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#include <linux/config.h>
#include <linux/netfilter.h>
#include <linux/ip.h>
#include <linux/udp.h>
#include <linux/tcp.h>
#include <net/checksum.h>
#include <linux/timer.h>
#include <linux/netdevice.h>
#include <linux/if.h>
#include <linux/in.h>
#include <linux/netfilter_ipv4/lockhelp.h>
/* Very simple timeout pushed back by each packet */
#define REDIR_TIMEOUT (240*HZ)
static DECLARE_LOCK(redir_lock);
#define ASSERT_READ_LOCK(x) MUST_BE_LOCKED(&redir_lock)
#define ASSERT_WRITE_LOCK(x) MUST_BE_LOCKED(&redir_lock)
#include <linux/netfilter_ipv4/listhelp.h>
#define DEBUGP(format, args...)
#ifdef CONFIG_NETFILTER_DEBUG
#define IP_NF_ASSERT(x) \
do { \
if (!(x)) \
/* Wooah! I'm tripping my conntrack in a frenzy of \
netplay... */ \
printk("ASSERT: %s:%i(%s)\n", \
__FILE__, __LINE__, __FUNCTION__); \
} while(0)
#else
#define IP_NF_ASSERT(x)
#endif
static u_int16_t
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));
}
struct redir_core {
u_int32_t orig_srcip, orig_dstip;
u_int16_t orig_sport, orig_dport;
u_int32_t new_dstip;
u_int16_t new_dport;
};
struct redir
{
struct list_head list;
struct redir_core core;
struct timer_list destroyme;
};
static LIST_HEAD(redirs);
static int
redir_cmp(const struct redir *i,
u_int32_t orig_srcip, u_int32_t orig_dstip,
u_int16_t orig_sport, u_int16_t orig_dport)
{
return (i->core.orig_srcip == orig_srcip
&& i->core.orig_dstip == orig_dstip
&& i->core.orig_sport == orig_sport
&& i->core.orig_dport == orig_dport);
}
/* Search for an existing redirection of the TCP packet. */
static struct redir *
find_redir(u_int32_t orig_srcip, u_int32_t orig_dstip,
u_int16_t orig_sport, u_int16_t orig_dport)
{
return LIST_FIND(&redirs, redir_cmp, struct redir *,
orig_srcip, orig_dstip, orig_sport, orig_dport);
}
static void do_tcp_redir(struct sk_buff *skb, struct redir *redir)
{
struct iphdr *iph = skb->nh.iph;
struct tcphdr *tcph = (struct tcphdr *)((u_int32_t *)iph
+ iph->ihl);
tcph->check = cheat_check(~redir->core.orig_dstip,
redir->core.new_dstip,
cheat_check(redir->core.orig_dport ^ 0xFFFF,
redir->core.new_dport,
tcph->check));
iph->check = cheat_check(~redir->core.orig_dstip,
redir->core.new_dstip, iph->check);
tcph->dest = redir->core.new_dport;
iph->daddr = redir->core.new_dstip;
skb->nfcache |= NFC_ALTERED;
}
static int
unredir_cmp(const struct redir *i,
u_int32_t new_dstip, u_int32_t orig_srcip,
u_int16_t new_dport, u_int16_t orig_sport)
{
return (i->core.orig_srcip == orig_srcip
&& i->core.new_dstip == new_dstip
&& i->core.orig_sport == orig_sport
&& i->core.new_dport == new_dport);
}
/* Match reply packet against redir */
static struct redir *
find_unredir(u_int32_t new_dstip, u_int32_t orig_srcip,
u_int16_t new_dport, u_int16_t orig_sport)
{
return LIST_FIND(&redirs, unredir_cmp, struct redir *,
new_dstip, orig_srcip, new_dport, orig_sport);
}
/* `unredir' a reply packet. */
static void do_tcp_unredir(struct sk_buff *skb, struct redir *redir)
{
struct iphdr *iph = skb->nh.iph;
struct tcphdr *tcph = (struct tcphdr *)((u_int32_t *)iph
+ iph->ihl);
tcph->check = cheat_check(~redir->core.new_dstip,
redir->core.orig_dstip,
cheat_check(redir->core.new_dport ^ 0xFFFF,
redir->core.orig_dport,
tcph->check));
iph->check = cheat_check(~redir->core.new_dstip,
redir->core.orig_dstip,
iph->check);
tcph->source = redir->core.orig_dport;
iph->saddr = redir->core.orig_dstip;
skb->nfcache |= NFC_ALTERED;
}
static void destroyme(unsigned long me)
{
