// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (c) 2011 Florian Westphal <fw@strlen.de>
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*
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* based on fib_frontend.c; Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/skbuff.h>
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#include <linux/netdevice.h>
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#include <linux/ip.h>
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#include <net/ip.h>
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#include <net/ip_fib.h>
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#include <net/route.h>
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#include <linux/netfilter/xt_rpfilter.h>
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#include <linux/netfilter/x_tables.h>
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
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MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
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/* don't try to find route from mcast/bcast/zeronet */
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static __be32 rpfilter_get_saddr(__be32 addr)
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{
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if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
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ipv4_is_zeronet(addr))
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return 0;
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return addr;
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}
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static bool rpfilter_lookup_reverse(struct net *net, struct flowi4 *fl4,
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const struct net_device *dev, u8 flags)
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{
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struct fib_result res;
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int ret __maybe_unused;
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if (fib_lookup(net, fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE))
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return false;
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if (res.type != RTN_UNICAST) {
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if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
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return false;
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}
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return fib_info_nh_uses_dev(res.fi, dev) || flags & XT_RPFILTER_LOOSE;
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}
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static bool
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rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
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{
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return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
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}
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static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
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{
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const struct xt_rpfilter_info *info;
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const struct iphdr *iph;
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struct flowi4 flow;
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bool invert;
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info = par->matchinfo;
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invert = info->flags & XT_RPFILTER_INVERT;
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if (rpfilter_is_loopback(skb, xt_in(par)))
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return true ^ invert;
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iph = ip_hdr(skb);
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if (ipv4_is_zeronet(iph->saddr)) {
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if (ipv4_is_lbcast(iph->daddr) ||
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ipv4_is_local_multicast(iph->daddr))
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return true ^ invert;
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}
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memset(&flow, 0, sizeof(flow));
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flow.flowi4_iif = LOOPBACK_IFINDEX;
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flow.daddr = iph->saddr;
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flow.saddr = rpfilter_get_saddr(iph->daddr);
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flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
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flow.flowi4_tos = iph->tos & IPTOS_RT_MASK;
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flow.flowi4_scope = RT_SCOPE_UNIVERSE;
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flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));
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return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
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}
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static int rpfilter_check(const struct xt_mtchk_param *par)
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{
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const struct xt_rpfilter_info *info = par->matchinfo;
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unsigned int options = ~XT_RPFILTER_OPTION_MASK;
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if (info->flags & options) {
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pr_info_ratelimited("unknown options\n");
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return -EINVAL;
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}
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if (strcmp(par->table, "mangle") != 0 &&
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strcmp(par->table, "raw") != 0) {
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pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
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par->table);
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return -EINVAL;
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}
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return 0;
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}
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static struct xt_match rpfilter_mt_reg __read_mostly = {
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.name = "rpfilter",
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.family = NFPROTO_IPV4,
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.checkentry = rpfilter_check,
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.match = rpfilter_mt,
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.matchsize = sizeof(struct xt_rpfilter_info),
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.hooks = (1 << NF_INET_PRE_ROUTING),
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.me = THIS_MODULE
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};
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static int __init rpfilter_mt_init(void)
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{
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return xt_register_match(&rpfilter_mt_reg);
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}
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static void __exit rpfilter_mt_exit(void)
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{
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xt_unregister_match(&rpfilter_mt_reg);
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}
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module_init(rpfilter_mt_init);
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module_exit(rpfilter_mt_exit);
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