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Linux/net/ipv4/netfilter/ipt_MASQUERADE.c

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  1 /* Masquerade.  Simple mapping which alters range to a local IP address
  2    (depending on route). */
  3 
  4 /* (C) 1999-2001 Paul `Rusty' Russell
  5  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
  6  *
  7  * This program is free software; you can redistribute it and/or modify
  8  * it under the terms of the GNU General Public License version 2 as
  9  * published by the Free Software Foundation.
 10  */
 11 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 12 #include <linux/types.h>
 13 #include <linux/inetdevice.h>
 14 #include <linux/ip.h>
 15 #include <linux/timer.h>
 16 #include <linux/module.h>
 17 #include <linux/netfilter.h>
 18 #include <net/protocol.h>
 19 #include <net/ip.h>
 20 #include <net/checksum.h>
 21 #include <net/route.h>
 22 #include <linux/netfilter_ipv4.h>
 23 #include <linux/netfilter/x_tables.h>
 24 #include <net/netfilter/nf_nat.h>
 25 
 26 MODULE_LICENSE("GPL");
 27 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
 28 MODULE_DESCRIPTION("Xtables: automatic-address SNAT");
 29 
 30 /* FIXME: Multiple targets. --RR */
 31 static int masquerade_tg_check(const struct xt_tgchk_param *par)
 32 {
 33         const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;
 34 
 35         if (mr->range[0].flags & NF_NAT_RANGE_MAP_IPS) {
 36                 pr_debug("bad MAP_IPS.\n");
 37                 return -EINVAL;
 38         }
 39         if (mr->rangesize != 1) {
 40                 pr_debug("bad rangesize %u\n", mr->rangesize);
 41                 return -EINVAL;
 42         }
 43         return 0;
 44 }
 45 
 46 static unsigned int
 47 masquerade_tg(struct sk_buff *skb, const struct xt_action_param *par)
 48 {
 49         struct nf_conn *ct;
 50         struct nf_conn_nat *nat;
 51         enum ip_conntrack_info ctinfo;
 52         struct nf_nat_range newrange;
 53         const struct nf_nat_ipv4_multi_range_compat *mr;
 54         const struct rtable *rt;
 55         __be32 newsrc, nh;
 56 
 57         NF_CT_ASSERT(par->hooknum == NF_INET_POST_ROUTING);
 58 
 59         ct = nf_ct_get(skb, &ctinfo);
 60         nat = nfct_nat(ct);
 61 
 62         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
 63                             ctinfo == IP_CT_RELATED_REPLY));
 64 
 65         /* Source address is 0.0.0.0 - locally generated packet that is
 66          * probably not supposed to be masqueraded.
 67          */
 68         if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
 69                 return NF_ACCEPT;
 70 
 71         mr = par->targinfo;
 72         rt = skb_rtable(skb);
 73         nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
 74         newsrc = inet_select_addr(par->out, nh, RT_SCOPE_UNIVERSE);
 75         if (!newsrc) {
 76                 pr_info("%s ate my IP address\n", par->out->name);
 77                 return NF_DROP;
 78         }
 79 
 80         nat->masq_index = par->out->ifindex;
 81 
 82         /* Transfer from original range. */
 83         memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
 84         memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
 85         newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
 86         newrange.min_addr.ip = newsrc;
 87         newrange.max_addr.ip = newsrc;
 88         newrange.min_proto   = mr->range[0].min;
 89         newrange.max_proto   = mr->range[0].max;
 90 
 91         /* Hand modified range to generic setup. */
 92         return nf_nat_setup_info(ct, &newrange, NF_NAT_MANIP_SRC);
 93 }
 94 
 95 static int
 96 device_cmp(struct nf_conn *i, void *ifindex)
 97 {
 98         const struct nf_conn_nat *nat = nfct_nat(i);
 99 
100         if (!nat)
101                 return 0;
102         if (nf_ct_l3num(i) != NFPROTO_IPV4)
103                 return 0;
104         return nat->masq_index == (int)(long)ifindex;
105 }
106 
107 static int masq_device_event(struct notifier_block *this,
108                              unsigned long event,
109                              void *ptr)
110 {
111         const struct net_device *dev = netdev_notifier_info_to_dev(ptr);
112         struct net *net = dev_net(dev);
113 
114         if (event == NETDEV_DOWN) {
115                 /* Device was downed.  Search entire table for
116                    conntracks which were associated with that device,
117                    and forget them. */
118                 NF_CT_ASSERT(dev->ifindex != 0);
119 
120                 nf_ct_iterate_cleanup(net, device_cmp,
121                                       (void *)(long)dev->ifindex, 0, 0);
122         }
123 
124         return NOTIFY_DONE;
125 }
126 
127 static int masq_inet_event(struct notifier_block *this,
128                            unsigned long event,
129                            void *ptr)
130 {
131         struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
132         struct netdev_notifier_info info;
133 
134         netdev_notifier_info_init(&info, dev);
135         return masq_device_event(this, event, &info);
136 }
137 
138 static struct notifier_block masq_dev_notifier = {
139         .notifier_call  = masq_device_event,
140 };
141 
142 static struct notifier_block masq_inet_notifier = {
143         .notifier_call  = masq_inet_event,
144 };
145 
146 static struct xt_target masquerade_tg_reg __read_mostly = {
147         .name           = "MASQUERADE",
148         .family         = NFPROTO_IPV4,
149         .target         = masquerade_tg,
150         .targetsize     = sizeof(struct nf_nat_ipv4_multi_range_compat),
151         .table          = "nat",
152         .hooks          = 1 << NF_INET_POST_ROUTING,
153         .checkentry     = masquerade_tg_check,
154         .me             = THIS_MODULE,
155 };
156 
157 static int __init masquerade_tg_init(void)
158 {
159         int ret;
160 
161         ret = xt_register_target(&masquerade_tg_reg);
162 
163         if (ret == 0) {
164                 /* Register for device down reports */
165                 register_netdevice_notifier(&masq_dev_notifier);
166                 /* Register IP address change reports */
167                 register_inetaddr_notifier(&masq_inet_notifier);
168         }
169 
170         return ret;
171 }
172 
173 static void __exit masquerade_tg_exit(void)
174 {
175         xt_unregister_target(&masquerade_tg_reg);
176         unregister_netdevice_notifier(&masq_dev_notifier);
177         unregister_inetaddr_notifier(&masq_inet_notifier);
178 }
179 
180 module_init(masquerade_tg_init);
181 module_exit(masquerade_tg_exit);
182 

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