LOCK_BH(&redir_lock);
LIST_DELETE(&redirs, (struct redir *)me);
UNLOCK_BH(&redir_lock);
kfree((struct redir *)me);
}
/* REDIRECT a packet. */
unsigned int
do_redirect(struct sk_buff *skb,
const struct net_device *dev,
u_int16_t redirpt)
{
struct iphdr *iph = skb->nh.iph;
u_int32_t newdst;
/* Figure out address: not loopback. */
if (!dev)
return NF_DROP;
/* Grab first address on interface. */
newdst = ((struct in_device *)dev->ip_ptr)->ifa_list->ifa_local;
switch (iph->protocol) {
case IPPROTO_UDP: {
/* Simple mangle. */
struct udphdr *udph = (struct udphdr *)((u_int32_t *)iph
+ iph->ihl);
/* Must have whole header */
if (skb->len < iph->ihl*4 + sizeof(*udph))
return NF_DROP;
if (udph->check) /* 0 is a special case meaning no checksum */
udph->check = cheat_check(~iph->daddr, newdst,
cheat_check(udph->dest ^ 0xFFFF,
redirpt,
udph->check));
iph->check = cheat_check(~iph->daddr, newdst, iph->check);
udph->dest = redirpt;
iph->daddr = newdst;
skb->nfcache |= NFC_ALTERED;
return NF_ACCEPT;
}
case IPPROTO_TCP: {
/* Mangle, maybe record. */
struct tcphdr *tcph = (struct tcphdr *)((u_int32_t *)iph
+ iph->ihl);
struct redir *redir;
int ret;
/* Must have whole header */
if (skb->len < iph->ihl*4 + sizeof(*tcph))
return NF_DROP;
DEBUGP("Doing tcp redirect. %08X:%u %08X:%u -> %08X:%u\n",
iph->saddr, tcph->source, iph->daddr, tcph->dest,
newdst, redirpt);
LOCK_BH(&redir_lock);
redir = find_redir(iph->saddr, iph->daddr,
tcph->source, tcph->dest);
if (!redir) {
redir = kmalloc(sizeof(struct redir), GFP_ATOMIC);
if (!redir) {
ret = NF_DROP;
goto out;
}
list_prepend(&redirs, redir);
init_timer(&redir->destroyme);
redir->destroyme.function = destroyme;
redir->destroyme.data = (unsigned long)redir;
redir->destroyme.expires = jiffies + REDIR_TIMEOUT;
add_timer(&redir->destroyme);
}
/* In case mangling has changed, rewrite this part. */
redir->core = ((struct redir_core)
{ iph->saddr, iph->daddr,
tcph->source, tcph->dest,
newdst, redirpt });
do_tcp_redir(skb, redir);
ret = NF_ACCEPT;
out:
UNLOCK_BH(&redir_lock);
return ret;
}
default: /* give up if not TCP or UDP. */
return NF_DROP;
}
}
/* Incoming packet: is it a reply to a masqueraded connection, or
part of an already-redirected TCP connection? */
void
check_for_redirect(struct sk_buff *skb)
{
struct iphdr *iph = skb->nh.iph;
struct tcphdr *tcph = (struct tcphdr *)((u_int32_t *)iph
+ iph->ihl);
struct redir *redir;
if (iph->protocol != IPPROTO_TCP)
return;
/* Must have whole header */
if (skb->len < iph->ihl*4 + sizeof(*tcph))
return;
LOCK_BH(&redir_lock);
redir = find_redir(iph->saddr, iph->daddr, tcph->source, tcph->dest);
if (redir) {
DEBUGP("Doing tcp redirect again.\n");
do_tcp_redir(skb, redir);
if (del_timer(&redir->destroyme)) {
redir->destroyme.expires = jiffies + REDIR_TIMEOUT;
add_timer(&redir->destroyme);
}
}
UNLOCK_BH(&redir_lock);
}
void
check_for_unredirect(struct sk_buff *skb)
{
struct iphdr *iph = skb->nh.iph;
struct tcphdr *tcph = (struct tcphdr *)((u_int32_t *)iph
+ iph->ihl);
struct redir *redir;
if (iph->protocol != IPPROTO_TCP)
return;
/* Must have whole header */
if (skb->len < iph->ihl*4 + sizeof(*tcph))
return;
LOCK_BH(&redir_lock);
redir = find_unredir(iph->saddr, iph->daddr, tcph->source, tcph->dest);
if (redir) {
DEBUGP("Doing tcp unredirect.\n");
do_tcp_unredir(skb, redir);
if (del_timer(&redir->destroyme)) {
redir->destroyme.expires = jiffies + REDIR_TIMEOUT;
add_timer(&redir->destroyme);
}
}
UNLOCK_BH(&redir_lock);
}
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