udpfrag = !!skb->encapsulation && proto == IPPROTO_UDP;

The problem in general is that skb->encapsulation does not get reset as in GRE
or UDP_TUNNEL gso handler when traversing up the gso stack (e.g. from
another ipv6_gso_segment or inet_gso_segment.

skb->encapsulation is unreliable here.

Btw. IPv4 has the same problem and does not update fragment offsets,
so we cannot adapt the code from there.

Either we track inner_network_protocol in SKB_GSO_CB or try my proposal.

>  	for (skb = segs; skb; skb = skb->next) {
>  		ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
>  		ipv6h->payload_len = htons(skb->len - nhoff - sizeof(*ipv6h));
> -		if (tunnel) {
> +		if (encap) {
>  			skb_reset_inner_headers(skb);
>  			skb->encapsulation = 1;
>  		}
>  		skb->network_header = (u8 *)ipv6h - skb->head;
>  
> -		if (!tunnel && proto == IPPROTO_UDP) {
> +		if (udpfrag) {
>  			unfrag_ip6hlen = ip6_find_1stfragopt(skb, &prevhdr);
>  			fptr = (struct frag_hdr *)((u8 *)ipv6h + unfrag_ip6hlen);
>  			fptr->frag_off = htons(offset);

Greetings,

  Hannes

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