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Subject[net-next] netfilter: add segment routing header 'srh' match
Date
It allows matching packets based on Segment Routing Header
(SRH) information.
The implementation considers revision 7 of the SRH draft.
https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-07

Currently supported match options include:
(1) Next Header
(2) Hdr Ext Len
(3) Segments Left
(4) Last Entry
(5) Tag value of SRH

Signed-off-by: Ahmed Abdelsalam <amsalam20@gmail.com>
---
include/uapi/linux/netfilter_ipv6/ip6t_srh.h | 63 ++++++++++
net/ipv6/netfilter/Kconfig | 9 ++
net/ipv6/netfilter/Makefile | 1 +
net/ipv6/netfilter/ip6t_srh.c | 165 +++++++++++++++++++++++++++
4 files changed, 238 insertions(+)
create mode 100644 include/uapi/linux/netfilter_ipv6/ip6t_srh.h
create mode 100644 net/ipv6/netfilter/ip6t_srh.c

diff --git a/include/uapi/linux/netfilter_ipv6/ip6t_srh.h b/include/uapi/linux/netfilter_ipv6/ip6t_srh.h
new file mode 100644
index 0000000..1b5dbd8
--- /dev/null
+++ b/include/uapi/linux/netfilter_ipv6/ip6t_srh.h
@@ -0,0 +1,63 @@
+/**
+ * Definitions for Segment Routing Header 'srh' match
+ *
+ * Author:
+ * Ahmed Abdelsalam <amsalam20@gmail.com>
+ */
+
+#ifndef _IP6T_SRH_H
+#define _IP6T_SRH_H
+
+#include <linux/types.h>
+#include <linux/netfilter.h>
+
+/* Values for "mt_flags" field in struct ip6t_srh */
+#define IP6T_SRH_NEXTHDR 0x0001
+#define IP6T_SRH_LEN_EQ 0x0002
+#define IP6T_SRH_LEN_GT 0x0004
+#define IP6T_SRH_LEN_LT 0x0008
+#define IP6T_SRH_SEGS_EQ 0x0010
+#define IP6T_SRH_SEGS_GT 0x0020
+#define IP6T_SRH_SEGS_LT 0x0040
+#define IP6T_SRH_LAST_EQ 0x0080
+#define IP6T_SRH_LAST_GT 0x0100
+#define IP6T_SRH_LAST_LT 0x0200
+#define IP6T_SRH_TAG 0x0400
+#define IP6T_SRH_MASK 0x07FF
+
+/* Values for "mt_invflags" field in struct ip6t_srh */
+#define IP6T_SRH_INV_NEXTHDR 0x0001
+#define IP6T_SRH_INV_LEN_EQ 0x0002
+#define IP6T_SRH_INV_LEN_GT 0x0004
+#define IP6T_SRH_INV_LEN_LT 0x0008
+#define IP6T_SRH_INV_SEGS_EQ 0x0010
+#define IP6T_SRH_INV_SEGS_GT 0x0020
+#define IP6T_SRH_INV_SEGS_LT 0x0040
+#define IP6T_SRH_INV_LAST_EQ 0x0080
+#define IP6T_SRH_INV_LAST_GT 0x0100
+#define IP6T_SRH_INV_LAST_LT 0x0200
+#define IP6T_SRH_INV_TAG 0x0400
+#define IP6T_SRH_INV_MASK 0x07FF
+
+/**
+ * struct ip6t_srh - SRH match options
+ * @ next_hdr: Next header field of SRH
+ * @ hdr_len: Extension header length field of SRH
+ * @ segs_left: Segments left field of SRH
+ * @ last_entry: Last entry field of SRH
+ * @ tag: Tag field of SRH
+ * @ mt_flags: match options
+ * @ mt_invflags: Invert the sense of match options
+ */
+
+struct ip6t_srh {
+ __u8 next_hdr;
+ __u8 hdr_len;
+ __u8 segs_left;
+ __u8 last_entry;
+ __u16 tag;
+ __u16 mt_flags;
+ __u16 mt_invflags;
+};
+
+#endif /*_IP6T_SRH_H*/
diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index 6acb2ee..e1818eb 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -232,6 +232,15 @@ config IP6_NF_MATCH_RT

To compile it as a module, choose M here. If unsure, say N.

