net/ipv4/netfilter/nf_dup_ipv4.c

   1 /*
   2  * (C) 2007 by Sebastian Claßen <sebastian.classen@freenet.ag>
   3  * (C) 2007-2010 by Jan Engelhardt <jengelh@medozas.de>
   4  *
   5  * Extracted from xt_TEE.c
   6  *
   7  * This program is free software; you can redistribute it and/or modify it
   8  * under the terms of the GNU General Public License version 2 or later, as
   9  * published by the Free Software Foundation.
  10  */
  11 #include <linux/ip.h>
  12 #include <linux/module.h>
  13 #include <linux/percpu.h>
  14 #include <linux/route.h>
  15 #include <linux/skbuff.h>
  16 #include <linux/netfilter.h>
  17 #include <net/checksum.h>
  18 #include <net/icmp.h>
  19 #include <net/ip.h>
  20 #include <net/route.h>
  21 #include <net/netfilter/ipv4/nf_dup_ipv4.h>
  22 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  23 #include <net/netfilter/nf_conntrack.h>
  24 #endif
  25
  26 static bool nf_dup_ipv4_route(struct net *net, struct sk_buff *skb,
  27                               const struct in_addr *gw, int oif)
  28 {
  29         const struct iphdr *iph = ip_hdr(skb);
  30         struct rtable *rt;
  31         struct flowi4 fl4;
  32
  33         memset(&fl4, 0, sizeof(fl4));
  34         if (oif != -1)
  35                 fl4.flowi4_oif = oif;
  36
  37         fl4.daddr = gw->s_addr;
  38         fl4.flowi4_tos = RT_TOS(iph->tos);
  39         fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
  40         fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
  41         rt = ip_route_output_key(net, &fl4);
  42         if (IS_ERR(rt))
  43                 return false;
  44
  45         skb_dst_drop(skb);
  46         skb_dst_set(skb, &rt->dst);
  47         skb->dev      = rt->dst.dev;
  48         skb->protocol = htons(ETH_P_IP);
  49
  50         return true;
  51 }
  52
  53 void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
  54                  const struct in_addr *gw, int oif)
  55 {
  56         struct iphdr *iph;
  57
  58         if (this_cpu_read(nf_skb_duplicated))
  59                 return;
  60         /*
  61          * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
  62          * the original skb, which should continue on its way as if nothing has
  63          * happened. The copy should be independently delivered to the gateway.
  64          */
  65         skb = pskb_copy(skb, GFP_ATOMIC);
  66         if (skb == NULL)
  67                 return;
  68
  69 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
  70         /* Avoid counting cloned packets towards the original connection. */
  71         nf_reset(skb);
  72         skb->nfct     = &nf_ct_untracked_get()->ct_general;
  73         skb->nfctinfo = IP_CT_NEW;
  74         nf_conntrack_get(skb_nfct(skb));
  75 #endif
  76         /*
  77          * If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
  78          * loops between two hosts.
  79          *
  80          * Set %IP_DF so that the original source is notified of a potentially
  81          * decreased MTU on the clone route. IPv6 does this too.
  82          *
  83          * IP header checksum will be recalculated at ip_local_out.
  84          */
  85         iph = ip_hdr(skb);
  86         iph->frag_off |= htons(IP_DF);
  87         if (hooknum == NF_INET_PRE_ROUTING ||
  88             hooknum == NF_INET_LOCAL_IN)
  89                 --iph->ttl;
  90
  91         if (nf_dup_ipv4_route(net, skb, gw, oif)) {
  92                 __this_cpu_write(nf_skb_duplicated, true);
  93                 ip_local_out(net, skb->sk, skb);
  94                 __this_cpu_write(nf_skb_duplicated, false);
  95         } else {
  96                 kfree_skb(skb);
  97         }
  98 }
  99 EXPORT_SYMBOL_GPL(nf_dup_ipv4);
 100
 101 MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
 102 MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 103 MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");
 104 MODULE_LICENSE("GPL");