netfilter: add xt_hmark target for hash-based skb marking

The target allows you to create rules in the "raw" and "mangle" tables
which set the skbuff mark by means of hash calculation within a given
range. The nfmark can influence the routing method (see "Use netfilter
MARK value as routing key") and can also be used by other subsystems to
change their behaviour.

[ Part of this patch has been refactorized and modified by Pablo Neira Ayuso ]

Signed-off-by: Hans Schillstrom <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter/xt_HMARK.h

···
+#ifndef XT_HMARK_H_
+#define XT_HMARK_H_
+
+#include <linux/types.h>
+
+enum {
+	XT_HMARK_SADDR_MASK,
+	XT_HMARK_DADDR_MASK,
+	XT_HMARK_SPI,
+	XT_HMARK_SPI_MASK,
+	XT_HMARK_SPORT,
+	XT_HMARK_DPORT,
+	XT_HMARK_SPORT_MASK,
+	XT_HMARK_DPORT_MASK,
+	XT_HMARK_PROTO_MASK,
+	XT_HMARK_RND,
+	XT_HMARK_MODULUS,
+	XT_HMARK_OFFSET,
+	XT_HMARK_CT,
+	XT_HMARK_METHOD_L3,
+	XT_HMARK_METHOD_L3_4,
+};
+#define XT_HMARK_FLAG(flag)	(1 << flag)
+
+union hmark_ports {
+	struct {
+		__u16	src;
+		__u16	dst;
+	} p16;
+	__u32	v32;
+};
+
+struct xt_hmark_info {
+	union nf_inet_addr	src_mask;
+	union nf_inet_addr	dst_mask;
+	union hmark_ports	port_mask;
+	union hmark_ports	port_set;
+	__u32			flags;
+	__u16			proto_mask;
+	__u32			hashrnd;
+	__u32			hmodulus;
+	__u32			hoffset;	/* Mark offset to start from */
+};
+
+#endif /* XT_HMARK_H_ */

net/netfilter/Kconfig

···
 	since you can easily create immortal packets that loop
 	forever on the network.
 
+config NETFILTER_XT_TARGET_HMARK
+	tristate '"HMARK" target support'
+	depends on (IP6_NF_IPTABLES || IP6_NF_IPTABLES=n)
+	depends on NETFILTER_ADVANCED
+	---help---
+	This option adds the "HMARK" target.
+
+	The target allows you to create rules in the "raw" and "mangle" tables
+	which set the skbuff mark by means of hash calculation within a given
+	range. The nfmark can influence the routing method (see "Use netfilter
+	MARK value as routing key") and can also be used by other subsystems to
+	change their behaviour.
+
+	To compile it as a module, choose M here. If unsure, say N.
+
 config NETFILTER_XT_TARGET_IDLETIMER
 	tristate  "IDLETIMER target support"
 	depends on NETFILTER_ADVANCED

net/netfilter/Makefile

···
 obj-$(CONFIG_NETFILTER_XT_TARGET_CT) += xt_CT.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_DSCP) += xt_DSCP.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_HL) += xt_HL.o
+obj-$(CONFIG_NETFILTER_XT_TARGET_HMARK) += xt_HMARK.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_LED) += xt_LED.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_LOG) += xt_LOG.o
 obj-$(CONFIG_NETFILTER_XT_TARGET_NFLOG) += xt_NFLOG.o

