nf_nat_proto_tcp.c

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/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <[email protected]>
 *
 * 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/types.h>
#include <linux/init.h>
#include <linux/export.h>
#include <linux/tcp.h>

#include <linux/netfilter.h>
#include <linux/netfilter/nfnetlink_conntrack.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>

static u16 tcp_port_rover;

static void
tcp_unique_tuple(const struct nf_nat_l3proto *l3proto,
         struct nf_conntrack_tuple *tuple,
         const struct nf_nat_range *range,
         enum nf_nat_manip_type maniptype,
         const struct nf_conn *ct)
{
    nf_nat_l4proto_unique_tuple(l3proto, tuple, range, maniptype, ct,
                    &tcp_port_rover);
}

static bool
tcp_manip_pkt(struct sk_buff *skb,
          const struct nf_nat_l3proto *l3proto,
          unsigned int iphdroff, unsigned int hdroff,
          const struct nf_conntrack_tuple *tuple,
          enum nf_nat_manip_type maniptype)
{
    struct tcphdr *hdr;
    __be16 *portptr, newport, oldport;
    int hdrsize = 8; /* TCP connection tracking guarantees this much */

    /* this could be a inner header returned in icmp packet; in such
       cases we cannot update the checksum field since it is outside of
       the 8 bytes of transport layer headers we are guaranteed */
    if (skb->len >= hdroff + sizeof(struct tcphdr))
        hdrsize = sizeof(struct tcphdr);

    if (!skb_make_writable(skb, hdroff + hdrsize))
        return false;

    hdr = (struct tcphdr *)(skb->data + hdroff);

    if (maniptype == NF_NAT_MANIP_SRC) {
        /* Get rid of src port */
        newport = tuple->src.u.tcp.port;
        portptr = &hdr->source;
    } else {
        /* Get rid of dst port */
        newport = tuple->dst.u.tcp.port;
        portptr = &hdr->dest;
    }

    oldport = *portptr;
    *portptr = newport;

    if (hdrsize < sizeof(*hdr))
        return true;

    l3proto->csum_update(skb, iphdroff, &hdr->check, tuple, maniptype);
    inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, 0);
    return true;
}

const struct nf_nat_l4proto nf_nat_l4proto_tcp = {
    .l4proto        = IPPROTO_TCP,
    .manip_pkt      = tcp_manip_pkt,
    .in_range       = nf_nat_l4proto_in_range,
    .unique_tuple       = tcp_unique_tuple,
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
    .nlattr_to_range    = nf_nat_l4proto_nlattr_to_range,
#endif
};