[PATCH][EBTABLES] add "ebt_among" match

Hi Dave,

This patch adds the ebtables among target. This allows fast matching of
a frame's MAC src/dst address vs a list of addresses. It also allows
matching on MAC/IP address pairs, making it possible to put loads of
anti-spoofing entries inside one ebtables rule. This is a big speed
improvement.

The patch is from Grzegorz Borowiak <grzes_at_gnu.univ.gda.pl>

cheers,
Bart


--- linux-2.6.0-test6/net/bridge/netfilter/Kconfig.old	2003-10-12 16:04:03.000000000 +0200
+++ linux-2.6.0-test6/net/bridge/netfilter/Kconfig	2003-10-12 16:09:05.000000000 +0200
@@ -55,6 +55,16 @@ config BRIDGE_EBT_802_3
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config BRIDGE_EBT_AMONG
+	tristate "ebt: among filter support"
+	depends on BRIDGE_NF_EBTABLES
+	help
+	  This option adds the among match, which allows matching the MAC source
+	  and/or destination address on a list of addresses. Optionally,
+	  MAC/IP address pairs can be matched, f.e. for anti-spoofing rules.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config BRIDGE_EBT_ARP
 	tristate "ebt: ARP filter support"
 	depends on BRIDGE_NF_EBTABLES
--- linux-2.6.0-test6/net/bridge/netfilter/Makefile.old	2003-10-12 16:03:24.000000000 +0200
+++ linux-2.6.0-test6/net/bridge/netfilter/Makefile	2003-10-12 16:03:54.000000000 +0200
@@ -11,6 +11,7 @@ obj-$(CONFIG_BRIDGE_EBT_T_NAT) += ebtabl
 
