Move ipfw's nat code into its own kld: ipfw_nat.

1 files changed, 646 insertions, 0 deletions

diff --git a/sys/netinet/ip_fw_nat.c b/sys/netinet/ip_fw_nat.c
new file mode 100644
index 0000000..488fd86
--- /dev/null
+++ b/sys/netinet/ip_fw_nat.c
@@ -0,0 +1,646 @@
+/*-
+ * Copyright (c) 2008 Paolo Pisati
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/condvar.h>
+#include <sys/eventhandler.h>
+#include <sys/malloc.h>
+#include <sys/mbuf.h>
+#include <sys/kernel.h>
+#include <sys/lock.h>
+#include <sys/jail.h>
+#include <sys/module.h>
+#include <sys/priv.h>
+#include <sys/proc.h>
+#include <sys/rwlock.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+#include <sys/sysctl.h>
+#include <sys/syslog.h>
+#include <sys/ucred.h>
+
+#include <netinet/libalias/alias.h>
+#include <netinet/libalias/alias_local.h>
+
+#define	IPFW_INTERNAL	/* Access to protected data structures in ip_fw.h. */
+
+#include <net/if.h>
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/ip_var.h>
+#include <netinet/ip_icmp.h>
+#include <netinet/ip_fw.h>
+#include <netinet/tcp.h>
+#include <netinet/tcp_timer.h>
+#include <netinet/tcp_var.h>
+#include <netinet/tcpip.h>
+#include <netinet/udp.h>
+#include <netinet/udp_var.h>
+
+#include <machine/in_cksum.h>	/* XXX for in_cksum */
+
+MALLOC_DECLARE(M_IPFW);
+
+extern struct ip_fw_chain layer3_chain;
+
+static eventhandler_tag ifaddr_event_tag;
+
+extern ipfw_nat_t *ipfw_nat_ptr;
+extern ipfw_nat_cfg_t *ipfw_nat_cfg_ptr;
+extern ipfw_nat_cfg_t *ipfw_nat_del_ptr;
+extern ipfw_nat_cfg_t *ipfw_nat_get_cfg_ptr;
+extern ipfw_nat_cfg_t *ipfw_nat_get_log_ptr;
+
+static void 
+ifaddr_change(void *arg __unused, struct ifnet *ifp)
+{
+	struct cfg_nat *ptr;
+	struct ifaddr *ifa;
+
+	IPFW_WLOCK(&layer3_chain);			
+	/* Check every nat entry... */
+	LIST_FOREACH(ptr, &layer3_chain.nat, _next) {
+		/* ...using nic 'ifp->if_xname' as dynamic alias address. */
+		if (strncmp(ptr->if_name, ifp->if_xname, IF_NAMESIZE) == 0) {
+			mtx_lock(&ifp->if_addr_mtx);
+			TAILQ_FOREACH(ifa, &ifp->if_addrlist, ifa_list) {
+				if (ifa->ifa_addr == NULL)
+					continue;
+				if (ifa->ifa_addr->sa_family != AF_INET)
+					continue;
+				ptr->ip = ((struct sockaddr_in *) 
+				    (ifa->ifa_addr))->sin_addr;
+				LibAliasSetAddress(ptr->lib, ptr->ip);
+			}
+			mtx_unlock(&ifp->if_addr_mtx);
+		}
+	}
+	IPFW_WUNLOCK(&layer3_chain);	
+}
+
+static void
+flush_nat_ptrs(const int i)
+{
+	struct ip_fw *rule;
+
+	IPFW_WLOCK_ASSERT(&layer3_chain);
+	for (rule = layer3_chain.rules; rule; rule = rule->next) {
+		ipfw_insn_nat *cmd = (ipfw_insn_nat *)ACTION_PTR(rule);
+		if (cmd->o.opcode != O_NAT)
+			continue;
