[RFC PATCH 6/6] seg6: Add support to rearrange SRH for AH ICV calculation

[Tom Herbert <tom@herbertland.com>]

Mutable fields related to segment routing are: destination address,
segments left, and modifiable TLVs (those whose high order bit is set).

Add support to rearrange a segment routing (type 4) routing header to
handle these mutability requirements. This is described in
draft-herbert-ipv6-srh-ah-00.

Signed-off-by: Tom Herbert <tom@quantonium.net>
---
 net/ipv6/ah6.c | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/net/ipv6/ah6.c b/net/ipv6/ah6.c
index 032491c..0c5ca29 100644
--- a/net/ipv6/ah6.c
+++ b/net/ipv6/ah6.c
@@ -27,6 +27,7 @@
 #include <net/icmp.h>
 #include <net/ipv6.h>
 #include <net/protocol.h>
+#include <net/seg6.h>
 #include <net/xfrm.h>
 
 #define IPV6HDR_BASELEN 8
@@ -141,6 +142,13 @@ static bool zero_out_mutable_opts(struct ipv6_opt_hdr *opthdr)
 	return __zero_out_mutable_opts(opthdr, 2, 0x20, IPV6_TLV_PAD1);
 }
 
+static bool zero_out_mutable_srh_opts(struct ipv6_sr_hdr *srh)
+{
+	return __zero_out_mutable_opts((struct ipv6_opt_hdr *)srh,
+				       seg6_tlv_offset(srh), 0x80,
+				       SR6_TLV_PAD1);
+}
+
 #if IS_ENABLED(CONFIG_IPV6_MIP6)
 /**
  *	ipv6_rearrange_destopt - rearrange IPv6 destination options header
@@ -243,6 +251,20 @@ static bool ipv6_rearrange_type0_rthdr(struct ipv6hdr *iph,
 	return true;
 }
 
+static bool ipv6_rearrange_type4_rthdr(struct ipv6hdr *iph,
+				       struct ipv6_rt_hdr *rthdr)
+{
+	struct ipv6_sr_hdr *srh = (struct ipv6_sr_hdr *)rthdr;
+
+	if (!zero_out_mutable_srh_opts(srh))
+		return false;
+
+	rthdr->segments_left = 0;
+	iph->daddr = srh->segments[0];
+
+	return true;
+}
+
 static bool ipv6_rearrange_rthdr(struct ipv6hdr *iph, struct ipv6_rt_hdr *rthdr)
 {
 	switch (rthdr->type) {
@@ -251,6 +273,8 @@ static bool ipv6_rearrange_rthdr(struct ipv6hdr *iph, struct ipv6_rt_hdr *rthdr)
 		/* fallthrough */
 	case IPV6_SRCRT_TYPE_0: /* Deprecated */
 		return ipv6_rearrange_type0_rthdr(iph, rthdr);
+	case IPV6_SRCRT_TYPE_4:
+		return ipv6_rearrange_type4_rthdr(iph, rthdr);
 	default:
 		/* Bad or unidentified routing header, we don't know how
 		 * to fix this header for security purposes. Return failure.
-- 
2.7.4