net/netfilter/xt_HMARK.c

···
+/*
+ * xt_HMARK - Netfilter module to set mark by means of hashing
+ *
+ * (C) 2012 by Hans Schillstrom <[e-mail]>
+ * (C) 2012 by Pablo Neira Ayuso <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published by
+ * the Free Software Foundation.
+ */
+
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/icmp.h>
+
+#include <linux/netfilter/x_tables.h>
+#include <linux/netfilter/xt_HMARK.h>
+
+#include <net/ip.h>
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+#include <net/netfilter/nf_conntrack.h>
+#endif
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+#include <net/ipv6.h>
+#include <linux/netfilter_ipv6/ip6_tables.h>
+#endif
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Hans Schillstrom <[e-mail]>");
+MODULE_DESCRIPTION("Xtables: packet marking using hash calculation");
+MODULE_ALIAS("ipt_HMARK");
+MODULE_ALIAS("ip6t_HMARK");
+
+struct hmark_tuple {
+	u32			src;
+	u32			dst;
+	union hmark_ports	uports;
+	uint8_t			proto;
+};
+
+static inline u32 hmark_addr6_mask(const __u32 *addr32, const __u32 *mask)
+{
+	return (addr32[0] & mask[0]) ^
+	       (addr32[1] & mask[1]) ^
+	       (addr32[2] & mask[2]) ^
+	       (addr32[3] & mask[3]);
+}
+
+static inline u32
+hmark_addr_mask(int l3num, const __u32 *addr32, const __u32 *mask)
+{
+	switch (l3num) {
+	case AF_INET:
+		return *addr32 & *mask;
+	case AF_INET6:
+		return hmark_addr6_mask(addr32, mask);
+	}
+	return 0;
+}
+
+static int
+hmark_ct_set_htuple(const struct sk_buff *skb, struct hmark_tuple *t,
+		    const struct xt_hmark_info *info)
+{
+#if IS_ENABLED(CONFIG_NF_CONNTRACK)
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
+	struct nf_conntrack_tuple *otuple;
+	struct nf_conntrack_tuple *rtuple;
+
+	if (ct == NULL || nf_ct_is_untracked(ct))
+		return -1;
+
+	otuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
+	rtuple = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
+
+	t->src = hmark_addr_mask(otuple->src.l3num, otuple->src.u3.all,
+				 info->src_mask.all);
+	t->dst = hmark_addr_mask(otuple->src.l3num, rtuple->src.u3.all,
+				 info->dst_mask.all);
+
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_METHOD_L3))
+		return 0;
+
+	t->proto = nf_ct_protonum(ct);
+	if (t->proto != IPPROTO_ICMP) {
+		t->uports.p16.src = otuple->src.u.all;
+		t->uports.p16.dst = rtuple->src.u.all;
+		t->uports.v32 = (t->uports.v32 & info->port_mask.v32) |
+				info->port_set.v32;
+		if (t->uports.p16.dst < t->uports.p16.src)
+			swap(t->uports.p16.dst, t->uports.p16.src);
+	}
+
+	return 0;
+#else
+	return -1;
+#endif
+}
+
+static inline u32
+hmark_hash(struct hmark_tuple *t, const struct xt_hmark_info *info)
+{
+	u32 hash;
+
+	if (t->dst < t->src)
+		swap(t->src, t->dst);
+
+	hash = jhash_3words(t->src, t->dst, t->uports.v32, info->hashrnd);
+	hash = hash ^ (t->proto & info->proto_mask);
+
+	return (hash % info->hmodulus) + info->hoffset;
+}
+
+static void
+hmark_set_tuple_ports(const struct sk_buff *skb, unsigned int nhoff,
+		      struct hmark_tuple *t, const struct xt_hmark_info *info)
+{
+	int protoff;
+
+	protoff = proto_ports_offset(t->proto);
+	if (protoff < 0)
+		return;
+
