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 const struct xt_table packet_mangler = {
  32         .name           = "mangle",
  33         .valid_hooks    = MANGLE_VALID_HOOKS,
  34         .me             = THIS_MODULE,
  35         .af             = NFPROTO_IPV4,
  36         .priority       = NF_IP_PRI_MANGLE,
  37 };
  38
  39 static unsigned int
  40 ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
  41 {
  42         struct net_device *out = state->out;
  43         unsigned int ret;
  44         const struct iphdr *iph;
  45         u_int8_t tos;
  46         __be32 saddr, daddr;
  47         u_int32_t mark;
  48         int err;
  49
  50         /* root is playing with raw sockets. */
  51         if (skb->len < sizeof(struct iphdr) ||
  52             ip_hdrlen(skb) < sizeof(struct iphdr))
  53                 return NF_ACCEPT;
  54
  55         /* Save things which could affect route */
  56         mark = skb->mark;
  57         iph = ip_hdr(skb);
  58         saddr = iph->saddr;
  59         daddr = iph->daddr;
  60         tos = iph->tos;
  61
  62         ret = ipt_do_table(skb, NF_INET_LOCAL_OUT, state,
  63                            dev_net(out)->ipv4.iptable_mangle);
  64         /* Reroute for ANY change. */
  65         if (ret != NF_DROP && ret != NF_STOLEN) {
  66                 iph = ip_hdr(skb);
  67
  68                 if (iph->saddr != saddr ||
  69                     iph->daddr != daddr ||
  70                     skb->mark != mark ||
  71                     iph->tos != tos) {
  72                         err = ip_route_me_harder(skb, RTN_UNSPEC);
  73                         if (err < 0)
  74                                 ret = NF_DROP_ERR(err);
  75                 }
  76         }
  77
  78         return ret;
  79 }
  80
  81 /* The work comes in here from netfilter.c. */
  82 static unsigned int
  83 iptable_mangle_hook(const struct nf_hook_ops *ops,
  84                      struct sk_buff *skb,
  85                      const struct nf_hook_state *state)
  86 {
  87         if (ops->hooknum == NF_INET_LOCAL_OUT)
  88                 return ipt_mangle_out(skb, state);
  89         if (ops->hooknum == NF_INET_POST_ROUTING)
  90                 return ipt_do_table(skb, ops->hooknum, state,
  91                                     dev_net(state->out)->ipv4.iptable_mangle);
  92         /* PREROUTING/INPUT/FORWARD: */
  93         return ipt_do_table(skb, ops->hooknum, state,
  94                             dev_net(state->in)->ipv4.iptable_mangle);
  95 }
  96
  97 static struct nf_hook_ops *mangle_ops __read_mostly;
  98
  99 static int __net_init iptable_mangle_net_init(struct net *net)
 100 {
 101         struct ipt_replace *repl;
 102
 103         repl = ipt_alloc_initial_table(&packet_mangler);
 104         if (repl == NULL)
 105                 return -ENOMEM;
 106         net->ipv4.iptable_mangle =
 107                 ipt_register_table(net, &packet_mangler, repl);
 108         kfree(repl);
 109         return PTR_ERR_OR_ZERO(net->ipv4.iptable_mangle);
 110 }
 111
 112 static void __net_exit iptable_mangle_net_exit(struct net *net)
 113 {
 114         ipt_unregister_table(net, net->ipv4.iptable_mangle);
 115 }
 116
 117 static struct pernet_operations iptable_mangle_net_ops = {
 118         .init = iptable_mangle_net_init,
 119         .exit = iptable_mangle_net_exit,
 120 };
 121
 122 static int __init iptable_mangle_init(void)
 123 {
 124         int ret;
 125
 126         ret = register_pernet_subsys(&iptable_mangle_net_ops);
 127         if (ret < 0)
 128                 return ret;
 129
 130         /* Register hooks */
 131         mangle_ops = xt_hook_link(&packet_mangler, iptable_mangle_hook);
 132         if (IS_ERR(mangle_ops)) {
 133                 ret = PTR_ERR(mangle_ops);
 134                 unregister_pernet_subsys(&iptable_mangle_net_ops);
 135         }
 136
 137         return ret;
 138 }
 139
 140 static void __exit iptable_mangle_fini(void)
 141 {
 142         xt_hook_unlink(&packet_mangler, mangle_ops);
 143         unregister_pernet_subsys(&iptable_mangle_net_ops);
 144 }
 145
 146 module_init(iptable_mangle_init);
 147 module_exit(iptable_mangle_fini);