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/rcupdate.h>
  11 #include <linux/skbuff.h>
  12 #include <net/netns/generic.h>
  13 #include <net/route.h>
  14 #include <net/ip.h>
  15
  16 #include <linux/netfilter_bridge.h>
  17 #include <linux/netfilter_ipv4.h>
  18 #include <net/netfilter/ipv4/nf_defrag_ipv4.h>
  19 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  20 #include <net/netfilter/nf_conntrack.h>
  21 #endif
  22 #include <net/netfilter/nf_conntrack_zones.h>
  23
  24 static DEFINE_MUTEX(defrag4_mutex);
  25
  26 static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
  27                                    u_int32_t user)
  28 {
  29         int err;
  30
  31         local_bh_disable();
  32         err = ip_defrag(net, skb, user);
  33         local_bh_enable();
  34
  35         if (!err)
  36                 skb->ignore_df = 1;
  37
  38         return err;
  39 }
  40
  41 static enum ip_defrag_users nf_ct_defrag_user(unsigned int hooknum,
  42                                               struct sk_buff *skb)
  43 {
  44         u16 zone_id = NF_CT_DEFAULT_ZONE_ID;
  45 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  46         if (skb_nfct(skb)) {
  47                 enum ip_conntrack_info ctinfo;
  48                 const struct nf_conn *ct = nf_ct_get(skb, &ctinfo);
  49
  50                 zone_id = nf_ct_zone_id(nf_ct_zone(ct), CTINFO2DIR(ctinfo));
  51         }
  52 #endif
  53         if (nf_bridge_in_prerouting(skb))
  54                 return IP_DEFRAG_CONNTRACK_BRIDGE_IN + zone_id;
  55
  56         if (hooknum == NF_INET_PRE_ROUTING)
  57                 return IP_DEFRAG_CONNTRACK_IN + zone_id;
  58         else
  59                 return IP_DEFRAG_CONNTRACK_OUT + zone_id;
  60 }
  61
  62 static unsigned int ipv4_conntrack_defrag(void *priv,
  63                                           struct sk_buff *skb,
  64                                           const struct nf_hook_state *state)
  65 {
  66         struct sock *sk = skb->sk;
  67
  68         if (sk && sk_fullsock(sk) && (sk->sk_family == PF_INET) &&
  69             inet_test_bit(NODEFRAG, sk))
  70                 return NF_ACCEPT;
  71
  72 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  73 #if !IS_ENABLED(CONFIG_NF_NAT)
  74         /* Previously seen (loopback)?  Ignore.  Do this before
  75            fragment check. */
  76         if (skb_nfct(skb) && !nf_ct_is_template((struct nf_conn *)skb_nfct(skb)))
  77                 return NF_ACCEPT;
  78 #endif
  79         if (skb->_nfct == IP_CT_UNTRACKED)
  80                 return NF_ACCEPT;
  81 #endif
  82         /* Gather fragments. */
  83         if (ip_is_fragment(ip_hdr(skb))) {
  84                 enum ip_defrag_users user =
  85                         nf_ct_defrag_user(state->hook, skb);
  86
  87                 if (nf_ct_ipv4_gather_frags(state->net, skb, user))
  88                         return NF_STOLEN;
  89         }
  90         return NF_ACCEPT;
  91 }
  92
  93 static const struct nf_hook_ops ipv4_defrag_ops[] = {
  94         {
  95                 .hook           = ipv4_conntrack_defrag,
  96                 .pf             = NFPROTO_IPV4,
  97                 .hooknum        = NF_INET_PRE_ROUTING,
  98                 .priority       = NF_IP_PRI_CONNTRACK_DEFRAG,
  99         },
 100         {
 101                 .hook           = ipv4_conntrack_defrag,
 102                 .pf             = NFPROTO_IPV4,
 103                 .hooknum        = NF_INET_LOCAL_OUT,
 104                 .priority       = NF_IP_PRI_CONNTRACK_DEFRAG,
 105         },
 106 };
 107
 108 static void __net_exit defrag4_net_exit(struct net *net)
 109 {
 110         if (net->nf.defrag_ipv4_users) {
 111                 nf_unregister_net_hooks(net, ipv4_defrag_ops,
 112                                         ARRAY_SIZE(ipv4_defrag_ops));
 113                 net->nf.defrag_ipv4_users = 0;
 114         }
 115 }
 116
 117 static const struct nf_defrag_hook defrag_hook = {
 118         .owner = THIS_MODULE,
 119         .enable = nf_defrag_ipv4_enable,
 120         .disable = nf_defrag_ipv4_disable,
 121 };
 122
 123 static struct pernet_operations defrag4_net_ops = {
 124         .exit = defrag4_net_exit,
 125 };
 126
 127 static int __init nf_defrag_init(void)
 128 {
 129         int err;
 130
 131         err = register_pernet_subsys(&defrag4_net_ops);
 132         if (err)
 133                 return err;
 134
 135         rcu_assign_pointer(nf_defrag_v4_hook, &defrag_hook);
 136         return err;
 137 }
 138
 139 static void __exit nf_defrag_fini(void)
 140 {
 141         rcu_assign_pointer(nf_defrag_v4_hook, NULL);
 142         unregister_pernet_subsys(&defrag4_net_ops);
 143 }
 144
 145 int nf_defrag_ipv4_enable(struct net *net)
 146 {
 147         int err = 0;
 148
 149         mutex_lock(&defrag4_mutex);
 150         if (net->nf.defrag_ipv4_users == UINT_MAX) {
 151                 err = -EOVERFLOW;
 152                 goto out_unlock;
 153         }
 154
 155         if (net->nf.defrag_ipv4_users) {
 156                 net->nf.defrag_ipv4_users++;
 157                 goto out_unlock;
 158         }
 159
 160         err = nf_register_net_hooks(net, ipv4_defrag_ops,
 161                                     ARRAY_SIZE(ipv4_defrag_ops));
 162         if (err == 0)
 163                 net->nf.defrag_ipv4_users = 1;
 164
 165  out_unlock:
 166         mutex_unlock(&defrag4_mutex);
 167         return err;
 168 }
 169 EXPORT_SYMBOL_GPL(nf_defrag_ipv4_enable);
 170
 171 void nf_defrag_ipv4_disable(struct net *net)
 172 {
 173         mutex_lock(&defrag4_mutex);
 174         if (net->nf.defrag_ipv4_users) {
 175                 net->nf.defrag_ipv4_users--;
 176                 if (net->nf.defrag_ipv4_users == 0)
 177                         nf_unregister_net_hooks(net, ipv4_defrag_ops,
 178                                                 ARRAY_SIZE(ipv4_defrag_ops));
 179         }
 180
 181         mutex_unlock(&defrag4_mutex);
 182 }
 183 EXPORT_SYMBOL_GPL(nf_defrag_ipv4_disable);
 184
 185 module_init(nf_defrag_init);
 186 module_exit(nf_defrag_fini);
 187
 188 MODULE_LICENSE("GPL");
 189 MODULE_DESCRIPTION("IPv4 defragmentation support");