netfilter: nf_tables: add fib expression

Add FIB expression, supported for ipv4, ipv6 and inet family (the latter
just dispatches to ipv4 or ipv6 one based on nfproto).

Currently supports fetching output interface index/name and the
rtm_type associated with an address.

This can be used for adding path filtering. rtm_type is useful
to e.g. enforce a strong-end host model where packets
are only accepted if daddr is configured on the interface the
packet arrived on.

The fib expression is a native nftables alternative to the
xtables addrtype and rp_filter matches.

FIB result order for oif/oifname retrieval is as follows:
 - if packet is local (skb has rtable, RTF_LOCAL set, this
   will also catch looped-back multicast packets), set oif to
   the loopback interface.
 - if fib lookup returns an error, or result points to local,
   store zero result.  This means '--local' option of -m rpfilter
   is not supported. It is possible to use 'fib type local' or add
   explicit saddr/daddr matching rules to create exceptions if this
   is really needed.
 - store result in the destination register.
   In case of multiple routes, search set for desired oif in case
   strict matching is requested.

ipv4 and ipv6 behave fib expressions are supposed to behave the same.

[ I have collapsed Arnd Bergmann's ("netfilter: nf_tables: fib warnings")

	http://patchwork.ozlabs.org/patch/688615/

  to address fallout from this patch after rebasing nf-next, that was
  posted to address compilation warnings. --pablo ]

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 284 insertions, 0 deletions

diff --git a/net/ipv6/netfilter/Kconfig b/net/ipv6/netfilter/Kconfig
index e10a04c9cdc7..144f1de33836 100644
--- a/net/ipv6/netfilter/Kconfig
+++ b/net/ipv6/netfilter/Kconfig
@@ -54,6 +54,14 @@ config NFT_DUP_IPV6
 	help
 	  This module enables IPv6 packet duplication support for nf_tables.
 
+config NFT_FIB_IPV6
+	tristate "nf_tables fib / ipv6 route lookup support"
+	select NFT_FIB
+	help
+	  This module enables IPv6 FIB lookups, e.g. for reverse path filtering.
+	  It also allows query of the FIB for the route type, e.g. local, unicast,
+	  multicast or blackhole.
+
 endif # NF_TABLES_IPV6
 endif # NF_TABLES
 
diff --git a/net/ipv6/netfilter/Makefile b/net/ipv6/netfilter/Makefile
index b4f7d0b4e2af..7984f3071f05 100644
--- a/net/ipv6/netfilter/Makefile
+++ b/net/ipv6/netfilter/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_NFT_REJECT_IPV6) += nft_reject_ipv6.o
 obj-$(CONFIG_NFT_MASQ_IPV6) += nft_masq_ipv6.o
 obj-$(CONFIG_NFT_REDIR_IPV6) += nft_redir_ipv6.o
 obj-$(CONFIG_NFT_DUP_IPV6) += nft_dup_ipv6.o
+obj-$(CONFIG_NFT_FIB_IPV6) += nft_fib_ipv6.o
 