+		if (cmd->nat != NULL && cmd->nat->id == i)
+			cmd->nat = NULL;
+	}
+}
+
+#define HOOK_NAT(b, p) do {				\
+		IPFW_WLOCK_ASSERT(&layer3_chain);	\
+		LIST_INSERT_HEAD(b, p, _next);		\
+	} while (0)
+
+#define UNHOOK_NAT(p) do {				\
+		IPFW_WLOCK_ASSERT(&layer3_chain);	\
+		LIST_REMOVE(p, _next);			\
+	} while (0)
+
+#define HOOK_REDIR(b, p) do {			\
+		LIST_INSERT_HEAD(b, p, _next);	\
+	} while (0)
+
+#define HOOK_SPOOL(b, p) do {			\
+		LIST_INSERT_HEAD(b, p, _next);	\
+	} while (0)
+
+static void
+del_redir_spool_cfg(struct cfg_nat *n, struct redir_chain *head)
+{
+	struct cfg_redir *r, *tmp_r;
+	struct cfg_spool *s, *tmp_s;
+	int i, num;
+
+	LIST_FOREACH_SAFE(r, head, _next, tmp_r) {
+		num = 1; /* Number of alias_link to delete. */
+		switch (r->mode) {
+		case REDIR_PORT:
+			num = r->pport_cnt;
+			/* FALLTHROUGH */
+		case REDIR_ADDR:
+		case REDIR_PROTO:
+			/* Delete all libalias redirect entry. */
+			for (i = 0; i < num; i++)
+				LibAliasRedirectDelete(n->lib, r->alink[i]);
+			/* Del spool cfg if any. */
+			LIST_FOREACH_SAFE(s, &r->spool_chain, _next, tmp_s) {
+				LIST_REMOVE(s, _next);
+				free(s, M_IPFW);
+			}
+			free(r->alink, M_IPFW);
+			LIST_REMOVE(r, _next);
+			free(r, M_IPFW);
+			break;
+		default:
+			printf("unknown redirect mode: %u\n", r->mode);				
+			/* XXX - panic?!?!? */
+			break; 
+		}
+	}
+}
+
+static int
+add_redir_spool_cfg(char *buf, struct cfg_nat *ptr)
+{
+	struct cfg_redir *r, *ser_r;
+	struct cfg_spool *s, *ser_s;
+	int cnt, off, i;
+	char *panic_err;
+
+	for (cnt = 0, off = 0; cnt < ptr->redir_cnt; cnt++) {
+		ser_r = (struct cfg_redir *)&buf[off];
+		r = malloc(SOF_REDIR, M_IPFW, M_WAITOK | M_ZERO);
+		memcpy(r, ser_r, SOF_REDIR);
+		LIST_INIT(&r->spool_chain);
+		off += SOF_REDIR;
+		r->alink = malloc(sizeof(struct alias_link *) * r->pport_cnt,
+		    M_IPFW, M_WAITOK | M_ZERO);
+		switch (r->mode) {
+		case REDIR_ADDR:
+			r->alink[0] = LibAliasRedirectAddr(ptr->lib, r->laddr,
+			    r->paddr);
+			break;
+		case REDIR_PORT:
+			for (i = 0 ; i < r->pport_cnt; i++) {
+				/* If remotePort is all ports, set it to 0. */
+				u_short remotePortCopy = r->rport + i;
+				if (r->rport_cnt == 1 && r->rport == 0)
+					remotePortCopy = 0;
+				r->alink[i] = LibAliasRedirectPort(ptr->lib,
+				    r->laddr, htons(r->lport + i), r->raddr,
+				    htons(remotePortCopy), r->paddr, 
+				    htons(r->pport + i), r->proto);
+				if (r->alink[i] == NULL) {
+					r->alink[0] = NULL;
+					break;
+				}
+			}
+			break;
+		case REDIR_PROTO:
+			r->alink[0] = LibAliasRedirectProto(ptr->lib ,r->laddr,
+			    r->raddr, r->paddr, r->proto);
+			break;
