net/ipv4/netfilter/ip_nat_core.c

/* NAT for netfilter; shared with compatibility layer. */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
 *
 * 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/types.h>
#include <linux/timer.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4.h>
#include <linux/vmalloc.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>  /* For tcp_prot in getorigdst */
#include <linux/icmp.h>
#include <linux/udp.h>
#include <linux/jhash.h>

#define ASSERT_READ_LOCK(x)
#define ASSERT_WRITE_LOCK(x)

#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/netfilter_ipv4/ip_conntrack_core.h>
#include <linux/netfilter_ipv4/ip_conntrack_protocol.h>
#include <linux/netfilter_ipv4/ip_nat.h>
#include <linux/netfilter_ipv4/ip_nat_protocol.h>
#include <linux/netfilter_ipv4/ip_nat_core.h>
#include <linux/netfilter_ipv4/ip_nat_helper.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.h>
#include <linux/netfilter_ipv4/listhelp.h>

#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif

DEFINE_RWLOCK(ip_nat_lock);

/* Calculated at init based on memory size */
static unsigned int ip_nat_htable_size;

static struct list_head *bysource;

#define MAX_IP_NAT_PROTO 256
static struct ip_nat_protocol *ip_nat_protos[MAX_IP_NAT_PROTO];

static inline struct ip_nat_protocol *
__ip_nat_proto_find(u_int8_t protonum)
{
	return ip_nat_protos[protonum];
}

struct ip_nat_protocol *
ip_nat_proto_find_get(u_int8_t protonum)
{
	struct ip_nat_protocol *p;

	/* we need to disable preemption to make sure 'p' doesn't get
	 * removed until we've grabbed the reference */
	preempt_disable();
	p = __ip_nat_proto_find(protonum);
	if (!try_module_get(p->me))
		p = &ip_nat_unknown_protocol;
	preempt_enable();

	return p;
}
EXPORT_SYMBOL_GPL(ip_nat_proto_find_get);

void
ip_nat_proto_put(struct ip_nat_protocol *p)
{
	module_put(p->me);
}
EXPORT_SYMBOL_GPL(ip_nat_proto_put);

/* We keep an extra hash for each conntrack, for fast searching. */
static inline unsigned int
hash_by_src(const struct ip_conntrack_tuple *tuple)
{
	/* Original src, to ensure we map it consistently if poss. */
	return jhash_3words(tuple->src.ip, tuple->src.u.all,
			    tuple->dst.protonum, 0) % ip_nat_htable_size;
}

/* Noone using conntrack by the time this called. */
static void ip_nat_cleanup_conntrack(struct ip_conntrack *conn)
{
	if (!(conn->status & IPS_NAT_DONE_MASK))
		return;

	write_lock_bh(&ip_nat_lock);
	list_del(&conn->nat.info.bysource);
	write_unlock_bh(&ip_nat_lock);
}

/* We do checksum mangling, so if they were wrong before they're still
 * wrong.  Also works for incomplete packets (eg. ICMP dest
 * unreachables.) */
u_int16_t
ip_nat_cheat_check(u_int32_t oldvalinv, u_int32_t newval, u_int16_t oldcheck)
{
	u_int32_t diffs[] = { oldvalinv, newval };
	return csum_fold(csum_partial((char *)diffs, sizeof(diffs),
				      oldcheck^0xFFFF));
}
EXPORT_SYMBOL(ip_nat_cheat_check);

/* Is this tuple already taken? (not by us) */
int
ip_nat_used_tuple(const struct ip_conntrack_tuple *tuple,
		  const struct ip_conntrack *ignored_conntrack)
{
	/* Conntrack tracking doesn't keep track of outgoing tuples; only
	   incoming ones.  NAT means they don't have a fixed mapping,
	   so we invert the tuple and look for the incoming reply.

	   We could keep a separate hash if this proves too slow. */
	struct ip_conntrack_tuple reply;

	invert_tuplepr(&reply, tuple);
	return ip_conntrack_tuple_taken(&reply, ignored_conntrack);
}
EXPORT_SYMBOL(ip_nat_used_tuple);

/* If we source map this tuple so reply looks like reply_tuple, will
 * that meet the constraints of range. */
static int
in_range(const struct ip_conntrack_tuple *tuple,
	 const struct ip_nat_range *range)
{
	struct ip_nat_protocol *proto = 
				__ip_nat_proto_find(tuple->dst.protonum);

