netdev - Re: [PATCH] NET: SRv6: seg6_local: Fixed SRH processing when segments left is 0

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Date:   Tue, 2 Feb 2021 10:52:33 +0100
From:   Ahmed Abdelsalam <ahabdels.dev@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Suprit Japagal <suprit.japagal@...il.com>, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org,
        David Lebrun <david.lebrun@...ouvain.be>,
        netdev@...r.kernel.org
Subject: Re: [PATCH] NET: SRv6: seg6_local: Fixed SRH processing when
 segments left is 0

The current implementation is correct. This patch is introducing incorrect 
symantic to SRv6 End and End.T behaviors.   

SRv6 End and End.T behaviors (among other behaviors) are defined in the 
SRv6 Network Programming draft (Soon to published as an RFC) [1].

SRv6 End and End.T behaviors are used to implement Traffic Engineering (TE)
use-cases, where a node recieves the packet and send it to the next SID from 
the SRH SIDList. 

Packets processed by End and End.T behaviors can not have a Segment Left Value 
of zero. 

Please refer to sections 4.1 and 4.3 of [1]. 


[1]https://tools.ietf.org/html/draft-ietf-spring-srv6-network-programming-28

Ahmed 


On Sun, 31 Jan 2021 10:33:14 -0700
David Ahern <dsahern@...il.com> wrote:

> [ cc David Lebrun, author of the original code ]
> 
> On 1/31/21 6:08 AM, Suprit Japagal wrote:
> > From: "Suprit.Japagal" <suprit.japagal@...il.com>
> > 
> > According to the standard IETF RFC 8754, section 4.3.1.1
> > (https://tools.ietf.org/html/rfc8754#section-4.3.1.1)
> > When the segments left in SRH equals to 0, proceed to process the
> > next header in the packet, whose type is identified by the
> > Next header field of the routing header.
> > 
> > Signed-off-by: Suprit.Japagal <suprit.japagal@...il.com>
> > ---
> >  net/ipv6/seg6_local.c | 54 +++++++++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 48 insertions(+), 6 deletions(-)
> > 
> > diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c
> > index b07f7c1..b17f9dc 100644
> > --- a/net/ipv6/seg6_local.c
> > +++ b/net/ipv6/seg6_local.c
> > @@ -273,11 +273,25 @@ static int input_action_end(struct sk_buff *skb, struct seg6_local_lwt *slwt)
> >  {
> >  	struct ipv6_sr_hdr *srh;
> >  
> > -	srh = get_and_validate_srh(skb);
> > +	srh = get_srh(skb);
> >  	if (!srh)
> >  		goto drop;
> >  
> > -	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +#ifdef CONFIG_IPV6_SEG6_HMAC
> > +	if (srh->segments_left > 0)
> > +		if (!seg6_hmac_validate_skb(skb))
> > +			goto drop;
> > +#endif
> > +
> > +	if (srh->segments_left == 0) {
> > +		if (!decap_and_validate(skb, srh->nexthdr))
> > +			goto drop;
> > +
> > +		if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
> > +			goto drop;
> > +	} else {
> > +		advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +	}
> >  
> >  	seg6_lookup_nexthop(skb, NULL, 0);
> >  
> > @@ -293,11 +307,25 @@ static int input_action_end_x(struct sk_buff *skb, struct seg6_local_lwt *slwt)
> >  {
> >  	struct ipv6_sr_hdr *srh;
> >  
> > -	srh = get_and_validate_srh(skb);
> > +	srh = get_srh(skb);
> >  	if (!srh)
> >  		goto drop;
> >  
> > -	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +#ifdef CONFIG_IPV6_SEG6_HMAC
> > +	if (srh->segments_left > 0)
> > +		if (!seg6_hmac_validate_skb(skb))
> > +			goto drop;
> > +#endif
> > +
> > +	if (srh->segments_left == 0) {
> > +		if (!decap_and_validate(skb, srh->nexthdr))
> > +			goto drop;
> > +
> > +		if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
> > +			goto drop;
> > +	} else {
> > +		advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +	}
> >  
> >  	seg6_lookup_nexthop(skb, &slwt->nh6, 0);
> >  
> > @@ -312,11 +340,25 @@ static int input_action_end_t(struct sk_buff *skb, struct seg6_local_lwt *slwt)
> >  {
> >  	struct ipv6_sr_hdr *srh;
> >  
> > -	srh = get_and_validate_srh(skb);
> > +	srh = get_srh(skb);
> >  	if (!srh)
> >  		goto drop;
> >  
> > -	advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +#ifdef CONFIG_IPV6_SEG6_HMAC
> > +	if (srh->segments_left > 0)
> > +		if (!seg6_hmac_validate_skb(skb))
> > +			goto drop;
> > +#endif
> > +
> > +	if (srh->segments_left == 0) {
> > +		if (!decap_and_validate(skb, srh->nexthdr))
> > +			goto drop;
> > +
> > +		if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
> > +			goto drop;
> > +	} else {
> > +		advance_nextseg(srh, &ipv6_hdr(skb)->daddr);
> > +	}
> >  
> >  	seg6_lookup_nexthop(skb, NULL, slwt->table);
> >  
> > 
> 


-- 
Ahmed Abdelsalam <ahabdels.dev@...il.com>