+		default:
+			printf("unknown redirect mode: %u\n", r->mode);
+			break; 
+		}
+		if (r->alink[0] == NULL) {
+			panic_err = "LibAliasRedirect* returned NULL";
+			goto bad;
+		} else /* LSNAT handling. */
+			for (i = 0; i < r->spool_cnt; i++) {
+				ser_s = (struct cfg_spool *)&buf[off];
+				s = malloc(SOF_REDIR, M_IPFW, 
+				    M_WAITOK | M_ZERO);
+				memcpy(s, ser_s, SOF_SPOOL);
+				LibAliasAddServer(ptr->lib, r->alink[0], 
+				    s->addr, htons(s->port));
+				off += SOF_SPOOL;
+				/* Hook spool entry. */
+				HOOK_SPOOL(&r->spool_chain, s);
+			}
+		/* And finally hook this redir entry. */
+		HOOK_REDIR(&ptr->redir_chain, r);
+	}
+	return (1);
+bad:
+	/* something really bad happened: panic! */
+	panic("%s\n", panic_err);
+}
+
+static int
+ipfw_nat(struct ip_fw_args *args, struct cfg_nat *t, struct mbuf *m)
+{
+	struct mbuf *mcl;
+	struct ip *ip;
+	/* XXX - libalias duct tape */
+	int ldt, retval;
+	char *c;
+
+	ldt = 0;
+	retval = 0;
+	if ((mcl = m_megapullup(m, m->m_pkthdr.len)) ==
+	    NULL)
+		goto badnat;
+	ip = mtod(mcl, struct ip *);
+	if (args->eh == NULL) {
+		ip->ip_len = htons(ip->ip_len);
+		ip->ip_off = htons(ip->ip_off);
+	}
+
+	/* 
+	 * XXX - Libalias checksum offload 'duct tape':
+	 * 
+	 * locally generated packets have only
+	 * pseudo-header checksum calculated
+	 * and libalias will screw it[1], so
+	 * mark them for later fix.  Moreover
+	 * there are cases when libalias
+	 * modify tcp packet data[2], mark it
+	 * for later fix too.
+	 *
+	 * [1] libalias was never meant to run
+	 * in kernel, so it doesn't have any
+	 * knowledge about checksum
+	 * offloading, and it expects a packet
+	 * with a full internet
+	 * checksum. Unfortunately, packets
+	 * generated locally will have just the
+	 * pseudo header calculated, and when
+	 * libalias tries to adjust the
+	 * checksum it will actually screw it.
+	 *
+	 * [2] when libalias modify tcp's data
+	 * content, full TCP checksum has to
+	 * be recomputed: the problem is that
+	 * libalias doesn't have any idea
+	 * about checksum offloading To
+	 * workaround this, we do not do
+	 * checksumming in LibAlias, but only
+	 * mark the packets in th_x2 field. If
+	 * we receive a marked packet, we
+	 * calculate correct checksum for it
+	 * aware of offloading.  Why such a
+	 * terrible hack instead of
+	 * recalculating checksum for each
+	 * packet?  Because the previous
+	 * checksum was not checked!
+	 * Recalculating checksums for EVERY
+	 * packet will hide ALL transmission
+	 * errors. Yes, marked packets still
+	 * suffer from this problem. But,
+	 * sigh, natd(8) has this problem,
+	 * too.