	/* If we are supposed to map IPs, then we must be in the
	   range specified, otherwise let this drag us onto a new src IP. */
	if (range->flags & IP_NAT_RANGE_MAP_IPS) {
		if (ntohl(tuple->src.ip) < ntohl(range->min_ip)
		    || ntohl(tuple->src.ip) > ntohl(range->max_ip))
			return 0;
	}

	if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)
	    || proto->in_range(tuple, IP_NAT_MANIP_SRC,
			       &range->min, &range->max))
		return 1;

	return 0;
}

static inline int
same_src(const struct ip_conntrack *ct,
	 const struct ip_conntrack_tuple *tuple)
{
	return (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.protonum
		== tuple->dst.protonum
		&& ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip
		== tuple->src.ip
		&& ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u.all
		== tuple->src.u.all);
}

/* Only called for SRC manip */
static int
find_appropriate_src(const struct ip_conntrack_tuple *tuple,
		     struct ip_conntrack_tuple *result,
		     const struct ip_nat_range *range)
{
	unsigned int h = hash_by_src(tuple);
	struct ip_conntrack *ct;

	read_lock_bh(&ip_nat_lock);
	list_for_each_entry(ct, &bysource[h], nat.info.bysource) {
		if (same_src(ct, tuple)) {
			/* Copy source part from reply tuple. */
			invert_tuplepr(result,
				       &ct->tuplehash[IP_CT_DIR_REPLY].tuple);
			result->dst = tuple->dst;

			if (in_range(result, range)) {
				read_unlock_bh(&ip_nat_lock);
				return 1;
			}
		}
	}
	read_unlock_bh(&ip_nat_lock);
	return 0;
}

/* For [FUTURE] fragmentation handling, we want the least-used
   src-ip/dst-ip/proto triple.  Fairness doesn't come into it.  Thus
   if the range specifies 1.2.3.4 ports 10000-10005 and 1.2.3.5 ports
   1-65535, we don't do pro-rata allocation based on ports; we choose
   the ip with the lowest src-ip/dst-ip/proto usage.
*/
static void
find_best_ips_proto(struct ip_conntrack_tuple *tuple,
		    const struct ip_nat_range *range,
		    const struct ip_conntrack *conntrack,
		    enum ip_nat_manip_type maniptype)
{
	u_int32_t *var_ipp;
	/* Host order */
	u_int32_t minip, maxip, j;

	/* No IP mapping?  Do nothing. */
	if (!(range->flags & IP_NAT_RANGE_MAP_IPS))
		return;

	if (maniptype == IP_NAT_MANIP_SRC)
		var_ipp = &tuple->src.ip;
	else
		var_ipp = &tuple->dst.ip;

	/* Fast path: only one choice. */
	if (range->min_ip == range->max_ip) {
		*var_ipp = range->min_ip;
		return;
	}

	/* Hashing source and destination IPs gives a fairly even
	 * spread in practice (if there are a small number of IPs
	 * involved, there usually aren't that many connections
	 * anyway).  The consistency means that servers see the same
	 * client coming from the same IP (some Internet Banking sites
	 * like this), even across reboots. */
	minip = ntohl(range->min_ip);
	maxip = ntohl(range->max_ip);
	j = jhash_2words(tuple->src.ip, tuple->dst.ip, 0);
	*var_ipp = htonl(minip + j % (maxip - minip + 1));
}

/* Manipulate the tuple into the range given.  For NF_IP_POST_ROUTING,
 * we change the source to map into the range.  For NF_IP_PRE_ROUTING
 * and NF_IP_LOCAL_OUT, we change the destination to map into the
 * range.  It might not be possible to get a unique tuple, but we try.
 * At worst (or if we race), we will end up with a final duplicate in
 * __ip_conntrack_confirm and drop the packet. */
static void
get_unique_tuple(struct ip_conntrack_tuple *tuple,
		 const struct ip_conntrack_tuple *orig_tuple,
		 const struct ip_nat_range *range,
		 struct ip_conntrack *conntrack,
		 enum ip_nat_manip_type maniptype)
{
	struct ip_nat_protocol *proto;

	/* 1) If this srcip/proto/src-proto-part is currently mapped,
	   and that same mapping gives a unique tuple within the given
	   range, use that.

