xfrm: ipv6: move mip6_destopt_offset into xfrm core

This helper is relatively small, just move this to the xfrm core
and call it directly.

Next patch does the same for the ROUTING type.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 6b44b6e738f7..29959054a535 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -77,8 +77,65 @@ static int xfrm4_transport_output(struct xfrm_state *x, struct sk_buff *skb)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_IPV6_MIP6)
+static int mip6_destopt_offset(struct xfrm_state *x, struct sk_buff *skb,
+			       u8 **nexthdr)
+{
+	u16 offset = sizeof(struct ipv6hdr);
+	struct ipv6_opt_hdr *exthdr =
+				   (struct ipv6_opt_hdr *)(ipv6_hdr(skb) + 1);
+	const unsigned char *nh = skb_network_header(skb);
+	unsigned int packet_len = skb_tail_pointer(skb) -
+		skb_network_header(skb);
+	int found_rhdr = 0;
+
+	*nexthdr = &ipv6_hdr(skb)->nexthdr;
+
+	while (offset + 1 <= packet_len) {
+		switch (**nexthdr) {
+		case NEXTHDR_HOP:
+			break;
+		case NEXTHDR_ROUTING:
+			found_rhdr = 1;
+			break;
+		case NEXTHDR_DEST:
+			/* HAO MUST NOT appear more than once.
+			 * XXX: It is better to try to find by the end of
+			 * XXX: packet if HAO exists.
+			 */
+			if (ipv6_find_tlv(skb, offset, IPV6_TLV_HAO) >= 0) {
+				net_dbg_ratelimited("mip6: hao exists already, override\n");
+				return offset;
+			}
+
+			if (found_rhdr)
+				return offset;
+
+			break;
+		default:
+			return offset;
+		}
+
+		offset += ipv6_optlen(exthdr);
+		*nexthdr = &exthdr->nexthdr;
+		exthdr = (struct ipv6_opt_hdr *)(nh + offset);
+	}
+
+	return offset;
+}
+#endif
+
 static int xfrm6_hdr_offset(struct xfrm_state *x, struct sk_buff *skb, u8 **prevhdr)
 {
+	switch (x->type->proto) {
+#if IS_ENABLED(CONFIG_IPV6_MIP6)
+	case IPPROTO_DSTOPTS:
+		return mip6_destopt_offset(x, skb, prevhdr);
+#endif
+	default:
+		break;
+	}
+
 	return x->type->hdr_offset(x, skb, prevhdr);
 }