+	 *
+	 * TODO: -make libalias mbuf aware (so
+	 * it can handle delayed checksum and tso)
+	 */
+
+	if (mcl->m_pkthdr.rcvif == NULL && 
+	    mcl->m_pkthdr.csum_flags & 
+	    CSUM_DELAY_DATA)
+		ldt = 1;
+
+	c = mtod(mcl, char *);
+	if (args->oif == NULL)
+		retval = LibAliasIn(t->lib, c, 
+				    MCLBYTES);
+	else
+		retval = LibAliasOut(t->lib, c, 
+				     MCLBYTES);
+	if (retval != PKT_ALIAS_OK) {
+		/* XXX - should i add some logging? */
+		m_free(mcl);
+	badnat:
+		args->m = NULL;
+		return (IP_FW_DENY);
+	}
+	mcl->m_pkthdr.len = mcl->m_len = 
+	    ntohs(ip->ip_len);
+
+	/* 
+	 * XXX - libalias checksum offload 
+	 * 'duct tape' (see above) 
+	 */
+
+	if ((ip->ip_off & htons(IP_OFFMASK)) == 0 && 
+	    ip->ip_p == IPPROTO_TCP) {
+		struct tcphdr 	*th; 
+
+		th = (struct tcphdr *)(ip + 1);
+		if (th->th_x2) 
+			ldt = 1;
+	}
+
+	if (ldt) {
+		struct tcphdr 	*th;
+		struct udphdr 	*uh;
+		u_short cksum;
+
+		ip->ip_len = ntohs(ip->ip_len);
+		cksum = in_pseudo(
+		    ip->ip_src.s_addr,
+		    ip->ip_dst.s_addr, 
+		    htons(ip->ip_p + ip->ip_len - (ip->ip_hl << 2))
+		);
+					
+		switch (ip->ip_p) {
+		case IPPROTO_TCP:
+			th = (struct tcphdr *)(ip + 1);
+			/* 
+			 * Maybe it was set in 
+			 * libalias... 
+			 */
+			th->th_x2 = 0;
+			th->th_sum = cksum;
+			mcl->m_pkthdr.csum_data = 
+			    offsetof(struct tcphdr, th_sum);
+			break;
+		case IPPROTO_UDP:
+			uh = (struct udphdr *)(ip + 1);
+			uh->uh_sum = cksum;
+			mcl->m_pkthdr.csum_data = 
+			    offsetof(struct udphdr, uh_sum);
+			break;						
+		}
+		/* 
+		 * No hw checksum offloading: do it 
+		 * by ourself. 
+		 */
+		if ((mcl->m_pkthdr.csum_flags & 
+		     CSUM_DELAY_DATA) == 0) {
+			in_delayed_cksum(mcl);
+			mcl->m_pkthdr.csum_flags &= 
+			    ~CSUM_DELAY_DATA;
+		}
+		ip->ip_len = htons(ip->ip_len);
+	}
+
+	if (args->eh == NULL) {
+		ip->ip_len = ntohs(ip->ip_len);
+		ip->ip_off = ntohs(ip->ip_off);
+	}
+
+	args->m = mcl;
+	return (IP_FW_NAT);
+}
+
+static int 
+ipfw_nat_cfg(struct sockopt *sopt)
+{
+	struct cfg_nat *ptr, *ser_n;
+	char *buf;
+
+	buf = malloc(NAT_BUF_LEN, M_IPFW, M_WAITOK | M_ZERO);
+	sooptcopyin(sopt, buf, NAT_BUF_LEN, 
+	    sizeof(struct cfg_nat));
+	ser_n = (struct cfg_nat *)buf;
+
+	/* 
+	 * Find/create nat rule.
+	 */
+	IPFW_WLOCK(&layer3_chain);
+	LOOKUP_NAT(layer3_chain, ser_n->id, ptr);
+	if (ptr == NULL) {
+		/* New rule: allocate and init new instance. */
+		ptr = malloc(sizeof(struct cfg_nat), 
+		    M_IPFW, M_NOWAIT | M_ZERO);
+		if (ptr == NULL) {
+			IPFW_WUNLOCK(&layer3_chain);				
+			free(buf, M_IPFW);
+			return (ENOSPC);
+		}
+		ptr->lib = LibAliasInit(NULL);
+		if (ptr->lib == NULL) {
+			IPFW_WUNLOCK(&layer3_chain);
+			free(ptr, M_IPFW);
+			free(buf, M_IPFW);
+			return (EINVAL);
+		}
+		LIST_INIT(&ptr->redir_chain);
+	} else {
+		/* Entry already present: temporarly unhook it. */
+		UNHOOK_NAT(ptr);
+		flush_nat_ptrs(ser_n->id);
+	}
+	IPFW_WUNLOCK(&layer3_chain);
+
+	/* 
+	 * Basic nat configuration.