	   This is only required for source (ie. NAT/masq) mappings.
	   So far, we don't do local source mappings, so multiple
	   manips not an issue.  */
	if (maniptype == IP_NAT_MANIP_SRC) {
		if (find_appropriate_src(orig_tuple, tuple, range)) {
			DEBUGP("get_unique_tuple: Found current src map\n");
			if (!ip_nat_used_tuple(tuple, conntrack))
				return;
		}
	}

	/* 2) Select the least-used IP/proto combination in the given
	   range. */
	*tuple = *orig_tuple;
	find_best_ips_proto(tuple, range, conntrack, maniptype);

	/* 3) The per-protocol part of the manip is made to map into
	   the range to make a unique tuple. */

	proto = ip_nat_proto_find_get(orig_tuple->dst.protonum);

	/* Only bother mapping if it's not already in range and unique */
	if ((!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)
	     || proto->in_range(tuple, maniptype, &range->min, &range->max))
	    && !ip_nat_used_tuple(tuple, conntrack)) {
		ip_nat_proto_put(proto);
		return;
	}

	/* Last change: get protocol to try to obtain unique tuple. */
	proto->unique_tuple(tuple, range, maniptype, conntrack);

	ip_nat_proto_put(proto);
}

unsigned int
ip_nat_setup_info(struct ip_conntrack *conntrack,
		  const struct ip_nat_range *range,
		  unsigned int hooknum)
{
	struct ip_conntrack_tuple curr_tuple, new_tuple;
	struct ip_nat_info *info = &conntrack->nat.info;
	int have_to_hash = !(conntrack->status & IPS_NAT_DONE_MASK);
	enum ip_nat_manip_type maniptype = HOOK2MANIP(hooknum);

	IP_NF_ASSERT(hooknum == NF_IP_PRE_ROUTING
		     || hooknum == NF_IP_POST_ROUTING
		     || hooknum == NF_IP_LOCAL_IN
		     || hooknum == NF_IP_LOCAL_OUT);
	BUG_ON(ip_nat_initialized(conntrack, maniptype));

	/* What we've got will look like inverse of reply. Normally
	   this is what is in the conntrack, except for prior
	   manipulations (future optimization: if num_manips == 0,
	   orig_tp =
	   conntrack->tuplehash[IP_CT_DIR_ORIGINAL].tuple) */
	invert_tuplepr(&curr_tuple,
		       &conntrack->tuplehash[IP_CT_DIR_REPLY].tuple);

	get_unique_tuple(&new_tuple, &curr_tuple, range, conntrack, maniptype);

	if (!ip_ct_tuple_equal(&new_tuple, &curr_tuple)) {
		struct ip_conntrack_tuple reply;

		/* Alter conntrack table so will recognize replies. */
		invert_tuplepr(&reply, &new_tuple);
		ip_conntrack_alter_reply(conntrack, &reply);

		/* Non-atomic: we own this at the moment. */
		if (maniptype == IP_NAT_MANIP_SRC)
			conntrack->status |= IPS_SRC_NAT;
		else
			conntrack->status |= IPS_DST_NAT;
	}

	/* Place in source hash if this is the first time. */
	if (have_to_hash) {
		unsigned int srchash
			= hash_by_src(&conntrack->tuplehash[IP_CT_DIR_ORIGINAL]
				      .tuple);
		write_lock_bh(&ip_nat_lock);
		list_add(&info->bysource, &bysource[srchash]);
		write_unlock_bh(&ip_nat_lock);
	}

	/* It's done. */
	if (maniptype == IP_NAT_MANIP_DST)
		set_bit(IPS_DST_NAT_DONE_BIT, &conntrack->status);
	else
		set_bit(IPS_SRC_NAT_DONE_BIT, &conntrack->status);

	return NF_ACCEPT;
}
EXPORT_SYMBOL(ip_nat_setup_info);

/* Returns true if succeeded. */
static int
manip_pkt(u_int16_t proto,
	  struct sk_buff **pskb,
	  unsigned int iphdroff,
	  const struct ip_conntrack_tuple *target,
	  enum ip_nat_manip_type maniptype)
{
	struct iphdr *iph;
	struct ip_nat_protocol *p;

	if (!skb_make_writable(pskb, iphdroff + sizeof(*iph)))
		return 0;

	iph = (void *)(*pskb)->data + iphdroff;

	/* Manipulate protcol part. */
	p = ip_nat_proto_find_get(proto);
	if (!p->manip_pkt(pskb, iphdroff, target, maniptype)) {
		ip_nat_proto_put(p);
		return 0;
	}
	ip_nat_proto_put(p);

	iph = (void *)(*pskb)->data + iphdroff;

	if (maniptype == IP_NAT_MANIP_SRC) {
		iph->check = ip_nat_cheat_check(~iph->saddr, target->src.ip,
						iph->check);
		iph->saddr = target->src.ip;
	} else {
		iph->check = ip_nat_cheat_check(~iph->daddr, target->dst.ip,
						iph->check);
		iph->daddr = target->dst.ip;
	}
	return 1;
}

