seg6: ignore routing header with segments left equal to 0

When there are 2 segments routing header, after an End.B6 action
for example, the second SRH will never be handled by an action, packet will
be dropped when the first SRH has segments left equal to 0.
For actions that doesn't perform decapsulation (currently: End, End.X,
End.T, End.B6, End.B6.Encaps), this patch adds the IP6_FH_F_SKIP_RH flag
in arguments for ipv6_find_hdr().
Signed-off-by: Julien Massonneau <julien.massonneau@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/seg6_local.c

@@ -119,12 +119,12 @@ static struct seg6_local_lwt *seg6_local_lwtunnel(struct lwtunnel_state *lwt)
 	return (struct seg6_local_lwt *)lwt->data;
 }
 
-static struct ipv6_sr_hdr *get_srh(struct sk_buff *skb)
+static struct ipv6_sr_hdr *get_srh(struct sk_buff *skb, int flags)
 {
 	struct ipv6_sr_hdr *srh;
 	int len, srhoff = 0;
 
-	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)
+	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, &flags) < 0)
 		return NULL;
 
 	if (!pskb_may_pull(skb, srhoff + sizeof(*srh)))
@@ -152,13 +152,10 @@ static struct ipv6_sr_hdr *get_and_validate_srh(struct sk_buff *skb)
 {
 	struct ipv6_sr_hdr *srh;
 
-	srh = get_srh(skb);
+	srh = get_srh(skb, IP6_FH_F_SKIP_RH);
 	if (!srh)
 		return NULL;
 
-	if (srh->segments_left == 0)
-		return NULL;
-
 #ifdef CONFIG_IPV6_SEG6_HMAC
 	if (!seg6_hmac_validate_skb(skb))
 		return NULL;
@@ -172,7 +169,7 @@ static bool decap_and_validate(struct sk_buff *skb, int proto)
 	struct ipv6_sr_hdr *srh;
 	unsigned int off = 0;
 
-	srh = get_srh(skb);
+	srh = get_srh(skb, 0);
 	if (srh && srh->segments_left > 0)
 		return false;