net/ipv4/netfilter/nf_defrag_ipv4.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* (C) 1999-2001 Paul `Rusty' Russell
   3  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   4  */
   5
   6 #include <linux/types.h>
   7 #include <linux/ip.h>
   8 #include <linux/netfilter.h>
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <net/netns/generic.h>
  12 #include <net/route.h>
  13 #include <net/ip.h>
  14
  15 #include <linux/netfilter_bridge.h>
  16 #include <linux/netfilter_ipv4.h>
  17 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
  18 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  19 #include <net/netfilter/nf_conntrack.h>
  20 #endif
  21 #include <net/netfilter/nf_conntrack_zones.h>
  22
  23 static DEFINE_MUTEX(defrag4_mutex);
  24
  25 static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
  26                                    u_int32_t user)
  27 {
  28         int err;
  29
  30         local_bh_disable();
  31         err = ip_defrag(net, skb, user);
  32         local_bh_enable();
  33
  34         if (!err)
  35                 skb->ignore_df = 1;
  36
  37         return err;
  38 }
  39
  40 static enum ip_defrag_users nf_ct_defrag_user(unsigned int hooknum,
  41                                               struct sk_buff *skb)
  42 {
  43         u16 zone_id = NF_CT_DEFAULT_ZONE_ID;
  44 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  45         if (skb_nfct(skb)) {
  46                 enum ip_conntrack_info ctinfo;
  47                 const struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  48
  49                 zone_id = nf_ct_zone_id(nf_ct_zone(ct), CTINFO2DIR(ctinfo));
  50         }
  51 #endif
  52         if (nf_bridge_in_prerouting(skb))
  53                 return IP_DEFRAG_CONNTRACK_BRIDGE_IN + zone_id;
  54
  55         if (hooknum == NF_INET_PRE_ROUTING)
  56                 return IP_DEFRAG_CONNTRACK_IN + zone_id;
  57         else
  58                 return IP_DEFRAG_CONNTRACK_OUT + zone_id;
  59 }
  60
  61 static unsigned int ipv4_conntrack_defrag(void *priv,
  62                                           struct sk_buff *skb,
  63                                           const struct nf_hook_state *state)
  64 {
  65         struct sock *sk = skb->sk;
  66
  67         if (sk && sk_fullsock(sk) && (sk->sk_family == PF_INET) &&
  68             inet_sk(sk)->nodefrag)
  69                 return NF_ACCEPT;
  70
  71 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  72 #if !IS_ENABLED(CONFIG_NF_NAT)
  73         /* Previously seen (loopback)?  Ignore.  Do this before
  74            fragment check. */
  75         if (skb_nfct(skb) && !nf_ct_is_template((struct nf_conn *)skb_nfct(skb)))
  76                 return NF_ACCEPT;
  77 #endif
  78         if (skb->_nfct == IP_CT_UNTRACKED)
  79                 return NF_ACCEPT;
  80 #endif
  81         /* Gather fragments. */
  82         if (ip_is_fragment(ip_hdr(skb))) {
  83                 enum ip_defrag_users user =
  84                         nf_ct_defrag_user(state->hook, skb);
  85
  86                 if (nf_ct_ipv4_gather_frags(state->net, skb, user))
  87                         return NF_STOLEN;
  88         }
  89         return NF_ACCEPT;
  90 }
  91
  92 static const struct nf_hook_ops ipv4_defrag_ops[] = {
  93         {
  94                 .hook           = ipv4_conntrack_defrag,
  95                 .pf             = NFPROTO_IPV4,
  96                 .hooknum        = NF_INET_PRE_ROUTING,
  97                 .priority       = NF_IP_PRI_CONNTRACK_DEFRAG,
  98         },
  99         {
 100                 .hook           = ipv4_conntrack_defrag,
 101                 .pf             = NFPROTO_IPV4,
 102                 .hooknum        = NF_INET_LOCAL_OUT,
 103                 .priority       = NF_IP_PRI_CONNTRACK_DEFRAG,
 104         },
 105 };
 106
 107 static void __net_exit defrag4_net_exit(struct net *net)
 108 {
 109         if (net->nf.defrag_ipv4) {
 110                 nf_unregister_net_hooks(net, ipv4_defrag_ops,
 111                                         ARRAY_SIZE(ipv4_defrag_ops));
 112                 net->nf.defrag_ipv4 = false;
 113         }
 114 }
 115
 116 static struct pernet_operations defrag4_net_ops = {
 117         .exit = defrag4_net_exit,
 118 };
 119
 120 static int __init nf_defrag_init(void)
 121 {
 122         return register_pernet_subsys(&defrag4_net_ops);
 123 }
 124
 125 static void __exit nf_defrag_fini(void)
 126 {
 127         unregister_pernet_subsys(&defrag4_net_ops);
 128 }
 129
 130 int nf_defrag_ipv4_enable(struct net *net)
 131 {
 132         int err = 0;
 133
 134         might_sleep();
 135
 136         if (net->nf.defrag_ipv4)
 137                 return 0;
 138
 139         mutex_lock(&defrag4_mutex);
 140         if (net->nf.defrag_ipv4)
 141                 goto out_unlock;
 142
 143         err = nf_register_net_hooks(net, ipv4_defrag_ops,
 144                                     ARRAY_SIZE(ipv4_defrag_ops));
 145         if (err == 0)
 146                 net->nf.defrag_ipv4 = true;
 147
 148  out_unlock:
 149         mutex_unlock(&defrag4_mutex);
 150         return err;
 151 }
 152 EXPORT_SYMBOL_GPL(nf_defrag_ipv4_enable);
 153
 154 module_init(nf_defrag_init);
 155 module_exit(nf_defrag_fini);
 156
 157 MODULE_LICENSE("GPL");