/* Do packet manipulations according to ip_nat_setup_info. */
unsigned int ip_nat_packet(struct ip_conntrack *ct,
			   enum ip_conntrack_info ctinfo,
			   unsigned int hooknum,
			   struct sk_buff **pskb)
{
	enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
	unsigned long statusbit;
	enum ip_nat_manip_type mtype = HOOK2MANIP(hooknum);

	if (mtype == IP_NAT_MANIP_SRC)
		statusbit = IPS_SRC_NAT;
	else
		statusbit = IPS_DST_NAT;

	/* Invert if this is reply dir. */
	if (dir == IP_CT_DIR_REPLY)
		statusbit ^= IPS_NAT_MASK;

	/* Non-atomic: these bits don't change. */
	if (ct->status & statusbit) {
		struct ip_conntrack_tuple target;

		/* We are aiming to look like inverse of other direction. */
		invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);

		if (!manip_pkt(target.dst.protonum, pskb, 0, &target, mtype))
			return NF_DROP;
	}
	return NF_ACCEPT;
}
EXPORT_SYMBOL_GPL(ip_nat_packet);

/* Dir is direction ICMP is coming from (opposite to packet it contains) */
int ip_nat_icmp_reply_translation(struct sk_buff **pskb,
				  struct ip_conntrack *ct,
				  enum ip_nat_manip_type manip,
				  enum ip_conntrack_dir dir)
{
	struct {
		struct icmphdr icmp;
		struct iphdr ip;
	} *inside;
	struct ip_conntrack_tuple inner, target;
	int hdrlen = (*pskb)->nh.iph->ihl * 4;
	unsigned long statusbit;

	if (!skb_make_writable(pskb, hdrlen + sizeof(*inside)))
		return 0;

	inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;

	/* We're actually going to mangle it beyond trivial checksum
	   adjustment, so make sure the current checksum is correct. */
	if ((*pskb)->ip_summed != CHECKSUM_UNNECESSARY) {
		hdrlen = (*pskb)->nh.iph->ihl * 4;
		if ((u16)csum_fold(skb_checksum(*pskb, hdrlen,
						(*pskb)->len - hdrlen, 0)))
			return 0;
	}

	/* Must be RELATED */
	IP_NF_ASSERT((*pskb)->nfctinfo == IP_CT_RELATED ||
		     (*pskb)->nfctinfo == IP_CT_RELATED+IP_CT_IS_REPLY);

	/* Redirects on non-null nats must be dropped, else they'll
           start talking to each other without our translation, and be
           confused... --RR */
	if (inside->icmp.type == ICMP_REDIRECT) {
		/* If NAT isn't finished, assume it and drop. */
		if ((ct->status & IPS_NAT_DONE_MASK) != IPS_NAT_DONE_MASK)
			return 0;

		if (ct->status & IPS_NAT_MASK)
			return 0;
	}

	DEBUGP("icmp_reply_translation: translating error %p manp %u dir %s\n",
	       *pskb, manip, dir == IP_CT_DIR_ORIGINAL ? "ORIG" : "REPLY");

	if (!ip_ct_get_tuple(&inside->ip, *pskb, (*pskb)->nh.iph->ihl*4 +
	                     sizeof(struct icmphdr) + inside->ip.ihl*4,
	                     &inner,
			     __ip_conntrack_proto_find(inside->ip.protocol)))
		return 0;

	/* Change inner back to look like incoming packet.  We do the
	   opposite manip on this hook to normal, because it might not
	   pass all hooks (locally-generated ICMP).  Consider incoming
	   packet: PREROUTING (DST manip), routing produces ICMP, goes
	   through POSTROUTING (which must correct the DST manip). */
	if (!manip_pkt(inside->ip.protocol, pskb,
		       (*pskb)->nh.iph->ihl*4
		       + sizeof(inside->icmp),
		       &ct->tuplehash[!dir].tuple,
		       !manip))
		return 0;

	/* Reloading "inside" here since manip_pkt inner. */
	inside = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
	inside->icmp.checksum = 0;
	inside->icmp.checksum = csum_fold(skb_checksum(*pskb, hdrlen,
						       (*pskb)->len - hdrlen,
						       0));

	/* Change outer to look the reply to an incoming packet
	 * (proto 0 means don't invert per-proto part). */
	if (manip == IP_NAT_MANIP_SRC)
		statusbit = IPS_SRC_NAT;
	else
		statusbit = IPS_DST_NAT;

	/* Invert if this is reply dir. */
	if (dir == IP_CT_DIR_REPLY)
		statusbit ^= IPS_NAT_MASK;

	if (ct->status & statusbit) {
		invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
		if (!manip_pkt(0, pskb, 0, &target, manip))
			return 0;
	}

	return 1;
}
EXPORT_SYMBOL_GPL(ip_nat_icmp_reply_translation);

