nf_nat_core.c
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/* NAT for netfilter; shared with compatibility layer. */
/* (C) 1999-2001 Paul `Rusty' Russell
* (C) 2002-2006 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/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>
#include <linux/netfilter_ipv4.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_core.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_protocol.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_helper.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_l3proto.h>
#include <net/netfilter/nf_conntrack_l4proto.h>
#if 0
#define DEBUGP printk
#else
#define DEBUGP(format, args...)
#endif
static DEFINE_RWLOCK(nf_nat_lock);
static struct nf_conntrack_l3proto *l3proto = NULL;
/* Calculated at init based on memory size */
static unsigned int nf_nat_htable_size;
static struct list_head *bysource;
#define MAX_IP_NAT_PROTO 256
static struct nf_nat_protocol *nf_nat_protos[MAX_IP_NAT_PROTO];
static inline struct nf_nat_protocol *
__nf_nat_proto_find(u_int8_t protonum)
{
return rcu_dereference(nf_nat_protos[protonum]);
}
struct nf_nat_protocol *
nf_nat_proto_find_get(u_int8_t protonum)
{
struct nf_nat_protocol *p;
rcu_read_lock();
p = __nf_nat_proto_find(protonum);
if (!try_module_get(p->me))
p = &nf_nat_unknown_protocol;
rcu_read_unlock();
return p;
}
EXPORT_SYMBOL_GPL(nf_nat_proto_find_get);
void
nf_nat_proto_put(struct nf_nat_protocol *p)
{
module_put(p->me);
}
EXPORT_SYMBOL_GPL(nf_nat_proto_put);
/* We keep an extra hash for each conntrack, for fast searching. */
static inline unsigned int
hash_by_src(const struct nf_conntrack_tuple *tuple)
{
/* Original src, to ensure we map it consistently if poss. */
return jhash_3words((__force u32)tuple->src.u3.ip, tuple->src.u.all,
tuple->dst.protonum, 0) % nf_nat_htable_size;
}
/* Noone using conntrack by the time this called. */
static void nf_nat_cleanup_conntrack(struct nf_conn *conn)
{
struct nf_conn_nat *nat;
if (!(conn->status & IPS_NAT_DONE_MASK))
return;
nat = nfct_nat(conn);
write_lock_bh(&nf_nat_lock);
list_del(&nat->info.bysource);
nat->info.ct = NULL;
write_unlock_bh(&nf_nat_lock);
}
/* Is this tuple already taken? (not by us) */
int
nf_nat_used_tuple(const struct nf_conntrack_tuple *tuple,
const struct nf_conn *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 nf_conntrack_tuple reply;
nf_ct_invert_tuplepr(&reply, tuple);
return nf_conntrack_tuple_taken(&reply, ignored_conntrack);
}
EXPORT_SYMBOL(nf_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 nf_conntrack_tuple *tuple,
const struct nf_nat_range *range)
{
struct nf_nat_protocol *proto;
int ret = 0;
/* 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.u3.ip) < ntohl(range->min_ip) ||
ntohl(tuple->src.u3.ip) > ntohl(range->max_ip))
return 0;
}
rcu_read_lock();
proto = __nf_nat_proto_find(tuple->dst.protonum);
if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED) ||
proto->in_range(tuple, IP_NAT_MANIP_SRC,
&range->min, &range->max))
ret = 1;
rcu_read_unlock();
return ret;
}
static inline int
same_src(const struct nf_conn *ct,
const struct nf_conntrack_tuple *tuple)
{
const struct nf_conntrack_tuple *t;
t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
return (t->dst.protonum == tuple->dst.protonum &&
