ip_nat_helper.c
/* ip_nat_helper.c - generic support functions for NAT helpers
*
* (C) 2000-2002 Harald Welte <laforge@netfilter.org>
* (C) 2003-2004 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.
*
* 14 Jan 2002 Harald Welte <laforge@gnumonks.org>:
* - add support for SACK adjustment
* 14 Mar 2002 Harald Welte <laforge@gnumonks.org>:
* - merge SACK support into newnat API
* 16 Aug 2002 Brian J. Murrell <netfilter@interlinx.bc.ca>:
* - make ip_nat_resize_packet more generic (TCP and UDP)
* - add ip_nat_mangle_udp_packet
*/
#include <linux/config.h>
#include <linux/module.h>
#include <linux/kmod.h>
#include <linux/types.h>
#include <linux/timer.h>
#include <linux/skbuff.h>
#include <linux/netfilter_ipv4.h>
#include <net/checksum.h>
#include <net/icmp.h>
#include <net/ip.h>
#include <net/tcp.h>
#include <net/udp.h>
#define ASSERT_READ_LOCK(x)
#define ASSERT_WRITE_LOCK(x)
#include <linux/netfilter_ipv4/ip_conntrack.h>
#include <linux/netfilter_ipv4/ip_conntrack_helper.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/listhelp.h>
#if 0
#define DEBUGP printk
#define DUMP_OFFSET(x) printk("offset_before=%d, offset_after=%d, correction_pos=%u\n", x->offset_before, x->offset_after, x->correction_pos);
#else
#define DEBUGP(format, args...)
#define DUMP_OFFSET(x)
#endif
static DEFINE_SPINLOCK(ip_nat_seqofs_lock);
/* Setup TCP sequence correction given this change at this sequence */
static inline void
adjust_tcp_sequence(u32 seq,
int sizediff,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo)
{
int dir;
struct ip_nat_seq *this_way, *other_way;
DEBUGP("ip_nat_resize_packet: old_size = %u, new_size = %u\n",
(*skb)->len, new_size);
dir = CTINFO2DIR(ctinfo);
this_way = &ct->nat.info.seq[dir];
other_way = &ct->nat.info.seq[!dir];
DEBUGP("ip_nat_resize_packet: Seq_offset before: ");
DUMP_OFFSET(this_way);
spin_lock_bh(&ip_nat_seqofs_lock);
/* SYN adjust. If it's uninitialized, or this is after last
* correction, record it: we don't handle more than one
* adjustment in the window, but do deal with common case of a
* retransmit */
if (this_way->offset_before == this_way->offset_after
|| before(this_way->correction_pos, seq)) {
this_way->correction_pos = seq;
this_way->offset_before = this_way->offset_after;
this_way->offset_after += sizediff;
}
spin_unlock_bh(&ip_nat_seqofs_lock);
DEBUGP("ip_nat_resize_packet: Seq_offset after: ");
DUMP_OFFSET(this_way);
}
/* 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 = (unsigned char *)skb->nh.iph + dataoff;
/* move post-replacement */
memmove(data + match_offset + rep_len,
data + match_offset + match_len,
skb->tail - (data + match_offset + match_len));
/* insert data from buffer */
memcpy(data + match_offset, rep_buffer, rep_len);
/* update skb info */
if (rep_len > match_len) {
DEBUGP("ip_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 {
DEBUGP("ip_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);
}
/* fix IP hdr checksum information */
skb->nh.iph->tot_len = htons(skb->len);
ip_send_check(skb->nh.iph);
}
/* Unusual, but possible case. */
static int enlarge_skb(struct sk_buff **pskb, unsigned int extra)
{
struct sk_buff *nskb;
if ((*pskb)->len + extra > 65535)
return 0;
nskb = skb_copy_expand(*pskb, skb_headroom(*pskb), extra, GFP_ATOMIC);
if (!nskb)
return 0;
/* Transfer socket to new skb. */
if ((*pskb)->sk)
skb_set_owner_w(nskb, (*pskb)->sk);
kfree_skb(*pskb);
*pskb = nskb;
return 1;
}
/* 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, ...