/* Protocol registration. */
int ip_nat_protocol_register(struct ip_nat_protocol *proto)
{
	int ret = 0;

	write_lock_bh(&ip_nat_lock);
	if (ip_nat_protos[proto->protonum] != &ip_nat_unknown_protocol) {
		ret = -EBUSY;
		goto out;
	}
	ip_nat_protos[proto->protonum] = proto;
 out:
	write_unlock_bh(&ip_nat_lock);
	return ret;
}
EXPORT_SYMBOL(ip_nat_protocol_register);

/* Noone stores the protocol anywhere; simply delete it. */
void ip_nat_protocol_unregister(struct ip_nat_protocol *proto)
{
	write_lock_bh(&ip_nat_lock);
	ip_nat_protos[proto->protonum] = &ip_nat_unknown_protocol;
	write_unlock_bh(&ip_nat_lock);

	/* Someone could be still looking at the proto in a bh. */
	synchronize_net();
}
EXPORT_SYMBOL(ip_nat_protocol_unregister);

#if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
    defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
int
ip_nat_port_range_to_nfattr(struct sk_buff *skb, 
			    const struct ip_nat_range *range)
{
	NFA_PUT(skb, CTA_PROTONAT_PORT_MIN, sizeof(u_int16_t),
		&range->min.tcp.port);
	NFA_PUT(skb, CTA_PROTONAT_PORT_MAX, sizeof(u_int16_t),
		&range->max.tcp.port);

	return 0;

nfattr_failure:
	return -1;
}

int
ip_nat_port_nfattr_to_range(struct nfattr *tb[], struct ip_nat_range *range)
{
	int ret = 0;
	
	/* we have to return whether we actually parsed something or not */

	if (tb[CTA_PROTONAT_PORT_MIN-1]) {
		ret = 1;
		range->min.tcp.port = 
			*(u_int16_t *)NFA_DATA(tb[CTA_PROTONAT_PORT_MIN-1]);
	}
	
	if (!tb[CTA_PROTONAT_PORT_MAX-1]) {
		if (ret) 
			range->max.tcp.port = range->min.tcp.port;
	} else {
		ret = 1;
		range->max.tcp.port = 
			*(u_int16_t *)NFA_DATA(tb[CTA_PROTONAT_PORT_MAX-1]);
	}

	return ret;
}
EXPORT_SYMBOL_GPL(ip_nat_port_nfattr_to_range);
EXPORT_SYMBOL_GPL(ip_nat_port_range_to_nfattr);
#endif

static int __init ip_nat_init(void)
{
	size_t i;

	/* Leave them the same for the moment. */
	ip_nat_htable_size = ip_conntrack_htable_size;

	/* One vmalloc for both hash tables */
	bysource = vmalloc(sizeof(struct list_head) * ip_nat_htable_size);
	if (!bysource)
		return -ENOMEM;

	/* Sew in builtin protocols. */
	write_lock_bh(&ip_nat_lock);
	for (i = 0; i < MAX_IP_NAT_PROTO; i++)
		ip_nat_protos[i] = &ip_nat_unknown_protocol;
	ip_nat_protos[IPPROTO_TCP] = &ip_nat_protocol_tcp;
	ip_nat_protos[IPPROTO_UDP] = &ip_nat_protocol_udp;
	ip_nat_protos[IPPROTO_ICMP] = &ip_nat_protocol_icmp;
	write_unlock_bh(&ip_nat_lock);

	for (i = 0; i < ip_nat_htable_size; i++) {
		INIT_LIST_HEAD(&bysource[i]);
	}

	/* FIXME: Man, this is a hack.  <SIGH> */
	IP_NF_ASSERT(ip_conntrack_destroyed == NULL);
	ip_conntrack_destroyed = &ip_nat_cleanup_conntrack;

	/* Initialize fake conntrack so that NAT will skip it */
	ip_conntrack_untracked.status |= IPS_NAT_DONE_MASK;
	return 0;
}

/* Clear NAT section of all conntracks, in case we're loaded again. */
static int clean_nat(struct ip_conntrack *i, void *data)
{
	memset(&i->nat, 0, sizeof(i->nat));
	i->status &= ~(IPS_NAT_MASK | IPS_NAT_DONE_MASK | IPS_SEQ_ADJUST);
	return 0;
}

static void __exit ip_nat_cleanup(void)
{
	ip_ct_iterate_cleanup(&clean_nat, NULL);
	ip_conntrack_destroyed = NULL;
	vfree(bysource);
}

MODULE_LICENSE("GPL");

module_init(ip_nat_init);
module_exit(ip_nat_cleanup);