![Andy Gospodarek](/assets/img/avatar_default.png)
This feature is only enabled with the new per-interface or ipv4 global sysctls called 'ignore_routes_with_linkdown'. net.ipv4.conf.all.ignore_routes_with_linkdown = 0 net.ipv4.conf.default.ignore_routes_with_linkdown = 0 net.ipv4.conf.lo.ignore_routes_with_linkdown = 0 ... When the above sysctls are set, will report to userspace that a route is dead and will no longer resolve to this nexthop when performing a fib lookup. This will signal to userspace that the route will not be selected. The signalling of a RTNH_F_DEAD is only passed to userspace if the sysctl is enabled and link is down. This was done as without it the netlink listeners would have no idea whether or not a nexthop would be selected. The kernel only sets RTNH_F_DEAD internally if the interface has IFF_UP cleared. With the new sysctl set, the following behavior can be observed (interface p8p1 is link-down): default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 dead linkdown 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 dead linkdown 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 90.0.0.1 via 70.0.0.2 dev p7p1 src 70.0.0.1 cache local 80.0.0.1 dev lo src 80.0.0.1 cache <local> 80.0.0.2 via 10.0.5.2 dev p9p1 src 10.0.5.15 cache While the route does remain in the table (so it can be modified if needed rather than being wiped away as it would be if IFF_UP was cleared), the proper next-hop is chosen automatically when the link is down. Now interface p8p1 is linked-up: default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 192.168.56.0/24 dev p2p1 proto kernel scope link src 192.168.56.2 90.0.0.1 via 80.0.0.2 dev p8p1 src 80.0.0.1 cache local 80.0.0.1 dev lo src 80.0.0.1 cache <local> 80.0.0.2 dev p8p1 src 80.0.0.1 cache and the output changes to what one would expect. If the sysctl is not set, the following output would be expected when p8p1 is down: default via 10.0.5.2 dev p9p1 10.0.5.0/24 dev p9p1 proto kernel scope link src 10.0.5.15 70.0.0.0/24 dev p7p1 proto kernel scope link src 70.0.0.1 80.0.0.0/24 dev p8p1 proto kernel scope link src 80.0.0.1 linkdown 90.0.0.0/24 via 80.0.0.2 dev p8p1 metric 1 linkdown 90.0.0.0/24 via 70.0.0.2 dev p7p1 metric 2 Since the dead flag does not appear, there should be no expectation that the kernel would skip using this route due to link being down. v2: Split kernel changes into 2 patches, this actually makes a behavioral change if the sysctl is set. Also took suggestion from Alex to simplify code by only checking sysctl during fib lookup and suggestion from Scott to add a per-interface sysctl. v3: Code clean-ups to make it more readable and efficient as well as a reverse path check fix. v4: Drop binary sysctl v5: Whitespace fixups from Dave v6: Style changes from Dave and checkpatch suggestions v7: One more checkpatch fixup Signed-off-by: Andy Gospodarek <gospo@cumulusnetworks.com> Signed-off-by: Dinesh Dutt <ddutt@cumulusnetworks.com> Acked-by: Scott Feldman <sfeldma@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
145 lines
3.6 KiB
C
145 lines
3.6 KiB
C
/*
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* Copyright (c) 2011 Florian Westphal <fw@strlen.de>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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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 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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bool dev_match;
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struct net *net = dev_net(dev);
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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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dev_match = false;
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#ifdef CONFIG_IP_ROUTE_MULTIPATH
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for (ret = 0; ret < res.fi->fib_nhs; ret++) {
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struct fib_nh *nh = &res.fi->fib_nh[ret];
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if (nh->nh_dev == dev) {
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dev_match = true;
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break;
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}
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}
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#else
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if (FIB_RES_DEV(res) == dev)
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dev_match = true;
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#endif
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if (dev_match || flags & XT_RPFILTER_LOOSE)
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return FIB_RES_NH(res).nh_scope <= RT_SCOPE_HOST;
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return dev_match;
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}
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static bool rpfilter_is_local(const struct sk_buff *skb)
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{
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const struct rtable *rt = skb_rtable(skb);
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return rt && (rt->rt_flags & RTCF_LOCAL);
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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_local(skb))
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return true ^ invert;
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iph = ip_hdr(skb);
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if (ipv4_is_multicast(iph->daddr)) {
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if (ipv4_is_zeronet(iph->saddr))
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return ipv4_is_local_multicast(iph->daddr) ^ invert;
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}
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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_oif = 0;
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flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
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flow.flowi4_tos = RT_TOS(iph->tos);
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flow.flowi4_scope = RT_SCOPE_UNIVERSE;
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return rpfilter_lookup_reverse(&flow, par->in, 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("unknown options encountered");
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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("match only valid in the \'raw\' "
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"or \'mangle\' tables, not \'%s\'.\n", 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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