+	nhoff += protoff;
+	if (skb_copy_bits(skb, nhoff, &t->uports, sizeof(t->uports)) < 0)
+		return;
+
+	t->uports.v32 = (t->uports.v32 & info->port_mask.v32) |
+			info->port_set.v32;
+
+	if (t->uports.p16.dst < t->uports.p16.src)
+		swap(t->uports.p16.dst, t->uports.p16.src);
+}
+
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+static int get_inner6_hdr(const struct sk_buff *skb, int *offset)
+{
+	struct icmp6hdr *icmp6h, _ih6;
+
+	icmp6h = skb_header_pointer(skb, *offset, sizeof(_ih6), &_ih6);
+	if (icmp6h == NULL)
+		return 0;
+
+	if (icmp6h->icmp6_type && icmp6h->icmp6_type < 128) {
+		*offset += sizeof(struct icmp6hdr);
+		return 1;
+	}
+	return 0;
+}
+
+static int
+hmark_pkt_set_htuple_ipv6(const struct sk_buff *skb, struct hmark_tuple *t,
+			  const struct xt_hmark_info *info)
+{
+	struct ipv6hdr *ip6, _ip6;
+	int flag = IP6T_FH_F_AUTH;
+	unsigned int nhoff = 0;
+	u16 fragoff = 0;
+	int nexthdr;
+
+	ip6 = (struct ipv6hdr *) (skb->data + skb_network_offset(skb));
+	nexthdr = ipv6_find_hdr(skb, &nhoff, -1, &fragoff, &flag);
+	if (nexthdr < 0)
+		return 0;
+	/* No need to check for icmp errors on fragments */
+	if ((flag & IP6T_FH_F_FRAG) || (nexthdr != IPPROTO_ICMPV6))
+		goto noicmp;
+	/* Use inner header in case of ICMP errors */
+	if (get_inner6_hdr(skb, &nhoff)) {
+		ip6 = skb_header_pointer(skb, nhoff, sizeof(_ip6), &_ip6);
+		if (ip6 == NULL)
+			return -1;
+		/* If AH present, use SPI like in ESP. */
+		flag = IP6T_FH_F_AUTH;
+		nexthdr = ipv6_find_hdr(skb, &nhoff, -1, &fragoff, &flag);
+		if (nexthdr < 0)
+			return -1;
+	}
+noicmp:
+	t->src = hmark_addr6_mask(ip6->saddr.s6_addr32, info->src_mask.all);
+	t->dst = hmark_addr6_mask(ip6->daddr.s6_addr32, info->dst_mask.all);
+
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_METHOD_L3))
+		return 0;
+
+	t->proto = nexthdr;
+	if (t->proto == IPPROTO_ICMPV6)
+		return 0;
+
+	if (flag & IP6T_FH_F_FRAG)
+		return 0;
+
+	hmark_set_tuple_ports(skb, nhoff, t, info);
+	return 0;
+}
+
+static unsigned int
+hmark_tg_v6(struct sk_buff *skb, const struct xt_action_param *par)
+{
+	const struct xt_hmark_info *info = par->targinfo;
+	struct hmark_tuple t;
+
+	memset(&t, 0, sizeof(struct hmark_tuple));
+
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_CT)) {
+		if (hmark_ct_set_htuple(skb, &t, info) < 0)
+			return XT_CONTINUE;
+	} else {
+		if (hmark_pkt_set_htuple_ipv6(skb, &t, info) < 0)
+			return XT_CONTINUE;
+	}
+
+	skb->mark = hmark_hash(&t, info);
+	return XT_CONTINUE;
+}
+#endif
+
+static int get_inner_hdr(const struct sk_buff *skb, int iphsz, int *nhoff)
+{
+	const struct icmphdr *icmph;
+	struct icmphdr _ih;
+
+	/* Not enough header? */
+	icmph = skb_header_pointer(skb, *nhoff + iphsz, sizeof(_ih), &_ih);
+	if (icmph == NULL && icmph->type > NR_ICMP_TYPES)
+		return 0;
+
+	/* Error message? */
+	if (icmph->type != ICMP_DEST_UNREACH &&
+	    icmph->type != ICMP_SOURCE_QUENCH &&
+	    icmph->type != ICMP_TIME_EXCEEDED &&
+	    icmph->type != ICMP_PARAMETERPROB &&
+	    icmph->type != ICMP_REDIRECT)
+		return 0;
+
+	*nhoff += iphsz + sizeof(_ih);
+	return 1;
+}
+
+static int
+hmark_pkt_set_htuple_ipv4(const struct sk_buff *skb, struct hmark_tuple *t,
