LXR linux/net/ipv4/netfilter/nf_dup

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * (C) 2007 by Sebastian Claßen <sebastian.classen@freenet.ag>
   4 * (C) 2007-2010 by Jan Engelhardt <jengelh@medozas.de>
   5 *
   6 * Extracted from xt_TEE.c
   7 */
   8#include <linux/ip.h>
   9#include <linux/module.h>
  10#include <linux/percpu.h>
  11#include <linux/route.h>
  12#include <linux/skbuff.h>
  13#include <linux/netfilter.h>
  14#include <net/checksum.h>
  15#include <net/icmp.h>
  16#include <net/ip.h>
  17#include <net/route.h>
  18#include <net/netfilter/ipv4/nf_dup_ipv4.h>
  19#if IS_ENABLED(CONFIG_NF_CONNTRACK)
  20#include <net/netfilter/nf_conntrack.h>
  21#endif
  22
  23static bool nf_dup_ipv4_route(struct net *net, struct sk_buff *skb,
  24                              const struct in_addr *gw, int oif)
  25{
  26        const struct iphdr *iph = ip_hdr(skb);
  27        struct rtable *rt;
  28        struct flowi4 fl4;
  29
  30        memset(&fl4, 0, sizeof(fl4));
  31        if (oif != -1)
  32                fl4.flowi4_oif = oif;
  33
  34        fl4.daddr = gw->s_addr;
  35        fl4.flowi4_tos = RT_TOS(iph->tos);
  36        fl4.flowi4_scope = RT_SCOPE_UNIVERSE;
  37        fl4.flowi4_flags = FLOWI_FLAG_KNOWN_NH;
  38        rt = ip_route_output_key(net, &fl4);
  39        if (IS_ERR(rt))
  40                return false;
  41
  42        skb_dst_drop(skb);
  43        skb_dst_set(skb, &rt->dst);
  44        skb->dev      = rt->dst.dev;
  45        skb->protocol = htons(ETH_P_IP);
  46
  47        return true;
  48}
  49
  50void nf_dup_ipv4(struct net *net, struct sk_buff *skb, unsigned int hooknum,
  51                 const struct in_addr *gw, int oif)
  52{
  53        struct iphdr *iph;
  54
  55        if (this_cpu_read(nf_skb_duplicated))
  56                return;
  57        /*
  58         * Copy the skb, and route the copy. Will later return %XT_CONTINUE for
  59         * the original skb, which should continue on its way as if nothing has
  60         * happened. The copy should be independently delivered to the gateway.
  61         */
  62        skb = pskb_copy(skb, GFP_ATOMIC);
  63        if (skb == NULL)
  64                return;
  65
  66#if IS_ENABLED(CONFIG_NF_CONNTRACK)
  67        /* Avoid counting cloned packets towards the original connection. */
  68        nf_reset_ct(skb);
  69        nf_ct_set(skb, NULL, IP_CT_UNTRACKED);
  70#endif
  71        /*
  72         * If we are in PREROUTING/INPUT, decrease the TTL to mitigate potential
  73         * loops between two hosts.
  74         *
  75         * Set %IP_DF so that the original source is notified of a potentially
  76         * decreased MTU on the clone route. IPv6 does this too.
  77         *
  78         * IP header checksum will be recalculated at ip_local_out.
  79         */
  80        iph = ip_hdr(skb);
  81        iph->frag_off |= htons(IP_DF);
  82        if (hooknum == NF_INET_PRE_ROUTING ||
  83            hooknum == NF_INET_LOCAL_IN)
  84                --iph->ttl;
  85
  86        if (nf_dup_ipv4_route(net, skb, gw, oif)) {
  87                __this_cpu_write(nf_skb_duplicated, true);
  88                ip_local_out(net, skb->sk, skb);
  89                __this_cpu_write(nf_skb_duplicated, false);
  90        } else {
  91                kfree_skb(skb);
  92        }
  93}
  94EXPORT_SYMBOL_GPL(nf_dup_ipv4);
  95
  96MODULE_AUTHOR("Sebastian Claßen <sebastian.classen@freenet.ag>");
  97MODULE_AUTHOR("Jan Engelhardt <jengelh@medozas.de>");
  98MODULE_DESCRIPTION("nf_dup_ipv4: Duplicate IPv4 packet");
  99MODULE_LICENSE("GPL");
 100