 # matches
 obj-$(CONFIG_IP6_NF_MATCH_AH) += ip6t_ah.o
diff --git a/net/ipv6/netfilter/nft_fib_ipv6.c b/net/ipv6/netfilter/nft_fib_ipv6.c
new file mode 100644
index 000000000000..ff1f1b6b4a4a
--- /dev/null
+++ b/net/ipv6/netfilter/nft_fib_ipv6.c
@@ -0,0 +1,275 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/netlink.h>
+#include <linux/netfilter.h>
+#include <linux/netfilter/nf_tables.h>
+#include <linux/netfilter_ipv6.h>
+#include <net/netfilter/nf_tables_core.h>
+#include <net/netfilter/nf_tables.h>
+#include <net/netfilter/nft_fib.h>
+
+#include <net/ip6_fib.h>
+#include <net/ip6_route.h>
+
+static bool fib6_is_local(const struct sk_buff *skb)
+{
+	const struct rt6_info *rt = (const void *)skb_dst(skb);
+
+	return rt && (rt->rt6i_flags & RTF_LOCAL);
+}
+
+static int get_ifindex(const struct net_device *dev)
+{
+	return dev ? dev->ifindex : 0;
+}
+
+static int nft_fib6_flowi_init(struct flowi6 *fl6, const struct nft_fib *priv,
+			       const struct nft_pktinfo *pkt,
+			       const struct net_device *dev)
+{
+	const struct ipv6hdr *iph = ipv6_hdr(pkt->skb);
+	int lookup_flags = 0;
+
+	if (priv->flags & NFTA_FIB_F_DADDR) {
+		fl6->daddr = iph->daddr;
+		fl6->saddr = iph->saddr;
+	} else {
+		fl6->daddr = iph->saddr;
+		fl6->saddr = iph->daddr;
+	}
+
+	if (ipv6_addr_type(&fl6->daddr) & IPV6_ADDR_LINKLOCAL) {
+		lookup_flags |= RT6_LOOKUP_F_IFACE;
+		fl6->flowi6_oif = get_ifindex(dev ? dev : pkt->skb->dev);
+	}
+
+	if (ipv6_addr_type(&fl6->saddr) & IPV6_ADDR_UNICAST)
+		lookup_flags |= RT6_LOOKUP_F_HAS_SADDR;
+
+	if (priv->flags & NFTA_FIB_F_MARK)
+		fl6->flowi6_mark = pkt->skb->mark;
+
+	fl6->flowlabel = (*(__be32 *)iph) & IPV6_FLOWINFO_MASK;
+
+	return lookup_flags;
+}
+
+static u32 __nft_fib6_eval_type(const struct nft_fib *priv,
+				const struct nft_pktinfo *pkt)
+{
+	const struct net_device *dev = NULL;
+	const struct nf_ipv6_ops *v6ops;
+	const struct nf_afinfo *afinfo;
+	int route_err, addrtype;
+	struct rt6_info *rt;
+	struct flowi6 fl6 = {
+		.flowi6_iif = LOOPBACK_IFINDEX,
+		.flowi6_proto = pkt->tprot,
+	};
+	u32 ret = 0;
+
+	afinfo = nf_get_afinfo(NFPROTO_IPV6);
+	if (!afinfo)
+		return RTN_UNREACHABLE;
+
+	if (priv->flags & NFTA_FIB_F_IIF)
+		dev = pkt->in;
+	else if (priv->flags & NFTA_FIB_F_OIF)
+		dev = pkt->out;
+
+	nft_fib6_flowi_init(&fl6, priv, pkt, dev);
+
+	v6ops = nf_get_ipv6_ops();
+	if (dev && v6ops && v6ops->chk_addr(pkt->net, &fl6.daddr, dev, true))
+		ret = RTN_LOCAL;
+
+	route_err = afinfo->route(pkt->net, (struct dst_entry **)&rt,
+				  flowi6_to_flowi(&fl6), false);
+	if (route_err)
+		goto err;
+
+	if (rt->rt6i_flags & RTF_REJECT) {
+		route_err = rt->dst.error;
+		dst_release(&rt->dst);
+		goto err;
+	}
+
+	if (ipv6_anycast_destination((struct dst_entry *)rt, &fl6.daddr))
+		ret = RTN_ANYCAST;
+	else if (!dev && rt->rt6i_flags & RTF_LOCAL)
+		ret = RTN_LOCAL;
+
+	dst_release(&rt->dst);
+