*
* */
int
ip_nat_mangle_tcp_packet(struct sk_buff **pskb,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo,
unsigned int match_offset,
unsigned int match_len,
const char *rep_buffer,
unsigned int rep_len)
{
struct iphdr *iph;
struct tcphdr *tcph;
int datalen;
if (!skb_ip_make_writable(pskb, (*pskb)->len))
return 0;
if (rep_len > match_len
&& rep_len - match_len > skb_tailroom(*pskb)
&& !enlarge_skb(pskb, rep_len - match_len))
return 0;
SKB_LINEAR_ASSERT(*pskb);
iph = (*pskb)->nh.iph;
tcph = (void *)iph + iph->ihl*4;
mangle_contents(*pskb, iph->ihl*4 + tcph->doff*4,
match_offset, match_len, rep_buffer, rep_len);
datalen = (*pskb)->len - iph->ihl*4;
tcph->check = 0;
tcph->check = tcp_v4_check(tcph, datalen, iph->saddr, iph->daddr,
csum_partial((char *)tcph, datalen, 0));
if (rep_len != match_len) {
set_bit(IPS_SEQ_ADJUST_BIT, &ct->status);
adjust_tcp_sequence(ntohl(tcph->seq),
(int)rep_len - (int)match_len,
ct, ctinfo);
/* Tell TCP window tracking about seq change */
ip_conntrack_tcp_update(*pskb, ct, CTINFO2DIR(ctinfo));
}
return 1;
}
/* 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 ip_nat_mangle_tcp_packet which
* should be fairly easy to do.
*/
int
ip_nat_mangle_udp_packet(struct sk_buff **pskb,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo,
unsigned int match_offset,
unsigned int match_len,
const char *rep_buffer,
unsigned int rep_len)
{
struct iphdr *iph;
struct udphdr *udph;
/* UDP helpers might accidentally mangle the wrong packet */
iph = (*pskb)->nh.iph;
if ((*pskb)->len < iph->ihl*4 + sizeof(*udph) +
match_offset + match_len)
return 0;
if (!skb_ip_make_writable(pskb, (*pskb)->len))
return 0;
if (rep_len > match_len
&& rep_len - match_len > skb_tailroom(*pskb)
&& !enlarge_skb(pskb, rep_len - match_len))
return 0;
iph = (*pskb)->nh.iph;
udph = (void *)iph + iph->ihl*4;
mangle_contents(*pskb, iph->ihl*4 + sizeof(*udph),
match_offset, match_len, rep_buffer, rep_len);
/* update the length of the UDP packet */
udph->len = htons((*pskb)->len - iph->ihl*4);
/* fix udp checksum if udp checksum was previously calculated */
if (udph->check) {
int datalen = (*pskb)->len - iph->ihl * 4;
udph->check = 0;
udph->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
datalen, IPPROTO_UDP,
csum_partial((char *)udph,
datalen, 0));
}
return 1;
}
/* Adjust one found SACK option including checksum correction */
static void
sack_adjust(struct sk_buff *skb,
struct tcphdr *tcph,
unsigned int sackoff,
unsigned int sackend,
struct ip_nat_seq *natseq)
{
while (sackoff < sackend) {
struct tcp_sack_block *sack;
u_int32_t new_start_seq, new_end_seq;
sack = (void *)skb->data + sackoff;
if (after(ntohl(sack->start_seq) - natseq->offset_before,
natseq->correction_pos))
new_start_seq = ntohl(sack->start_seq)
- natseq->offset_after;
else
new_start_seq = ntohl(sack->start_seq)
- natseq->offset_before;
new_start_seq = htonl(new_start_seq);
if (after(ntohl(sack->end_seq) - natseq->offset_before,
natseq->correction_pos))
new_end_seq = ntohl(sack->end_seq)
- natseq->offset_after;
else
new_end_seq = ntohl(sack->end_seq)
- natseq->offset_before;
new_end_seq = htonl(new_end_seq);
DEBUGP("sack_adjust: start_seq: %d->%d, end_seq: %d->%d\n",
ntohl(sack->start_seq), new_start_seq,
ntohl(sack->end_seq), new_end_seq);
tcph->check =
