icmp: ICMPV6: Examine invoking packet for Segment Route Headers.

RFC8754 says:

ICMP error packets generated within the SR domain are sent to source
nodes within the SR domain.  The invoking packet in the ICMP error
message may contain an SRH.  Since the destination address of a packet
with an SRH changes as each segment is processed, it may not be the
destination used by the socket or application that generated the
invoking packet.

For the source of an invoking packet to process the ICMP error
message, the ultimate destination address of the IPv6 header may be
required.  The following logic is used to determine the destination
address for use by protocol-error handlers.

*  Walk all extension headers of the invoking IPv6 packet to the
   routing extension header preceding the upper-layer header.

   -  If routing header is type 4 Segment Routing Header (SRH)

      o  The SID at Segment List[0] may be used as the destination
         address of the invoking packet.

Mangle the skb so the network header points to the invoking packet
inside the ICMP packet. The seg6 helpers can then be used on the skb
to find any segment routing headers. If found, mark this fact in the
IPv6 control block of the skb, and store the offset into the packet of
the SRH. Then restore the skb back to its old state.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: David Ahern <dsahern@kernel.org>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h
index 20c1f968da7c..a59d25f19385 100644
--- a/include/linux/ipv6.h
+++ b/include/linux/ipv6.h
@@ -133,6 +133,7 @@ struct inet6_skb_parm {
 	__u16			dsthao;
 #endif
 	__u16			frag_max_size;
+	__u16			srhoff;
 
 #define IP6SKB_XFRM_TRANSFORMED	1
 #define IP6SKB_FORWARDED	2
@@ -142,6 +143,7 @@ struct inet6_skb_parm {
 #define IP6SKB_HOPBYHOP        32
 #define IP6SKB_L3SLAVE         64
 #define IP6SKB_JUMBOGRAM      128
+#define IP6SKB_SEG6	      256
 };
 
 #if defined(CONFIG_NET_L3_MASTER_DEV)