nf_nat_proto_udp.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/export.h>
#include <linux/init.h>
#include <linux/udp.h>

#include <linux/netfilter.h>
#include <net/netfilter/nf_nat.h>
#include <net/netfilter/nf_nat_core.h>
#include <net/netfilter/nf_nat_l3proto.h>
#include <net/netfilter/nf_nat_l4proto.h>

static u16 udp_port_rover;

static void
udp_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,
                    &udp_port_rover);
}

static bool
udp_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 udphdr *hdr;
    __be16 *portptr, newport;

    if (!skb_make_writable(skb, hdroff + sizeof(*hdr)))
        return false;
    hdr = (struct udphdr *)(skb->data + hdroff);

    if (maniptype == NF_NAT_MANIP_SRC) {
        /* Get rid of src port */
        newport = tuple->src.u.udp.port;
        portptr = &hdr->source;
    } else {
        /* Get rid of dst port */
        newport = tuple->dst.u.udp.port;
        portptr = &hdr->dest;
    }
    if (hdr->check || skb->ip_summed == CHECKSUM_PARTIAL) {
        l3proto->csum_update(skb, iphdroff, &hdr->check,
                     tuple, maniptype);
        inet_proto_csum_replace2(&hdr->check, skb, *portptr, newport,
                     0);
        if (!hdr->check)
            hdr->check = CSUM_MANGLED_0;
    }
    *portptr = newport;
    return true;
}

const struct nf_nat_l4proto nf_nat_l4proto_udp = {
    .l4proto        = IPPROTO_UDP,
    .manip_pkt      = udp_manip_pkt,
    .in_range       = nf_nat_l4proto_in_range,
    .unique_tuple       = udp_unique_tuple,
#if defined(CONFIG_NF_CT_NETLINK) || defined(CONFIG_NF_CT_NETLINK_MODULE)
    .nlattr_to_range    = nf_nat_l4proto_nlattr_to_range,
#endif
};