+			  const struct xt_hmark_info *info)
+{
+	struct iphdr *ip, _ip;
+	int nhoff = skb_network_offset(skb);
+
+	ip = (struct iphdr *) (skb->data + nhoff);
+	if (ip->protocol == IPPROTO_ICMP) {
+		/* Use inner header in case of ICMP errors */
+		if (get_inner_hdr(skb, ip->ihl * 4, &nhoff)) {
+			ip = skb_header_pointer(skb, nhoff, sizeof(_ip), &_ip);
+			if (ip == NULL)
+				return -1;
+		}
+	}
+
+	t->src = (__force u32) ip->saddr;
+	t->dst = (__force u32) ip->daddr;
+
+	t->src &= info->src_mask.ip;
+	t->dst &= info->dst_mask.ip;
+
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_METHOD_L3))
+		return 0;
+
+	t->proto = ip->protocol;
+
+	/* ICMP has no ports, skip */
+	if (t->proto == IPPROTO_ICMP)
+		return 0;
+
+	/* follow-up fragments don't contain ports, skip all fragments */
+	if (ip->frag_off & htons(IP_MF | IP_OFFSET))
+		return 0;
+
+	hmark_set_tuple_ports(skb, (ip->ihl * 4) + nhoff, t, info);
+
+	return 0;
+}
+
+static unsigned int
+hmark_tg_v4(struct sk_buff *skb, const struct xt_action_param *par)
+{
+	const struct xt_hmark_info *info = par->targinfo;
+	struct hmark_tuple t;
+
+	memset(&t, 0, sizeof(struct hmark_tuple));
+
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_CT)) {
+		if (hmark_ct_set_htuple(skb, &t, info) < 0)
+			return XT_CONTINUE;
+	} else {
+		if (hmark_pkt_set_htuple_ipv4(skb, &t, info) < 0)
+			return XT_CONTINUE;
+	}
+
+	skb->mark = hmark_hash(&t, info);
+	return XT_CONTINUE;
+}
+
+static int hmark_tg_check(const struct xt_tgchk_param *par)
+{
+	const struct xt_hmark_info *info = par->targinfo;
+
+	if (!info->hmodulus) {
+		pr_info("xt_HMARK: hash modulus can't be zero\n");
+		return -EINVAL;
+	}
+	if (info->proto_mask &&
+	    (info->flags & XT_HMARK_FLAG(XT_HMARK_METHOD_L3))) {
+		pr_info("xt_HMARK: proto mask must be zero with L3 mode\n");
+		return -EINVAL;
+	}
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_SPI_MASK) &&
+	    (info->flags & (XT_HMARK_FLAG(XT_HMARK_SPORT_MASK) |
+			     XT_HMARK_FLAG(XT_HMARK_DPORT_MASK)))) {
+		pr_info("xt_HMARK: spi-mask and port-mask can't be combined\n");
+		return -EINVAL;
+	}
+	if (info->flags & XT_HMARK_FLAG(XT_HMARK_SPI) &&
+	    (info->flags & (XT_HMARK_FLAG(XT_HMARK_SPORT) |
+			     XT_HMARK_FLAG(XT_HMARK_DPORT)))) {
+		pr_info("xt_HMARK: spi-set and port-set can't be combined\n");
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static struct xt_target hmark_tg_reg[] __read_mostly = {
+	{
+		.name		= "HMARK",
+		.family		= NFPROTO_IPV4,
+		.target		= hmark_tg_v4,
+		.targetsize	= sizeof(struct xt_hmark_info),
+		.checkentry	= hmark_tg_check,
+		.me		= THIS_MODULE,
+	},
+#if IS_ENABLED(CONFIG_IP6_NF_IPTABLES)
+	{
+		.name		= "HMARK",
+		.family		= NFPROTO_IPV6,
+		.target		= hmark_tg_v6,
+		.targetsize	= sizeof(struct xt_hmark_info),
+		.checkentry	= hmark_tg_check,
+		.me		= THIS_MODULE,
+	},
+#endif
+};
+
+static int __init hmark_tg_init(void)
+{
+	return xt_register_targets(hmark_tg_reg, ARRAY_SIZE(hmark_tg_reg));
+}
+
+static void __exit hmark_tg_exit(void)
+{
+	xt_unregister_targets(hmark_tg_reg, ARRAY_SIZE(hmark_tg_reg));
+}
+
+module_init(hmark_tg_init);
+module_exit(hmark_tg_exit);