t->src.u3.ip == tuple->src.u3.ip &&
t->src.u.all == tuple->src.u.all);
}
/* Only called for SRC manip */
static int
find_appropriate_src(const struct nf_conntrack_tuple *tuple,
struct nf_conntrack_tuple *result,
const struct nf_nat_range *range)
{
unsigned int h = hash_by_src(tuple);
struct nf_conn_nat *nat;
struct nf_conn *ct;
read_lock_bh(&nf_nat_lock);
list_for_each_entry(nat, &bysource[h], info.bysource) {
ct = nat->info.ct;
if (same_src(ct, tuple)) {
/* Copy source part from reply tuple. */
nf_ct_invert_tuplepr(result,
&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
result->dst = tuple->dst;
if (in_range(result, range)) {
read_unlock_bh(&nf_nat_lock);
return 1;
}
}
}
read_unlock_bh(&nf_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 nf_conntrack_tuple *tuple,
const struct nf_nat_range *range,
const struct nf_conn *ct,
enum nf_nat_manip_type maniptype)
{
__be32 *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.u3.ip;
else
var_ipp = &tuple->dst.u3.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((__force u32)tuple->src.u3.ip,
(__force u32)tuple->dst.u3.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 nf_conntrack_tuple *tuple,
const struct nf_conntrack_tuple *orig_tuple,
const struct nf_nat_range *range,
struct nf_conn *ct,
enum nf_nat_manip_type maniptype)
{
struct nf_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 (!(range->flags & IP_NAT_RANGE_PROTO_RANDOM))
if (!nf_nat_used_tuple(tuple, ct))
return;
}
}
/* 2) Select the least-used IP/proto combination in the given
range. */
*tuple = *orig_tuple;
find_best_ips_proto(tuple, range, ct, maniptype);
/* 3) The per-protocol part of the manip is made to map into
the range to make a unique tuple. */
rcu_read_lock();
proto = __nf_nat_proto_find(orig_tuple->dst.protonum);
/* Change protocol info to have some randomization */
if (range->flags & IP_NAT_RANGE_PROTO_RANDOM) {
proto->unique_tuple(tuple, range, maniptype, ct);
goto out;
}
/* 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)) &&
!nf_nat_used_tuple(tuple, ct))
goto out;
/* Last change: get protocol to try to obtain unique tuple. */
proto->unique_tuple(tuple, range, maniptype, ct);
out:
rcu_read_unlock();
}
unsigned int
nf_nat_setup_info(struct nf_conn *ct,
const struct nf_nat_range *range,
unsigned int hooknum)
{
struct nf_conntrack_tuple curr_tuple, new_tuple;
struct nf_conn_nat *nat = nfct_nat(ct);
struct nf_nat_info *info = &nat->info;
int have_to_hash = !(ct->status & IPS_NAT_DONE_MASK);
enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
NF_CT_ASSERT(hooknum == NF_IP_PRE_ROUTING ||
hooknum == NF_IP_POST_ROUTING ||
hooknum == NF_IP_LOCAL_IN ||
hooknum == NF_IP_LOCAL_OUT);
BUG_ON(nf_nat_initialized(ct, 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) */
nf_ct_invert_tuplepr(&curr_tuple,
&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
get_unique_tuple(&new_tuple, &curr_tuple, range, ct, maniptype);
if (!nf_ct_tuple_equal(&new_tuple, &curr_tuple)) {
struct nf_conntrack_tuple reply;
/* Alter conntrack table so will recognize replies. */
nf_ct_invert_tuplepr(&reply, &new_tuple);
nf_conntrack_alter_reply(ct, &reply);
/* Non-atomic: we own this at the moment. */
if (maniptype == IP_NAT_MANIP_SRC)
ct->status |= IPS_SRC_NAT;
else
ct->status |= IPS_DST_NAT;
}