+	 */
+	ptr->id = ser_n->id;
+	/* 
+	 * XXX - what if this rule doesn't nat any ip and just 
+	 * redirect? 
+	 * do we set aliasaddress to 0.0.0.0?
+	 */
+	ptr->ip = ser_n->ip;
+	ptr->redir_cnt = ser_n->redir_cnt;
+	ptr->mode = ser_n->mode;
+	LibAliasSetMode(ptr->lib, ser_n->mode, ser_n->mode);
+	LibAliasSetAddress(ptr->lib, ptr->ip);
+	memcpy(ptr->if_name, ser_n->if_name, IF_NAMESIZE);
+
+	/* 
+	 * Redir and LSNAT configuration.
+	 */
+	/* Delete old cfgs. */
+	del_redir_spool_cfg(ptr, &ptr->redir_chain);
+	/* Add new entries. */
+	add_redir_spool_cfg(&buf[(sizeof(struct cfg_nat))], ptr);
+	free(buf, M_IPFW);
+	IPFW_WLOCK(&layer3_chain);
+	HOOK_NAT(&layer3_chain.nat, ptr);
+	IPFW_WUNLOCK(&layer3_chain);
+	return (0);
+}
+
+static int
+ipfw_nat_del(struct sockopt *sopt)
+{
+	struct cfg_nat *ptr;
+	int i;
+		
+	sooptcopyin(sopt, &i, sizeof i, sizeof i);
+	IPFW_WLOCK(&layer3_chain);
+	LOOKUP_NAT(layer3_chain, i, ptr);
+	if (ptr == NULL) {
+		IPFW_WUNLOCK(&layer3_chain);
+		return (EINVAL);
+	}
+	UNHOOK_NAT(ptr);
+	flush_nat_ptrs(i);
+	IPFW_WUNLOCK(&layer3_chain);
+	del_redir_spool_cfg(ptr, &ptr->redir_chain);
+	LibAliasUninit(ptr->lib);
+	free(ptr, M_IPFW);
+	return (0);
+}
+
+static int
+ipfw_nat_get_cfg(struct sockopt *sopt)
+{	
+	uint8_t *data;
+	struct cfg_nat *n;
+	struct cfg_redir *r;
+	struct cfg_spool *s;
+	int nat_cnt, off;
+		
+	nat_cnt = 0;
+	off = sizeof(nat_cnt);
+
+	data = malloc(NAT_BUF_LEN, M_IPFW, M_WAITOK | M_ZERO);
+	IPFW_RLOCK(&layer3_chain);
+	/* Serialize all the data. */
+	LIST_FOREACH(n, &layer3_chain.nat, _next) {
+		nat_cnt++;
+		if (off + SOF_NAT < NAT_BUF_LEN) {
+			bcopy(n, &data[off], SOF_NAT);
+			off += SOF_NAT;
+			LIST_FOREACH(r, &n->redir_chain, _next) {
+				if (off + SOF_REDIR < NAT_BUF_LEN) {
+					bcopy(r, &data[off], 
+					    SOF_REDIR);
+					off += SOF_REDIR;
+					LIST_FOREACH(s, &r->spool_chain, 
+					    _next) {
+						if (off + SOF_SPOOL < 
+						    NAT_BUF_LEN) {
+							bcopy(s, &data[off],
+							    SOF_SPOOL);
+							off += SOF_SPOOL;
+						} else
+							goto nospace;
+					}
+				} else
+					goto nospace;
+			}
+		} else
+			goto nospace;
+	}
+	bcopy(&nat_cnt, data, sizeof(nat_cnt));
+	IPFW_RUNLOCK(&layer3_chain);
+	sooptcopyout(sopt, data, NAT_BUF_LEN);
+	free(data, M_IPFW);
+	return (0);
+nospace:
