seg6: export get_srh() for ICMP handling

An ICMP error message can contain in its message body part of an IPv6
packet which invoked the error. Such a packet might contain a segment
router header. Export get_srh() so the ICMP code can make use of it.

Since his changes the scope of the function from local to global, add
the seg6_ prefix to keep the namespace clean. And move it into seg6.c
so it is always available, not just when IPV6_SEG6_LWTUNNEL is
enabled.

Signed-off-by: Andrew Lunn <[e-mail]>
Reviewed-by: David Ahern <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/seg6.h

···
 extern void seg6_local_exit(void);
 
 extern bool seg6_validate_srh(struct ipv6_sr_hdr *srh, int len, bool reduced);
+extern struct ipv6_sr_hdr *seg6_get_srh(struct sk_buff *skb, int flags);
 extern int seg6_do_srh_encap(struct sk_buff *skb, struct ipv6_sr_hdr *osrh,
 			     int proto);
 extern int seg6_do_srh_inline(struct sk_buff *skb, struct ipv6_sr_hdr *osrh);

net/ipv6/seg6.c

···
 	return true;
 }
 
+struct ipv6_sr_hdr *seg6_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, &flags) < 0)
+		return NULL;
+
+	if (!pskb_may_pull(skb, srhoff + sizeof(*srh)))
+		return NULL;
+
+	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
+
+	len = (srh->hdrlen + 1) << 3;
+
+	if (!pskb_may_pull(skb, srhoff + len))
+		return NULL;
+
+	/* note that pskb_may_pull may change pointers in header;
+	 * for this reason it is necessary to reload them when needed.
+	 */
+	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
+
+	if (!seg6_validate_srh(srh, len, true))
+		return NULL;
+
+	return srh;
+}
+
 static struct genl_family seg6_genl_family;
 
 static const struct nla_policy seg6_genl_policy[SEG6_ATTR_MAX + 1] = {

net/ipv6/seg6_local.c

···
 	return (struct seg6_local_lwt *)lwt->data;
 }
 
-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, &flags) < 0)
-		return NULL;
-
-	if (!pskb_may_pull(skb, srhoff + sizeof(*srh)))
-		return NULL;
-
-	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
-
-	len = (srh->hdrlen + 1) << 3;
-
-	if (!pskb_may_pull(skb, srhoff + len))
-		return NULL;
-
-	/* note that pskb_may_pull may change pointers in header;
-	 * for this reason it is necessary to reload them when needed.
-	 */
-	srh = (struct ipv6_sr_hdr *)(skb->data + srhoff);
-
-	if (!seg6_validate_srh(srh, len, true))
-		return NULL;
-
-	return srh;
-}
-
 static struct ipv6_sr_hdr *get_and_validate_srh(struct sk_buff *skb)
 {
 	struct ipv6_sr_hdr *srh;
 
-	srh = get_srh(skb, IP6_FH_F_SKIP_RH);
+	srh = seg6_get_srh(skb, IP6_FH_F_SKIP_RH);
 	if (!srh)
 		return NULL;
 
···
 	struct ipv6_sr_hdr *srh;
 	unsigned int off = 0;
 
-	srh = get_srh(skb, 0);
+	srh = seg6_get_srh(skb, 0);
 	if (srh && srh->segments_left > 0)
 		return false;