 #matches
 obj-$(CONFIG_BRIDGE_EBT_802_3) += ebt_802_3.o
+obj-$(CONFIG_BRIDGE_EBT_AMONG) += ebt_among.o
 obj-$(CONFIG_BRIDGE_EBT_ARP) += ebt_arp.o
 obj-$(CONFIG_BRIDGE_EBT_IP) += ebt_ip.o
 obj-$(CONFIG_BRIDGE_EBT_MARK) += ebt_mark_m.o
--- /dev/null	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.0-test6/net/bridge/netfilter/ebt_among.c	2003-10-12 16:03:02.000000000 +0200
@@ -0,0 +1,215 @@
+/*
+ *  ebt_among
+ *
+ *	Authors:
+ *	Grzegorz Borowiak <[email protected]>
+ *
+ *  August, 2003
+ *
+ */
+
+#include <linux/netfilter_bridge/ebtables.h>
+#include <linux/netfilter_bridge/ebt_among.h>
+#include <linux/ip.h>
+#include <linux/if_arp.h>
+#include <linux/module.h>
+
+static int ebt_mac_wormhash_contains(const struct ebt_mac_wormhash *wh,
+				     const char *mac, uint32_t ip)
+{
+	/* You may be puzzled as to how this code works.
+	 * Some tricks were used, refer to 
+	 * 	include/linux/netfilter_bridge/ebt_among.h
+	 * as there you can find a solution of this mystery.
+	 */
+	const struct ebt_mac_wormhash_tuple *p;
+	int start, limit, i;
+	uint32_t cmp[2] = { 0, 0 };
+	int key = (const unsigned char) mac[5];
+
+	memcpy(((char *) cmp) + 2, mac, 6);
+	start = wh->table[key];
+	limit = wh->table[key + 1];
+	if (ip) {
+		for (i = start; i < limit; i++) {
+			p = &wh->pool[i];
+			if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0]) {
+				if (p->ip == 0 || p->ip == ip) {
+					return 1;
+				}
+			}
+		}
+	} else {
+		for (i = start; i < limit; i++) {
+			p = &wh->pool[i];
+			if (cmp[1] == p->cmp[1] && cmp[0] == p->cmp[0]) {
+				if (p->ip == 0) {
+					return 1;
+				}
+			}
+		}
+	}
+	return 0;
+}
+
+static int ebt_mac_wormhash_check_integrity(const struct ebt_mac_wormhash
+					    *wh)
+{
+	int i;
+
+	for (i = 0; i < 256; i++) {
+		if (wh->table[i] > wh->table[i + 1])
+			return -0x100 - i;
+		if (wh->table[i] < 0)
+			return -0x200 - i;
+		if (wh->table[i] > wh->poolsize)
+			return -0x300 - i;
+	}
+	if (wh->table[256] > wh->poolsize)
+		return -0xc00;
+	return 0;
+}
+
+static int get_ip_dst(const struct sk_buff *skb, uint32_t *addr)
+{
+	if (skb->mac.ethernet->h_proto == __constant_htons(ETH_P_IP)) {
+		struct iphdr iph;
+
+		if (skb_copy_bits(skb, 0, &iph, sizeof(iph)))
+			return -1;
+		*addr = iph.daddr;
+	} else if (skb->mac.ethernet->h_proto == __constant_htons(ETH_P_ARP)) {
+		struct arphdr arph;
+
+		if (skb_copy_bits(skb, 0, &arph, sizeof(arph)) ||
+		    arph.ar_pln != sizeof(uint32_t) || arph.ar_hln != ETH_ALEN)
+			return -1;
+		if (skb_copy_bits(skb, sizeof(struct arphdr) +
+		    2 * ETH_ALEN + sizeof(uint32_t), addr, sizeof(uint32_t)))
+			return -1;
+	}
+	return 0;
+}
+
+static int get_ip_src(const struct sk_buff *skb, uint32_t *addr)
+{
+	if (skb->mac.ethernet->h_proto == __constant_htons(ETH_P_IP)) {
+		struct iphdr iph;
+
+		if (skb_copy_bits(skb, 0, &iph, sizeof(iph)))
+			return -1;
+		*addr = iph.saddr;
+	} else if (skb->mac.ethernet->h_proto == __constant_htons(ETH_P_ARP)) {
+		struct arphdr arph;
+
+		if (skb_copy_bits(skb, 0, &arph, sizeof(arph)) ||
+		    arph.ar_pln != sizeof(uint32_t) || arph.ar_hln != ETH_ALEN)
+			return -1;
+		if (skb_copy_bits(skb, sizeof(struct arphdr) +
+		    ETH_ALEN, addr, sizeof(uint32_t)))
+			return -1;
+	}
+	return 0;
+}
+
+static int ebt_filter_among(const struct sk_buff *skb,
+			    const struct net_device *in,
+			    const struct net_device *out, const void *data,
+			    unsigned int datalen)
+{
+	struct ebt_among_info *info = (struct ebt_among_info *) data;
+	const char *dmac, *smac;
+	const struct ebt_mac_wormhash *wh_dst, *wh_src;
+	uint32_t dip = 0, sip = 0;
+
+	wh_dst = ebt_among_wh_dst(info);
+	wh_src = ebt_among_wh_src(info);
+
+	if (wh_src) {
+		smac = skb->mac.ethernet->h_source;
+		if (get_ip_src(skb, &sip))
+			return EBT_NOMATCH;
+		if (!(info->bitmask & EBT_AMONG_SRC_NEG)) {
+			/* we match only if it contains */
+			if (!ebt_mac_wormhash_contains(wh_src, smac, sip))
+				return EBT_NOMATCH;
+		} else {
+			/* we match only if it DOES NOT contain */
+			if (ebt_mac_wormhash_contains(wh_src, smac, sip))
+				return EBT_NOMATCH;
+		}
+	}
+
+	if (wh_dst) {
+		dmac = skb->mac.ethernet->h_dest;
+		if (get_ip_dst(skb, &dip))