+	IPFW_RUNLOCK(&layer3_chain);
+	printf("serialized data buffer not big enough:"
+	    "please increase NAT_BUF_LEN\n");
+	free(data, M_IPFW);
+	return (ENOSPC);
+}
+
+static int
+ipfw_nat_get_log(struct sockopt *sopt)
+{
+	uint8_t *data;
+	struct cfg_nat *ptr;
+	int i, size, cnt, sof;
+
+	data = NULL;
+	sof = LIBALIAS_BUF_SIZE;
+	cnt = 0;
+
+	IPFW_RLOCK(&layer3_chain);
+	size = i = 0;
+	LIST_FOREACH(ptr, &layer3_chain.nat, _next) {
+		if (ptr->lib->logDesc == NULL) 
+			continue;
+		cnt++;
+		size = cnt * (sof + sizeof(int));
+		data = realloc(data, size, M_IPFW, M_NOWAIT | M_ZERO);
+		if (data == NULL) {
+			IPFW_RUNLOCK(&layer3_chain);
+			return (ENOSPC);
+		}
+		bcopy(&ptr->id, &data[i], sizeof(int));
+		i += sizeof(int);
+		bcopy(ptr->lib->logDesc, &data[i], sof);
+		i += sof;
+	}
+	IPFW_RUNLOCK(&layer3_chain);
+	sooptcopyout(sopt, data, size);
+	free(data, M_IPFW);
+	return(0);
+}
+
+static void
+ipfw_nat_init(void)
+{
+
+	IPFW_WLOCK(&layer3_chain);
+	/* init ipfw hooks */
+	ipfw_nat_ptr = ipfw_nat;
+	ipfw_nat_cfg_ptr = ipfw_nat_cfg;
+	ipfw_nat_del_ptr = ipfw_nat_del;
+	ipfw_nat_get_cfg_ptr = ipfw_nat_get_cfg;
+	ipfw_nat_get_log_ptr = ipfw_nat_get_log;
+	IPFW_WUNLOCK(&layer3_chain);
+	ifaddr_event_tag = EVENTHANDLER_REGISTER(ifaddr_event, ifaddr_change, 
+	    NULL, EVENTHANDLER_PRI_ANY);
+}
+
+static void
+ipfw_nat_destroy(void)
+{
+	struct cfg_nat *ptr, *ptr_temp;
+	
+	IPFW_WLOCK(&layer3_chain);
+	LIST_FOREACH_SAFE(ptr, &layer3_chain.nat, _next, ptr_temp) {
+		LIST_REMOVE(ptr, _next);
+		del_redir_spool_cfg(ptr, &ptr->redir_chain);
+		LibAliasUninit(ptr->lib);
+		free(ptr, M_IPFW);
+	}
+	EVENTHANDLER_DEREGISTER(ifaddr_event, ifaddr_event_tag);
+	/* deregister ipfw_nat */
+	ipfw_nat_ptr = NULL;
+	IPFW_WUNLOCK(&layer3_chain);
+}
+
+static int
+ipfw_nat_modevent(module_t mod, int type, void *unused)
+{
+	int err = 0;
+
+	switch (type) {
+	case MOD_LOAD:
+		ipfw_nat_init();
+		break;
+
+	case MOD_UNLOAD:
+		ipfw_nat_destroy();
+		break;
+
+	default:
+		return EOPNOTSUPP;
+		break;
+	}
+	return err;
+}
+
+static moduledata_t ipfw_nat_mod = {
+	"ipfw_nat",
+	ipfw_nat_modevent,
+	0
+};
+
+DECLARE_MODULE(ipfw_nat, ipfw_nat_mod, SI_SUB_PROTO_IFATTACHDOMAIN, SI_ORDER_ANY);
+MODULE_DEPEND(ipfw_nat, libalias, 1, 1, 1);
+MODULE_DEPEND(ipfw_nat, ipfw, 2, 2, 2);
+MODULE_VERSION(ipfw_nat, 1);