LXR linux/net/ipv4/netfilter/nf_dup

   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
  26static 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
  53void 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        nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
  73#endif
  74        /*
  75         * If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
  76         * loops between two hosts.
  77         *
  78         * Set %IP_DF so that the original source is notified of a potentially
  79         * decreased MTU on the clone route. IPv6 does this too.
  80         *
  81         * IP header checksum will be recalculated at ip_local_out.
  82         */
  83        iph = ip_hdr(skb);
  84        iph->frag_off |= htons(IP_DF);
  85        if (hooknum == NF_INET_PRE_ROUTING ||
  86            hooknum == NF_INET_LOCAL_IN)
  87                --iph->ttl;
  88
  89        if (nf_dup_ipv4_route(net, skb, gw, oif)) {
  90                __this_cpu_write(nf_skb_duplicated, true);
  91                ip_local_out(net, skb->sk, skb);
  92                __this_cpu_write(nf_skb_duplicated, false);
  93        } else {
  94                kfree_skb(skb);
  95        }
  96}
  97EXPORT_SYMBOL_GPL(nf_dup_ipv4);
  98
  99MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
 100MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
 101MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");
 102MODULE_LICENSE("GPL");
 103