redonkable/alistair23-linux
redonkable/alistair23-linux
1
0
Fork 0
Code Releases Activity
alistair23-linux/net/netfilter/nf_nat_helper.c
Thierry Du Tre 2eb0f624b7 netfilter: add NAT support for shifted portmap ranges 
This is a patch proposal to support shifted ranges in portmaps.  (i.e. tcp/udp
incoming port 5000-5100 on WAN redirected to LAN 192.168.1.5:2000-2100)

Currently DNAT only works for single port or identical port ranges.  (i.e.
ports 5000-5100 on WAN interface redirected to a LAN host while original
destination port is not altered) When different port ranges are configured,
either 'random' mode should be used, or else all incoming connections are
mapped onto the first port in the redirect range. (in described example
WAN:5000-5100 will all be mapped to 192.168.1.5:2000)

This patch introduces a new mode indicated by flag NF_NAT_RANGE_PROTO_OFFSET
which uses a base port value to calculate an offset with the destination port
present in the incoming stream. That offset is then applied as index within the
redirect port range (index modulo rangewidth to handle range overflow).

In described example the base port would be 5000. An incoming stream with
destination port 5004 would result in an offset value 4 which means that the
NAT'ed stream will be using destination port 2004.

Other possibilities include deterministic mapping of larger or multiple ranges
to a smaller range : WAN:5000-5999 -> LAN:5000-5099 (maps WAN port 5*xx to port
51xx)

This patch does not change any current behavior. It just adds new NAT proto
range functionality which must be selected via the specific flag when intended
to use.

A patch for iptables (libipt_DNAT.c + libip6t_DNAT.c) will also be proposed
which makes this functionality immediately available.

Signed-off-by: Thierry Du Tre <thierry@dtsystems.be>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
2018-04-24 10:29:12 +02:00