/* Place in source hash if this is the first time. */
if (have_to_hash) {
unsigned int srchash;
srchash = hash_by_src(&ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple);
write_lock_bh(&nf_nat_lock);
info->ct = ct;
list_add(&info->bysource, &bysource[srchash]);
write_unlock_bh(&nf_nat_lock);
}
/* It's done. */
if (maniptype == IP_NAT_MANIP_DST)
set_bit(IPS_DST_NAT_DONE_BIT, &ct->status);
else
set_bit(IPS_SRC_NAT_DONE_BIT, &ct->status);
return NF_ACCEPT;
}
EXPORT_SYMBOL(nf_nat_setup_info);
/* Returns true if succeeded. */
static int
manip_pkt(u_int16_t proto,
struct sk_buff **pskb,
unsigned int iphdroff,
const struct nf_conntrack_tuple *target,
enum nf_nat_manip_type maniptype)
{
struct iphdr *iph;
struct nf_nat_protocol *p;
if (!skb_make_writable(pskb, iphdroff + sizeof(*iph)))
return 0;
iph = (void *)(*pskb)->data + iphdroff;
/* Manipulate protcol part. */
/* rcu_read_lock()ed by nf_hook_slow */
p = __nf_nat_proto_find(proto);
if (!p->manip_pkt(pskb, iphdroff, target, maniptype))
return 0;
iph = (void *)(*pskb)->data + iphdroff;
if (maniptype == IP_NAT_MANIP_SRC) {
nf_csum_replace4(&iph->check, iph->saddr, target->src.u3.ip);
iph->saddr = target->src.u3.ip;
} else {
nf_csum_replace4(&iph->check, iph->daddr, target->dst.u3.ip);
iph->daddr = target->dst.u3.ip;
}
return 1;
}
/* Do packet manipulations according to nf_nat_setup_info. */
unsigned int nf_nat_packet(struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int hooknum,
struct sk_buff **pskb)
{
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
unsigned long statusbit;
enum nf_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 nf_conntrack_tuple target;
/* We are aiming to look like inverse of other direction. */
nf_ct_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(nf_nat_packet);
/* Dir is direction ICMP is coming from (opposite to packet it contains) */
int nf_nat_icmp_reply_translation(struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int hooknum,
struct sk_buff **pskb)
{
struct {
struct icmphdr icmp;
struct iphdr ip;
} *inside;
struct nf_conntrack_l4proto *l4proto;
struct nf_conntrack_tuple inner, target;
int hdrlen = ip_hdrlen(*pskb);
enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
unsigned long statusbit;
enum nf_nat_manip_type manip = HOOK2MANIP(hooknum);
if (!skb_make_writable(pskb, hdrlen + sizeof(*inside)))
return 0;
inside = (void *)(*pskb)->data + ip_hdrlen(*pskb);
/* We're actually going to mangle it beyond trivial checksum
adjustment, so make sure the current checksum is correct. */
if (nf_ip_checksum(*pskb, hooknum, hdrlen, 0))
return 0;
/* Must be RELATED */
NF_CT_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");
/* rcu_read_lock()ed by nf_hook_slow */
l4proto = __nf_ct_l4proto_find(PF_INET, inside->ip.protocol);
if (!nf_ct_get_tuple(*pskb,
ip_hdrlen(*pskb) + sizeof(struct icmphdr),
(ip_hdrlen(*pskb) +
sizeof(struct icmphdr) + inside->ip.ihl * 4),
(u_int16_t)AF_INET,
inside->ip.protocol,
&inner, l3proto, l4proto))
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,
ip_hdrlen(*pskb) + sizeof(inside->icmp),
&ct->tuplehash[!dir].tuple,
!manip))
return 0;
if ((*pskb)->ip_summed != CHECKSUM_PARTIAL) {
/* Reloading "inside" here since manip_pkt inner. */
inside = (void *)(*pskb)->data + ip_hdrlen(*pskb);
