[IPV6] MIP6: Revert address to send ICMPv6 error.

IPv6 source address is replaced in receiving packet
with home address option carried by destination options header.
To send ICMPv6 error back, original address which is received one on wire
should be used. This function checks such header is included
and reverts them.
Based on MIPL2 kernel patch.

This patch was also written by: Ville Nuorvala <vnuorval@tcs.hut.fi>
Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/icmp.c

@@ -273,6 +273,29 @@ static int icmpv6_getfrag(void *from, char *to, int offset, int len, int odd, st
 	return 0;
 }
 
+#ifdef CONFIG_IPV6_MIP6
+static void mip6_addr_swap(struct sk_buff *skb)
+{
+	struct ipv6hdr *iph = skb->nh.ipv6h;
+	struct inet6_skb_parm *opt = IP6CB(skb);
+	struct ipv6_destopt_hao *hao;
+	struct in6_addr tmp;
+	int off;
+
+	if (opt->dsthao) {
+		off = ipv6_find_tlv(skb, opt->dsthao, IPV6_TLV_HAO);
+		if (likely(off >= 0)) {
+			hao = (struct ipv6_destopt_hao *)(skb->nh.raw + off);
+			ipv6_addr_copy(&tmp, &iph->saddr);
+			ipv6_addr_copy(&iph->saddr, &hao->addr);
+			ipv6_addr_copy(&hao->addr, &tmp);
+		}
+	}
+}
+#else
+static inline void mip6_addr_swap(struct sk_buff *skb) {}
+#endif
+
 /*
  *	Send an ICMP message in response to a packet in error
  */
@@ -350,6 +373,8 @@ void icmpv6_send(struct sk_buff *skb, int type, int code, __u32 info,
 		return;
 	}
 
+	mip6_addr_swap(skb);
+
 	memset(&fl, 0, sizeof(fl));
 	fl.proto = IPPROTO_ICMPV6;
 	ipv6_addr_copy(&fl.fl6_dst, &hdr->saddr);