netfilter: ip6t_srh: extend SRH matching for previous, next and last SID

IPv6 Segment Routing Header (SRH) contains a list of SIDs to be crossed
by SR encapsulated packet. Each SID is encoded as an IPv6 prefix.

When a Firewall receives an SR encapsulated packet, it should be able
to identify which node previously processed the packet (previous SID),
which node is going to process the packet next (next SID), and which
node is the last to process the packet (last SID) which represent the
final destination of the packet in case of inline SR mode.

An example use-case of using these features could be SID list that
includes two firewalls. When the second firewall receives a packet,
it can check whether the packet has been processed by the first firewall
or not. Based on that check, it decides to apply all rules, apply just
subset of the rules, or totally skip all rules and forward the packet to
the next SID.

This patch extends SRH match to support matching previous SID, next SID,
and last SID.

Signed-off-by: Ahmed Abdelsalam <amsalam20@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 164 insertions, 9 deletions

diff --git a/net/ipv6/netfilter/ip6t_srh.c b/net/ipv6/netfilter/ip6t_srh.c
index 33719d5560c8..1059894a6f4c 100644
--- a/net/ipv6/netfilter/ip6t_srh.c
+++ b/net/ipv6/netfilter/ip6t_srh.c
@@ -117,6 +117,130 @@ static bool srh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
 	return true;
 }
 
+static bool srh1_mt6(const struct sk_buff *skb, struct xt_action_param *par)
+{
+	int hdrlen, psidoff, nsidoff, lsidoff, srhoff = 0;
+	const struct ip6t_srh1 *srhinfo = par->matchinfo;
+	struct in6_addr *psid, *nsid, *lsid;
+	struct in6_addr _psid, _nsid, _lsid;
+	struct ipv6_sr_hdr *srh;
+	struct ipv6_sr_hdr _srh;
+
+	if (ipv6_find_hdr(skb, &srhoff, IPPROTO_ROUTING, NULL, NULL) < 0)
+		return false;
+	srh = skb_header_pointer(skb, srhoff, sizeof(_srh), &_srh);
+	if (!srh)
+		return false;
+
+	hdrlen = ipv6_optlen(srh);
+	if (skb->len - srhoff < hdrlen)
+		return false;
+
+	if (srh->type != IPV6_SRCRT_TYPE_4)
+		return false;
+
+	if (srh->segments_left > srh->first_segment)
+		return false;
+
+	/* Next Header matching */
+	if (srhinfo->mt_flags & IP6T_SRH_NEXTHDR)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_NEXTHDR,
+				!(srh->nexthdr == srhinfo->next_hdr)))
+			return false;
+
+	/* Header Extension Length matching */
+	if (srhinfo->mt_flags & IP6T_SRH_LEN_EQ)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LEN_EQ,
+				!(srh->hdrlen == srhinfo->hdr_len)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_LEN_GT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LEN_GT,
+				!(srh->hdrlen > srhinfo->hdr_len)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_LEN_LT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LEN_LT,
+				!(srh->hdrlen < srhinfo->hdr_len)))
+			return false;
+
+	/* Segments Left matching */
+	if (srhinfo->mt_flags & IP6T_SRH_SEGS_EQ)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_SEGS_EQ,
+				!(srh->segments_left == srhinfo->segs_left)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_SEGS_GT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_SEGS_GT,
+				!(srh->segments_left > srhinfo->segs_left)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_SEGS_LT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_SEGS_LT,
+				!(srh->segments_left < srhinfo->segs_left)))
+			return false;
+
+	/**
+	 * Last Entry matching
+	 * Last_Entry field was introduced in revision 6 of the SRH draft.
+	 * It was called First_Segment in the previous revision
+	 */
+	if (srhinfo->mt_flags & IP6T_SRH_LAST_EQ)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LAST_EQ,
+				!(srh->first_segment == srhinfo->last_entry)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_LAST_GT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LAST_GT,
+				!(srh->first_segment > srhinfo->last_entry)))
+			return false;
+	if (srhinfo->mt_flags & IP6T_SRH_LAST_LT)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LAST_LT,
+				!(srh->first_segment < srhinfo->last_entry)))
+			return false;
+
+	/**
+	 * Tag matchig
+	 * Tag field was introduced in revision 6 of the SRH draft
+	 */
+	if (srhinfo->mt_flags & IP6T_SRH_TAG)
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_TAG,
+				!(srh->tag == srhinfo->tag)))
+			return false;
+
+	/* Previous SID matching */
+	if (srhinfo->mt_flags & IP6T_SRH_PSID) {
+		if (srh->segments_left == srh->first_segment)
+			return false;
+		psidoff = srhoff + sizeof(struct ipv6_sr_hdr) +
+			  ((srh->segments_left + 1) * sizeof(struct in6_addr));
+		psid = skb_header_pointer(skb, psidoff, sizeof(_psid), &_psid);
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_PSID,
+				ipv6_masked_addr_cmp(psid, &srhinfo->psid_msk,
+						     &srhinfo->psid_addr)))
+			return false;
+	}
+
+	/* Next SID matching */
+	if (srhinfo->mt_flags & IP6T_SRH_NSID) {
+		if (srh->segments_left == 0)
+			return false;
+		nsidoff = srhoff + sizeof(struct ipv6_sr_hdr) +
+			  ((srh->segments_left - 1) * sizeof(struct in6_addr));
+		nsid = skb_header_pointer(skb, nsidoff, sizeof(_nsid), &_nsid);
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_NSID,
+				ipv6_masked_addr_cmp(nsid, &srhinfo->nsid_msk,
+						     &srhinfo->nsid_addr)))
+			return false;
+	}
+
+	/* Last SID matching */
+	if (srhinfo->mt_flags & IP6T_SRH_LSID) {
+		lsidoff = srhoff + sizeof(struct ipv6_sr_hdr);
+		lsid = skb_header_pointer(skb, lsidoff, sizeof(_lsid), &_lsid);
+		if (NF_SRH_INVF(srhinfo, IP6T_SRH_INV_LSID,
+				ipv6_masked_addr_cmp(lsid, &srhinfo->lsid_msk,
+						     &srhinfo->lsid_addr)))
+			return false;
+	}
+	return true;
+}
+
 static int srh_mt6_check(const struct xt_mtchk_param *par)
 {
 	const struct ip6t_srh *srhinfo = par->matchinfo;
@@ -136,23 +260,54 @@ static int srh_mt6_check(const struct xt_mtchk_param *par)
 	return 0;
 }
 