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) {
nf_ct_invert_tuplepr(&target, &ct->tuplehash[!dir].tuple);
if (!manip_pkt(0, pskb, 0, &target, manip))
return 0;
}
return 1;
}
EXPORT_SYMBOL_GPL(nf_nat_icmp_reply_translation);
/* Protocol registration. */
int nf_nat_protocol_register(struct nf_nat_protocol *proto)
{
int ret = 0;
write_lock_bh(&nf_nat_lock);
if (nf_nat_protos[proto->protonum] != &nf_nat_unknown_protocol) {
ret = -EBUSY;
goto out;
}
rcu_assign_pointer(nf_nat_protos[proto->protonum], proto);
out:
write_unlock_bh(&nf_nat_lock);
return ret;
}
EXPORT_SYMBOL(nf_nat_protocol_register);
/* Noone stores the protocol anywhere; simply delete it. */
void nf_nat_protocol_unregister(struct nf_nat_protocol *proto)
{
write_lock_bh(&nf_nat_lock);
rcu_assign_pointer(nf_nat_protos[proto->protonum],
&nf_nat_unknown_protocol);
write_unlock_bh(&nf_nat_lock);
synchronize_rcu();
}
EXPORT_SYMBOL(nf_nat_protocol_unregister);
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
int
nf_nat_port_range_to_nfattr(struct sk_buff *skb,
const struct nf_nat_range *range)
{
NFA_PUT(skb, CTA_PROTONAT_PORT_MIN, sizeof(__be16),
&range->min.tcp.port);
NFA_PUT(skb, CTA_PROTONAT_PORT_MAX, sizeof(__be16),
&range->max.tcp.port);
return 0;
nfattr_failure:
return -1;
}
EXPORT_SYMBOL_GPL(nf_nat_port_nfattr_to_range);
int
nf_nat_port_nfattr_to_range(struct nfattr *tb[], struct nf_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 =
*(__be16 *)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 =
*(__be16 *)NFA_DATA(tb[CTA_PROTONAT_PORT_MAX-1]);
}
return ret;
}
EXPORT_SYMBOL_GPL(nf_nat_port_range_to_nfattr);
#endif
static int __init nf_nat_init(void)
{
size_t i;
/* Leave them the same for the moment. */
nf_nat_htable_size = nf_conntrack_htable_size;
/* One vmalloc for both hash tables */
bysource = vmalloc(sizeof(struct list_head) * nf_nat_htable_size);
if (!bysource)
return -ENOMEM;
/* Sew in builtin protocols. */
write_lock_bh(&nf_nat_lock);
for (i = 0; i < MAX_IP_NAT_PROTO; i++)
rcu_assign_pointer(nf_nat_protos[i], &nf_nat_unknown_protocol);
rcu_assign_pointer(nf_nat_protos[IPPROTO_TCP], &nf_nat_protocol_tcp);
rcu_assign_pointer(nf_nat_protos[IPPROTO_UDP], &nf_nat_protocol_udp);
rcu_assign_pointer(nf_nat_protos[IPPROTO_ICMP], &nf_nat_protocol_icmp);
write_unlock_bh(&nf_nat_lock);
for (i = 0; i < nf_nat_htable_size; i++) {
INIT_LIST_HEAD(&bysource[i]);
}
/* FIXME: Man, this is a hack. <SIGH> */
NF_CT_ASSERT(rcu_dereference(nf_conntrack_destroyed) == NULL);
rcu_assign_pointer(nf_conntrack_destroyed, nf_nat_cleanup_conntrack);
/* Initialize fake conntrack so that NAT will skip it */
nf_conntrack_untracked.status |= IPS_NAT_DONE_MASK;
l3proto = nf_ct_l3proto_find_get((u_int16_t)AF_INET);
return 0;
}
/* Clear NAT section of all conntracks, in case we're loaded again. */
static int clean_nat(struct nf_conn *i, void *data)
{
struct nf_conn_nat *nat = nfct_nat(i);
if (!nat)
return 0;
memset(nat, 0, sizeof(nat));
i->status &= ~(IPS_NAT_MASK | IPS_NAT_DONE_MASK | IPS_SEQ_ADJUST);
return 0;
}
static void __exit nf_nat_cleanup(void)
{
nf_ct_iterate_cleanup(&clean_nat, NULL);
rcu_assign_pointer(nf_conntrack_destroyed, NULL);
synchronize_rcu();
vfree(bysource);
nf_ct_l3proto_put(l3proto);
}
MODULE_LICENSE("GPL");
module_init(nf_nat_init);
module_exit(nf_nat_cleanup);