+config IP6_NF_MATCH_SRH
+ tristate '"srh" Segment Routing header match support'
+ depends on NETFILTER_ADVANCED
+ help
+ srh matching allows you to match packets based on the segment
+ routing header of the packet.
+
+ To compile it as a module, choose M here. If unsure, say N.
+
# The targets
config IP6_NF_TARGET_HL
tristate '"HL" hoplimit target support'
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index c6ee0cd..e0d51a9 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/net/ipv6/netfilter/Makefile
@@ -54,6 +54,7 @@ obj-$(CONFIG_IP6_NF_MATCH_MH) += ip6t_mh.o
obj-$(CONFIG_IP6_NF_MATCH_OPTS) += ip6t_hbh.o
obj-$(CONFIG_IP6_NF_MATCH_RPFILTER) += ip6t_rpfilter.o
obj-$(CONFIG_IP6_NF_MATCH_RT) += ip6t_rt.o
+obj-$(CONFIG_IP6_NF_MATCH_SRH) += ip6t_srh.o

# targets
obj-$(CONFIG_IP6_NF_TARGET_MASQUERADE) += ip6t_MASQUERADE.o
diff --git a/net/ipv6/netfilter/ip6t_srh.c b/net/ipv6/netfilter/ip6t_srh.c
new file mode 100644
index 0000000..75e41dc9
--- /dev/null
+++ b/net/ipv6/netfilter/ip6t_srh.c
@@ -0,0 +1,165 @@
+/*
+ * Kernel module to match Segment Routing Header (SRH) parameters.
+ *
+ * Author:
+ * Ahmed Abdelsalam <amsalam20@gmail.com>
+ *
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/ipv6.h>
+#include <linux/types.h>
+#include <net/ipv6.h>
+#include <net/seg6.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter_ipv6/ip6t_srh.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Xtables: IPv6 Segment Routing Header match");
+MODULE_AUTHOR("Ahmed Abdelsalam <amsalam20@gmail.com>");
+
+/* Test a struct->mt_invflags and a boolean for inequality */
+#define NF_SRH_INVF(ptr, flag, boolean) \
+ ((boolean) ^ !!((ptr)->mt_invflags & (flag)))
+
+static bool srh_mt6(const struct sk_buff *skb, struct xt_action_param *par)
+{
+ const struct ip6t_srh *srhinfo = par->matchinfo;
+ struct ipv6_sr_hdr *srh;
+ struct ipv6_sr_hdr _srh;
+ int hdrlen, srhoff = 0;
+
+ 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;
+ return true;
+}
+
+static int srh_mt6_check(const struct xt_mtchk_param *par)
+{
+ const struct ip6t_srh *srhinfo = par->matchinfo;
+
+ if (srhinfo->mt_flags & ~IP6T_SRH_MASK) {
+ pr_debug("unknown srh match flags %X\n", srhinfo->mt_flags);
+ return -EINVAL;
+ }
+
+ if (srhinfo->mt_invflags & ~IP6T_SRH_INV_MASK) {
+ pr_debug("unknown srh invflags %X\n", srhinfo->mt_invflags);
+ return -EINVAL;
+ }
+
+ 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 __init srh_mt6_init(void)
+{
+ return xt_register_match(&srh_mt6_reg);
+}
+
+static void __exit srh_mt6_exit(void)
+{
+ xt_unregister_match(&srh_mt6_reg);
+}
+
+module_init(srh_mt6_init);
+module_exit(srh_mt6_exit);
--
2.1.4
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