linux/net/ipv4/netfilter/nf_defrag_ipv4.c
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   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
  23static DEFINE_MUTEX(defrag4_mutex);
  24
  25static 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
  40static 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
  61static 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
  92static 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
 107static 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
 116static struct pernet_operations defrag4_net_ops = {
 117        .exit = defrag4_net_exit,
 118};
 119
 120static int __init nf_defrag_init(void)
 121{
 122        return register_pernet_subsys(&defrag4_net_ops);
 123}
 124
 125static void __exit nf_defrag_fini(void)
 126{
 127        unregister_pernet_subsys(&defrag4_net_ops);
 128}
 129
 130int 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}
 152EXPORT_SYMBOL_GPL(nf_defrag_ipv4_enable);
 153
 154module_init(nf_defrag_init);
 155module_exit(nf_defrag_fini);
 156
 157MODULE_LICENSE("GPL");
 158