This patch adds support to NAT to randomize source ports. Signed-off-by: Eric Leblond <eric@inl.fr> Signed-off-by: Patrick McHardy <kaber@trash.net> Signed-off-by: David S. Miller <davem@davemloft.net>
155 lines
4.2 KiB
C
155 lines
4.2 KiB
C
/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#include <linux/types.h>
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#include <linux/init.h>
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#include <linux/random.h>
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#include <linux/netfilter.h>
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#include <linux/ip.h>
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#include <linux/tcp.h>
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#include <linux/if.h>
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#include <linux/netfilter/nfnetlink_conntrack.h>
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#include <linux/netfilter_ipv4/ip_nat.h>
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#include <linux/netfilter_ipv4/ip_nat_rule.h>
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#include <linux/netfilter_ipv4/ip_nat_protocol.h>
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#include <linux/netfilter_ipv4/ip_nat_core.h>
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static int
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tcp_in_range(const struct ip_conntrack_tuple *tuple,
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enum ip_nat_manip_type maniptype,
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const union ip_conntrack_manip_proto *min,
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const union ip_conntrack_manip_proto *max)
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{
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__be16 port;
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if (maniptype == IP_NAT_MANIP_SRC)
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port = tuple->src.u.tcp.port;
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else
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port = tuple->dst.u.tcp.port;
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return ntohs(port) >= ntohs(min->tcp.port)
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&& ntohs(port) <= ntohs(max->tcp.port);
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}
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static int
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tcp_unique_tuple(struct ip_conntrack_tuple *tuple,
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const struct ip_nat_range *range,
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enum ip_nat_manip_type maniptype,
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const struct ip_conntrack *conntrack)
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{
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static u_int16_t port;
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__be16 *portptr;
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unsigned int range_size, min, i;
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if (maniptype == IP_NAT_MANIP_SRC)
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portptr = &tuple->src.u.tcp.port;
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else
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portptr = &tuple->dst.u.tcp.port;
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/* If no range specified... */
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if (!(range->flags & IP_NAT_RANGE_PROTO_SPECIFIED)) {
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/* If it's dst rewrite, can't change port */
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if (maniptype == IP_NAT_MANIP_DST)
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return 0;
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/* Map privileged onto privileged. */
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if (ntohs(*portptr) < 1024) {
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/* Loose convention: >> 512 is credential passing */
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if (ntohs(*portptr)<512) {
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min = 1;
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range_size = 511 - min + 1;
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} else {
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min = 600;
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range_size = 1023 - min + 1;
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}
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} else {
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min = 1024;
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range_size = 65535 - 1024 + 1;
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}
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} else {
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min = ntohs(range->min.tcp.port);
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range_size = ntohs(range->max.tcp.port) - min + 1;
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}
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/* Start from random port to avoid prediction */
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if (range->flags & IP_NAT_RANGE_PROTO_RANDOM)
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port = net_random();
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for (i = 0; i < range_size; i++, port++) {
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*portptr = htons(min + port % range_size);
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if (!ip_nat_used_tuple(tuple, conntrack)) {
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return 1;
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}
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}
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return 0;
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}
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static int
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tcp_manip_pkt(struct sk_buff **pskb,
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unsigned int iphdroff,
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const struct ip_conntrack_tuple *tuple,
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enum ip_nat_manip_type maniptype)
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{
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struct iphdr *iph = (struct iphdr *)((*pskb)->data + iphdroff);
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struct tcphdr *hdr;
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unsigned int hdroff = iphdroff + iph->ihl*4;
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__be32 oldip, newip;
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__be16 *portptr, newport, oldport;
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int hdrsize = 8; /* TCP connection tracking guarantees this much */
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/* this could be a inner header returned in icmp packet; in such
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cases we cannot update the checksum field since it is outside of
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the 8 bytes of transport layer headers we are guaranteed */
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if ((*pskb)->len >= hdroff + sizeof(struct tcphdr))
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hdrsize = sizeof(struct tcphdr);
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if (!skb_make_writable(pskb, hdroff + hdrsize))
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return 0;
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iph = (struct iphdr *)((*pskb)->data + iphdroff);
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hdr = (struct tcphdr *)((*pskb)->data + hdroff);
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if (maniptype == IP_NAT_MANIP_SRC) {
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/* Get rid of src ip and src pt */
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oldip = iph->saddr;
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newip = tuple->src.ip;
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newport = tuple->src.u.tcp.port;
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portptr = &hdr->source;
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} else {
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/* Get rid of dst ip and dst pt */
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oldip = iph->daddr;
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newip = tuple->dst.ip;
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newport = tuple->dst.u.tcp.port;
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portptr = &hdr->dest;
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}
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oldport = *portptr;
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*portptr = newport;
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if (hdrsize < sizeof(*hdr))
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return 1;
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nf_proto_csum_replace4(&hdr->check, *pskb, oldip, newip, 1);
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nf_proto_csum_replace2(&hdr->check, *pskb, oldport, newport, 0);
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return 1;
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}
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struct ip_nat_protocol ip_nat_protocol_tcp = {
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.name = "TCP",
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.protonum = IPPROTO_TCP,
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.me = THIS_MODULE,
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.manip_pkt = tcp_manip_pkt,
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.in_range = tcp_in_range,
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.unique_tuple = tcp_unique_tuple,
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#if defined(CONFIG_IP_NF_CONNTRACK_NETLINK) || \
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defined(CONFIG_IP_NF_CONNTRACK_NETLINK_MODULE)
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.range_to_nfattr = ip_nat_port_range_to_nfattr,
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.nfattr_to_range = ip_nat_port_nfattr_to_range,
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#endif
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};
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