ip_nat_cheat_check(~sack->start_seq, new_start_seq,
ip_nat_cheat_check(~sack->end_seq,
new_end_seq,
tcph->check));
sack->start_seq = new_start_seq;
sack->end_seq = new_end_seq;
sackoff += sizeof(*sack);
}
}
/* TCP SACK sequence number adjustment */
static inline unsigned int
ip_nat_sack_adjust(struct sk_buff **pskb,
struct tcphdr *tcph,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo)
{
unsigned int dir, optoff, optend;
optoff = (*pskb)->nh.iph->ihl*4 + sizeof(struct tcphdr);
optend = (*pskb)->nh.iph->ihl*4 + tcph->doff*4;
if (!skb_ip_make_writable(pskb, optend))
return 0;
dir = CTINFO2DIR(ctinfo);
while (optoff < optend) {
/* Usually: option, length. */
unsigned char *op = (*pskb)->data + optoff;
switch (op[0]) {
case TCPOPT_EOL:
return 1;
case TCPOPT_NOP:
optoff++;
continue;
default:
/* no partial options */
if (optoff + 1 == optend
|| optoff + op[1] > optend
|| op[1] < 2)
return 0;
if (op[0] == TCPOPT_SACK
&& op[1] >= 2+TCPOLEN_SACK_PERBLOCK
&& ((op[1] - 2) % TCPOLEN_SACK_PERBLOCK) == 0)
sack_adjust(*pskb, tcph, optoff+2,
optoff+op[1],
&ct->nat.info.seq[!dir]);
optoff += op[1];
}
}
return 1;
}
/* TCP sequence number adjustment. Returns 1 on success, 0 on failure */
int
ip_nat_seq_adjust(struct sk_buff **pskb,
struct ip_conntrack *ct,
enum ip_conntrack_info ctinfo)
{
struct tcphdr *tcph;
int dir, newseq, newack;
struct ip_nat_seq *this_way, *other_way;
dir = CTINFO2DIR(ctinfo);
this_way = &ct->nat.info.seq[dir];
other_way = &ct->nat.info.seq[!dir];
if (!skb_ip_make_writable(pskb, (*pskb)->nh.iph->ihl*4+sizeof(*tcph)))
return 0;
tcph = (void *)(*pskb)->data + (*pskb)->nh.iph->ihl*4;
if (after(ntohl(tcph->seq), this_way->correction_pos))
newseq = ntohl(tcph->seq) + this_way->offset_after;
else
newseq = ntohl(tcph->seq) + this_way->offset_before;
newseq = htonl(newseq);
if (after(ntohl(tcph->ack_seq) - other_way->offset_before,
other_way->correction_pos))
newack = ntohl(tcph->ack_seq) - other_way->offset_after;
else
newack = ntohl(tcph->ack_seq) - other_way->offset_before;
newack = htonl(newack);
tcph->check = ip_nat_cheat_check(~tcph->seq, newseq,
ip_nat_cheat_check(~tcph->ack_seq,
newack,
tcph->check));
DEBUGP("Adjusting sequence number from %u->%u, ack from %u->%u\n",
ntohl(tcph->seq), ntohl(newseq), ntohl(tcph->ack_seq),
ntohl(newack));
tcph->seq = newseq;
tcph->ack_seq = newack;
if (!ip_nat_sack_adjust(pskb, tcph, ct, ctinfo))
return 0;
ip_conntrack_tcp_update(*pskb, ct, dir);
return 1;
}
/* 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 ip_nat_follow_master(struct ip_conntrack *ct,
struct ip_conntrack_expect *exp)
{
struct ip_nat_range range;
/* This must be a fresh one. */
BUG_ON(ct->status & IPS_NAT_DONE_MASK);
/* Change src to where master sends to */
range.flags = IP_NAT_RANGE_MAP_IPS;
range.min_ip = range.max_ip
= ct->master->tuplehash[!exp->dir].tuple.dst.ip;
/* hook doesn't matter, but it has to do source manip */
ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
/* For DST manip, map port here to where it's expected. */
range.flags = (IP_NAT_RANGE_MAP_IPS | IP_NAT_RANGE_PROTO_SPECIFIED);
range.min = range.max = exp->saved_proto;
range.min_ip = range.max_ip
= ct->master->tuplehash[!exp->dir].tuple.src.ip;
/* hook doesn't matter, but it has to do destination manip */
ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
}