+			return EBT_NOMATCH;
+		if (!(info->bitmask & EBT_AMONG_DST_NEG)) {
+			/* we match only if it contains */
+			if (!ebt_mac_wormhash_contains(wh_dst, dmac, dip))
+				return EBT_NOMATCH;
+		} else {
+			/* we match only if it DOES NOT contain */
+			if (ebt_mac_wormhash_contains(wh_dst, dmac, dip))
+				return EBT_NOMATCH;
+		}
+	}
+
+	return EBT_MATCH;
+}
+
+static int ebt_among_check(const char *tablename, unsigned int hookmask,
+			   const struct ebt_entry *e, void *data,
+			   unsigned int datalen)
+{
+	struct ebt_among_info *info = (struct ebt_among_info *) data;
+	int expected_length = sizeof(struct ebt_among_info);
+	const struct ebt_mac_wormhash *wh_dst, *wh_src;
+	int err;
+
+	wh_dst = ebt_among_wh_dst(info);
+	wh_src = ebt_among_wh_src(info);
+	expected_length += ebt_mac_wormhash_size(wh_dst);
+	expected_length += ebt_mac_wormhash_size(wh_src);
+
+	if (datalen != EBT_ALIGN(expected_length)) {
+		printk(KERN_WARNING
+		       "ebtables: among: wrong size: %d"
+		       "against expected %d, rounded to %d\n",
+		       datalen, expected_length,
+		       EBT_ALIGN(expected_length));
+		return -EINVAL;
+	}
+	if (wh_dst && (err = ebt_mac_wormhash_check_integrity(wh_dst))) {
+		printk(KERN_WARNING
+		       "ebtables: among: dst integrity fail: %x\n", -err);
+		return -EINVAL;
+	}
+	if (wh_src && (err = ebt_mac_wormhash_check_integrity(wh_src))) {
+		printk(KERN_WARNING
+		       "ebtables: among: src integrity fail: %x\n", -err);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static struct ebt_match filter_among = {
+	.name		= EBT_AMONG_MATCH, 
+	.match		= ebt_filter_among, 
+	.check		= ebt_among_check,
+	.me		= THIS_MODULE,
+};
+
+static int __init init(void)
+{
+	return ebt_register_match(&filter_among);
+}
+
+static void __exit fini(void)
+{
+	ebt_unregister_match(&filter_among);
+}
+
+module_init(init);
+module_exit(fini);
+MODULE_LICENSE("GPL");
--- /dev/null	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.0-test6/include/linux/netfilter_bridge/ebt_among.h	2003-10-12 16:02:51.000000000 +0200
@@ -0,0 +1,65 @@
+#ifndef __LINUX_BRIDGE_EBT_AMONG_H
+#define __LINUX_BRIDGE_EBT_AMONG_H
+
+#define EBT_AMONG_DST 0x01
+#define EBT_AMONG_SRC 0x02
+
+/* Grzegorz Borowiak <[email protected]> 2003
+ * 
+ * Write-once-read-many hash table, used for checking if a given
+ * MAC address belongs to a set or not and possibly for checking
+ * if it is related with a given IPv4 address.
+ *
+ * The hash value of an address is its last byte.
+ * 
+ * In real-world ethernet addresses, values of the last byte are
+ * evenly distributed and there is no need to consider other bytes.
+ * It would only slow the routines down.
+ *
+ * For MAC address comparison speedup reasons, we introduce a trick.
+ * MAC address is mapped onto an array of two 32-bit integers.
+ * This pair of integers is compared with MAC addresses in the
+ * hash table, which are stored also in form of pairs of integers
+ * (in `cmp' array). This is quick as it requires only two elementary
+ * number comparisons in worst case. Further, we take advantage of
+ * fact that entropy of 3 last bytes of address is larger than entropy
+ * of 3 first bytes. So first we compare 4 last bytes of addresses and
+ * if they are the same we compare 2 first.
+ *
+ * Yes, it is a memory overhead, but in 2003 AD, who cares?
+ */
+
+struct ebt_mac_wormhash_tuple
+{
+	uint32_t cmp[2];
+	uint32_t ip;
+};
+
+struct ebt_mac_wormhash
+{
+	int table[257];
+	int poolsize;
+	struct ebt_mac_wormhash_tuple pool[0];
+};
+
+#define ebt_mac_wormhash_size(x) ((x) ? sizeof(struct ebt_mac_wormhash) \
+		+ (x)->poolsize * sizeof(struct ebt_mac_wormhash_tuple) : 0)
+
+struct ebt_among_info
+{
+	int wh_dst_ofs;
+	int wh_src_ofs;
+	int bitmask;
+};
+
+#define EBT_AMONG_DST_NEG 0x1
+#define EBT_AMONG_SRC_NEG 0x2
+
+#define ebt_among_wh_dst(x) ((x)->wh_dst_ofs ? \
+	(struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_dst_ofs) : NULL)
+#define ebt_among_wh_src(x) ((x)->wh_src_ofs ? \
+	(struct ebt_mac_wormhash*)((char*)(x) + (x)->wh_src_ofs) : NULL)
+
+#define EBT_AMONG_MATCH "among"
+
+#endif



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