-static struct xt_match srh_mt6_reg __read_mostly = {
-	.name		= "srh",
-	.family		= NFPROTO_IPV6,
-	.match		= srh_mt6,
-	.matchsize	= sizeof(struct ip6t_srh),
-	.checkentry	= srh_mt6_check,
-	.me		= THIS_MODULE,
+static int srh1_mt6_check(const struct xt_mtchk_param *par)
+{
+	const struct ip6t_srh1 *srhinfo = par->matchinfo;
+
+	if (srhinfo->mt_flags & ~IP6T_SRH_MASK) {
+		pr_info_ratelimited("unknown srh match flags  %X\n",
+				    srhinfo->mt_flags);
+		return -EINVAL;
+	}
+
+	if (srhinfo->mt_invflags & ~IP6T_SRH_INV_MASK) {
+		pr_info_ratelimited("unknown srh invflags %X\n",
+				    srhinfo->mt_invflags);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static struct xt_match srh_mt6_reg[] __read_mostly = {
+	{
+		.name		= "srh",
+		.revision	= 0,
+		.family		= NFPROTO_IPV6,
+		.match		= srh_mt6,
+		.matchsize	= sizeof(struct ip6t_srh),
+		.checkentry	= srh_mt6_check,
+		.me		= THIS_MODULE,
+	},
+	{
+		.name           = "srh",
+		.revision       = 1,
+		.family         = NFPROTO_IPV6,
+		.match          = srh1_mt6,
+		.matchsize      = sizeof(struct ip6t_srh1),
+		.checkentry     = srh1_mt6_check,
+		.me             = THIS_MODULE,
+	}
 };
 
 static int __init srh_mt6_init(void)
 {
-	return xt_register_match(&srh_mt6_reg);
+	return xt_register_matches(srh_mt6_reg, ARRAY_SIZE(srh_mt6_reg));
 }
 
 static void __exit srh_mt6_exit(void)
 {
-	xt_unregister_match(&srh_mt6_reg);
+	xt_unregister_matches(srh_mt6_reg, ARRAY_SIZE(srh_mt6_reg));
 }
 
 module_init(srh_mt6_init);