net/ipv4/netfilter/iptable_mangle.c

   1 /*
   2  * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
   3  *
   4  * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
   5  * Copyright (C) 2000-2004 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 #include <linux/module.h>
  12 #include <linux/netfilter_ipv4/ip_tables.h>
  13 #include <linux/netdevice.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/slab.h>
  16 #include <net/sock.h>
  17 #include <net/route.h>
  18 #include <linux/ip.h>
  19 #include <net/ip.h>
  20
  21 MODULE_LICENSE("GPL");
  22 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
  23 MODULE_DESCRIPTION("iptables mangle table");
  24
  25 #define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
  26                             (1 << NF_INET_LOCAL_IN) | \
  27                             (1 << NF_INET_FORWARD) | \
  28                             (1 << NF_INET_LOCAL_OUT) | \
  29                             (1 << NF_INET_POST_ROUTING))
  30
  31 static int __net_init iptable_mangle_table_init(struct net *net);
  32
  33 static const struct xt_table packet_mangler = {
  34         .name           = "mangle",
  35         .valid_hooks    = MANGLE_VALID_HOOKS,
  36         .me             = THIS_MODULE,
  37         .af             = NFPROTO_IPV4,
  38         .priority       = NF_IP_PRI_MANGLE,
  39         .table_init     = iptable_mangle_table_init,
  40 };
  41
  42 static unsigned int
  43 ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
  44 {
  45         unsigned int ret;
  46         const struct iphdr *iph;
  47         u_int8_t tos;
  48         __be32 saddr, daddr;
  49         u_int32_t mark;
  50         int err;
  51
  52         /* root is playing with raw sockets. */
  53         if (skb->len < sizeof(struct iphdr) ||
  54             ip_hdrlen(skb) < sizeof(struct iphdr))
  55                 return NF_ACCEPT;
  56
  57         /* Save things which could affect route */
  58         mark = skb->mark;
  59         iph = ip_hdr(skb);
  60         saddr = iph->saddr;
  61         daddr = iph->daddr;
  62         tos = iph->tos;
  63
  64         ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
  65         /* Reroute for ANY change. */
  66         if (ret != NF_DROP && ret != NF_STOLEN) {
  67                 iph = ip_hdr(skb);
  68
  69                 if (iph->saddr != saddr ||
  70                     iph->daddr != daddr ||
  71                     skb->mark != mark ||
  72                     iph->tos != tos) {
  73                         err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
  74                         if (err < 0)
  75                                 ret = NF_DROP_ERR(err);
  76                 }
  77         }
  78
  79         return ret;
  80 }
  81
  82 /* The work comes in here from netfilter.c. */
  83 static unsigned int
  84 iptable_mangle_hook(void *priv,
  85                      struct sk_buff *skb,
  86                      const struct nf_hook_state *state)
  87 {
  88         if (state->hook == NF_INET_LOCAL_OUT)
  89                 return ipt_mangle_out(skb, state);
  90         if (state->hook == NF_INET_POST_ROUTING)
  91                 return ipt_do_table(skb, state,
  92                                     state->net->ipv4.iptable_mangle);
  93         /* PREROUTING/INPUT/FORWARD: */
  94         return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
  95 }
  96
  97 static struct nf_hook_ops *mangle_ops __read_mostly;
  98 static int __net_init iptable_mangle_table_init(struct net *net)
  99 {
 100         struct ipt_replace *repl;
 101         int ret;
 102
 103         if (net->ipv4.iptable_mangle)
 104                 return 0;
 105
 106         repl = ipt_alloc_initial_table(&packet_mangler);
 107         if (repl == NULL)
 108                 return -ENOMEM;
 109         ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops,
 110                                  &net->ipv4.iptable_mangle);
 111         kfree(repl);
 112         return ret;
 113 }
 114
 115 static void __net_exit iptable_mangle_net_exit(struct net *net)
 116 {
 117         if (!net->ipv4.iptable_mangle)
 118                 return;
 119         ipt_unregister_table(net, net->ipv4.iptable_mangle, mangle_ops);
 120         net->ipv4.iptable_mangle = NULL;
 121 }
 122
 123 static struct pernet_operations iptable_mangle_net_ops = {
 124         .exit = iptable_mangle_net_exit,
 125 };
 126
 127 static int __init iptable_mangle_init(void)
 128 {
 129         int ret;
 130
 131         mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
 132         if (IS_ERR(mangle_ops)) {
 133                 ret = PTR_ERR(mangle_ops);
 134                 return ret;
 135         }
 136
 137         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 138         if (ret < 0) {
 139                 kfree(mangle_ops);
 140                 return ret;
 141         }
 142
 143         ret = iptable_mangle_table_init(&init_net);
 144         if (ret) {
 145                 unregister_pernet_subsys(&iptable_mangle_net_ops);
 146                 kfree(mangle_ops);
 147         }
 148
 149         return ret;
 150 }
 151
 152 static void __exit iptable_mangle_fini(void)
 153 {
 154         unregister_pernet_subsys(&iptable_mangle_net_ops);
 155         kfree(mangle_ops);
 156 }
 157
 158 module_init(iptable_mangle_init);
 159 module_exit(iptable_mangle_fini);