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Linux/net/ipv4/netfilter/iptable_mangle.c

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  1 // SPDX-License-Identifier: GPL-2.0-only
  2 /*
  3  * This is the 1999 rewrite of IP Firewalling, aiming for kernel 2.3.x.
  4  *
  5  * Copyright (C) 1999 Paul `Rusty' Russell & Michael J. Neuling
  6  * Copyright (C) 2000-2004 Netfilter Core Team <coreteam@netfilter.org>
  7  */
  8 #include <linux/module.h>
  9 #include <linux/netfilter_ipv4/ip_tables.h>
 10 #include <linux/netdevice.h>
 11 #include <linux/skbuff.h>
 12 #include <linux/slab.h>
 13 #include <net/sock.h>
 14 #include <net/route.h>
 15 #include <linux/ip.h>
 16 #include <net/ip.h>
 17 
 18 MODULE_LICENSE("GPL");
 19 MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
 20 MODULE_DESCRIPTION("iptables mangle table");
 21 
 22 #define MANGLE_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
 23                             (1 << NF_INET_LOCAL_IN) | \
 24                             (1 << NF_INET_FORWARD) | \
 25                             (1 << NF_INET_LOCAL_OUT) | \
 26                             (1 << NF_INET_POST_ROUTING))
 27 
 28 static int __net_init iptable_mangle_table_init(struct net *net);
 29 
 30 static const struct xt_table packet_mangler = {
 31         .name           = "mangle",
 32         .valid_hooks    = MANGLE_VALID_HOOKS,
 33         .me             = THIS_MODULE,
 34         .af             = NFPROTO_IPV4,
 35         .priority       = NF_IP_PRI_MANGLE,
 36         .table_init     = iptable_mangle_table_init,
 37 };
 38 
 39 static unsigned int
 40 ipt_mangle_out(struct sk_buff *skb, const struct nf_hook_state *state)
 41 {
 42         unsigned int ret;
 43         const struct iphdr *iph;
 44         u_int8_t tos;
 45         __be32 saddr, daddr;
 46         u_int32_t mark;
 47         int err;
 48 
 49         /* Save things which could affect route */
 50         mark = skb->mark;
 51         iph = ip_hdr(skb);
 52         saddr = iph->saddr;
 53         daddr = iph->daddr;
 54         tos = iph->tos;
 55 
 56         ret = ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
 57         /* Reroute for ANY change. */
 58         if (ret != NF_DROP && ret != NF_STOLEN) {
 59                 iph = ip_hdr(skb);
 60 
 61                 if (iph->saddr != saddr ||
 62                     iph->daddr != daddr ||
 63                     skb->mark != mark ||
 64                     iph->tos != tos) {
 65                         err = ip_route_me_harder(state->net, skb, RTN_UNSPEC);
 66                         if (err < 0)
 67                                 ret = NF_DROP_ERR(err);
 68                 }
 69         }
 70 
 71         return ret;
 72 }
 73 
 74 /* The work comes in here from netfilter.c. */
 75 static unsigned int
 76 iptable_mangle_hook(void *priv,
 77                      struct sk_buff *skb,
 78                      const struct nf_hook_state *state)
 79 {
 80         if (state->hook == NF_INET_LOCAL_OUT)
 81                 return ipt_mangle_out(skb, state);
 82         return ipt_do_table(skb, state, state->net->ipv4.iptable_mangle);
 83 }
 84 
 85 static struct nf_hook_ops *mangle_ops __read_mostly;
 86 static int __net_init iptable_mangle_table_init(struct net *net)
 87 {
 88         struct ipt_replace *repl;
 89         int ret;
 90 
 91         if (net->ipv4.iptable_mangle)
 92                 return 0;
 93 
 94         repl = ipt_alloc_initial_table(&packet_mangler);
 95         if (repl == NULL)
 96                 return -ENOMEM;
 97         ret = ipt_register_table(net, &packet_mangler, repl, mangle_ops,
 98                                  &net->ipv4.iptable_mangle);
 99         kfree(repl);
100         return ret;
101 }
102 
103 static void __net_exit iptable_mangle_net_exit(struct net *net)
104 {
105         if (!net->ipv4.iptable_mangle)
106                 return;
107         ipt_unregister_table(net, net->ipv4.iptable_mangle, mangle_ops);
108         net->ipv4.iptable_mangle = NULL;
109 }
110 
111 static struct pernet_operations iptable_mangle_net_ops = {
112         .exit = iptable_mangle_net_exit,
113 };
114 
115 static int __init iptable_mangle_init(void)
116 {
117         int ret;
118 
119         mangle_ops = xt_hook_ops_alloc(&packet_mangler, iptable_mangle_hook);
120         if (IS_ERR(mangle_ops)) {
121                 ret = PTR_ERR(mangle_ops);
122                 return ret;
123         }
124 
125         ret = register_pernet_subsys(&iptable_mangle_net_ops);
126         if (ret < 0) {
127                 kfree(mangle_ops);
128                 return ret;
129         }
130 
131         ret = iptable_mangle_table_init(&init_net);
132         if (ret) {
133                 unregister_pernet_subsys(&iptable_mangle_net_ops);
134                 kfree(mangle_ops);
135         }
136 
137         return ret;
138 }
139 
140 static void __exit iptable_mangle_fini(void)
141 {
142         unregister_pernet_subsys(&iptable_mangle_net_ops);
143         kfree(mangle_ops);
144 }
145 
146 module_init(iptable_mangle_init);
147 module_exit(iptable_mangle_fini);
148 

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