213 lines
6.2 KiB
C
Raw Blame History

/* nf_nat_helper.c - generic support functions for NAT helpers
*
* (C) 2000-2002 Harald Welte <laforge@netfilter.org>
* (C) 2003-2006 Netfilter Core Team <coreteam@netfilter.org>
* (C) 2007-2012 Patrick McHardy <kaber@trash.net>
*
* 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/gfp.h>
#include <linux/types.h>
#include <linux/skbuff.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <net/tcp.h>
#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_ecache.h>
#include <net/netfilter/nf_conntrack_expect.h>
#include <net/netfilter/nf_conntrack_seqadj.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_l3proto.h>
#include <net/netfilter/nf_nat_l4proto.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_helper.h>
/* Frobs data inside this packet, which is linear. */
static void mangle_contents(struct sk_buff *skb,
unsigned int dataoff,
unsigned int match_offset,
unsigned int match_len,
const char *rep_buffer,
unsigned int rep_len)
{
unsigned char *data;
BUG_ON(skb_is_nonlinear(skb));
data = skb_network_header(skb) + dataoff;
/* move post-replacement */
memmove(data + match_offset + rep_len,
data + match_offset + match_len,
skb_tail_pointer(skb) - (skb_network_header(skb) + dataoff +
match_offset + match_len));
/* insert data from buffer */
memcpy(data + match_offset, rep_buffer, rep_len);
/* update skb info */
if (rep_len > match_len) {
pr_debug("nf_nat_mangle_packet: Extending packet by "
"%u from %u bytes\n", rep_len - match_len, skb->len);
skb_put(skb, rep_len - match_len);
} else {
pr_debug("nf_nat_mangle_packet: Shrinking packet from "
"%u from %u bytes\n", match_len - rep_len, skb->len);
__skb_trim(skb, skb->len + rep_len - match_len);
}
if (nf_ct_l3num((struct nf_conn *)skb_nfct(skb)) == NFPROTO_IPV4) {
/* fix IP hdr checksum information */
ip_hdr(skb)->tot_len = htons(skb->len);
ip_send_check(ip_hdr(skb));
} else
ipv6_hdr(skb)->payload_len =
htons(skb->len - sizeof(struct ipv6hdr));
}
/* Unusual, but possible case. */
static bool enlarge_skb(struct sk_buff *skb, unsigned int extra)
{
if (skb->len + extra > 65535)
return false;
if (pskb_expand_head(skb, 0, extra - skb_tailroom(skb), GFP_ATOMIC))
return false;
return true;
}
/* Generic function for mangling variable-length address changes inside
* NATed TCP connections (like the PORT XXX,XXX,XXX,XXX,XXX,XXX
* command in FTP).
*
* Takes care about all the nasty sequence number changes, checksumming,
* skb enlargement, ...
*
* */
bool __nf_nat_mangle_tcp_packet(struct sk_buff *skb,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int protoff,
unsigned int match_offset,
unsigned int match_len,
const char *rep_buffer,
unsigned int rep_len, bool adjust)
{
const struct nf_nat_l3proto *l3proto;
struct tcphdr *tcph;
int oldlen, datalen;
if (!skb_make_writable(skb, skb->len))
return false;
if (rep_len > match_len &&
rep_len - match_len > skb_tailroom(skb) &&
!enlarge_skb(skb, rep_len - match_len))
return false;
SKB_LINEAR_ASSERT(skb);
tcph = (void *)skb->data + protoff;
oldlen = skb->len - protoff;
mangle_contents(skb, protoff + tcph->doff*4,
match_offset, match_len, rep_buffer, rep_len);
datalen = skb->len - protoff;
l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
l3proto->csum_recalc(skb, IPPROTO_TCP, tcph, &tcph->check,
datalen, oldlen);
if (adjust && rep_len != match_len)
nf_ct_seqadj_set(ct, ctinfo, tcph->seq,
(int)rep_len - (int)match_len);
return true;
}
EXPORT_SYMBOL(__nf_nat_mangle_tcp_packet);
/* Generic function for mangling variable-length address changes inside
* NATed UDP connections (like the CONNECT DATA XXXXX MESG XXXXX INDEX XXXXX
* command in the Amanda protocol)
*
* Takes care about all the nasty sequence number changes, checksumming,
* skb enlargement, ...
*
* XXX - This function could be merged with nf_nat_mangle_tcp_packet which
* should be fairly easy to do.
*/
bool
nf_nat_mangle_udp_packet(struct sk_buff *skb,
struct nf_conn *ct,
enum ip_conntrack_info ctinfo,
unsigned int protoff,
unsigned int match_offset,
unsigned int match_len,
const char *rep_buffer,
unsigned int rep_len)
{
const struct nf_nat_l3proto *l3proto;
struct udphdr *udph;
int datalen, oldlen;
if (!skb_make_writable(skb, skb->len))
return false;
if (rep_len > match_len &&
rep_len - match_len > skb_tailroom(skb) &&
!enlarge_skb(skb, rep_len - match_len))
return false;
udph = (void *)skb->data + protoff;
oldlen = skb->len - protoff;
mangle_contents(skb, protoff + sizeof(*udph),
match_offset, match_len, rep_buffer, rep_len);
/* update the length of the UDP packet */
datalen = skb->len - protoff;
udph->len = htons(datalen);
/* fix udp checksum if udp checksum was previously calculated */
if (!udph->check && skb->ip_summed != CHECKSUM_PARTIAL)
return true;
l3proto = __nf_nat_l3proto_find(nf_ct_l3num(ct));
l3proto->csum_recalc(skb, IPPROTO_UDP, udph, &udph->check,
datalen, oldlen);
return true;
}
EXPORT_SYMBOL(nf_nat_mangle_udp_packet);
/* Setup NAT on this expected conntrack so it follows master. */
/* If we fail to get a free NAT slot, we'll get dropped on confirm */
void nf_nat_follow_master(struct nf_conn *ct,
struct nf_conntrack_expect *exp)
{
struct nf_nat_range2 range;
/* This must be a fresh one. */
BUG_ON(ct->status & IPS_NAT_DONE_MASK);
/* Change src to where master sends to */
range.flags = NF_NAT_RANGE_MAP_IPS;
range.min_addr = range.max_addr
= ct->master->tuplehash[!exp->dir].tuple.dst.u3;
nf_nat_setup_info(ct, &range, NF_NAT_MANIP_SRC);
/* For DST manip, map port here to where it's expected. */
range.flags = (NF_NAT_RANGE_MAP_IPS | NF_NAT_RANGE_PROTO_SPECIFIED);
range.min_proto = range.max_proto = exp->saved_proto;
range.min_addr = range.max_addr
= ct->master->tuplehash[!exp->dir].tuple.src.u3;
nf_nat_setup_info(ct, &range, NF_NAT_MANIP_DST);
}
EXPORT_SYMBOL(nf_nat_follow_master);
View git blame Copy permalink