+	if (ret)
+		return ret;
+
+	addrtype = ipv6_addr_type(&fl6.daddr);
+
+	if (addrtype & IPV6_ADDR_MULTICAST)
+		return RTN_MULTICAST;
+	if (addrtype & IPV6_ADDR_UNICAST)
+		return RTN_UNICAST;
+
+	return RTN_UNSPEC;
+ err:
+	switch (route_err) {
+	case -EINVAL:
+		return RTN_BLACKHOLE;
+	case -EACCES:
+		return RTN_PROHIBIT;
+	case -EAGAIN:
+		return RTN_THROW;
+	default:
+		break;
+	}
+
+	return RTN_UNREACHABLE;
+}
+
+void nft_fib6_eval_type(const struct nft_expr *expr, struct nft_regs *regs,
+			const struct nft_pktinfo *pkt)
+{
+	const struct nft_fib *priv = nft_expr_priv(expr);
+	u32 *dest = &regs->data[priv->dreg];
+
+	*dest = __nft_fib6_eval_type(priv, pkt);
+}
+EXPORT_SYMBOL_GPL(nft_fib6_eval_type);
+
+void nft_fib6_eval(const struct nft_expr *expr, struct nft_regs *regs,
+		   const struct nft_pktinfo *pkt)
+{
+	const struct nft_fib *priv = nft_expr_priv(expr);
+	const struct net_device *oif = NULL;
+	u32 *dest = &regs->data[priv->dreg];
+	struct flowi6 fl6 = {
+		.flowi6_iif = LOOPBACK_IFINDEX,
+		.flowi6_proto = pkt->tprot,
+	};
+	struct rt6_info *rt;
+	int lookup_flags;
+
+	if (priv->flags & NFTA_FIB_F_IIF)
+		oif = pkt->in;
+	else if (priv->flags & NFTA_FIB_F_OIF)
+		oif = pkt->out;
+
+	lookup_flags = nft_fib6_flowi_init(&fl6, priv, pkt, oif);
+
+	if (pkt->hook == NF_INET_PRE_ROUTING && fib6_is_local(pkt->skb)) {
+		nft_fib_store_result(dest, priv->result, pkt, LOOPBACK_IFINDEX);
+		return;
+	}
+
+	*dest = 0;
+ again:
+	rt = (void *)ip6_route_lookup(pkt->net, &fl6, lookup_flags);
+	if (rt->dst.error)
+		goto put_rt_err;
+
+	/* Should not see RTF_LOCAL here */
+	if (rt->rt6i_flags & (RTF_REJECT | RTF_ANYCAST | RTF_LOCAL))
+		goto put_rt_err;
+
+	if (oif && oif != rt->rt6i_idev->dev) {
+		/* multipath route? Try again with F_IFACE */
+		if ((lookup_flags & RT6_LOOKUP_F_IFACE) == 0) {
+			lookup_flags |= RT6_LOOKUP_F_IFACE;
+			fl6.flowi6_oif = oif->ifindex;
+			ip6_rt_put(rt);
+			goto again;
+		}
+	}
+
+	switch (priv->result) {
+	case NFT_FIB_RESULT_OIF:
+		*dest = rt->rt6i_idev->dev->ifindex;
+		break;
+	case NFT_FIB_RESULT_OIFNAME:
+		strncpy((char *)dest, rt->rt6i_idev->dev->name, IFNAMSIZ);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+ put_rt_err:
+	ip6_rt_put(rt);
+}
+EXPORT_SYMBOL_GPL(nft_fib6_eval);
+
+static struct nft_expr_type nft_fib6_type;
+
+static const struct nft_expr_ops nft_fib6_type_ops = {
+	.type		= &nft_fib6_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_fib)),
+	.eval		= nft_fib6_eval_type,
+	.init		= nft_fib_init,
+	.dump		= nft_fib_dump,
+	.validate	= nft_fib_validate,
+};
+
+static const struct nft_expr_ops nft_fib6_ops = {
+	.type		= &nft_fib6_type,
+	.size		= NFT_EXPR_SIZE(sizeof(struct nft_fib)),
+	.eval		= nft_fib6_eval,
+	.init		= nft_fib_init,
+	.dump		= nft_fib_dump,
+	.validate	= nft_fib_validate,
+};
+
+static const struct nft_expr_ops *
+nft_fib6_select_ops(const struct nft_ctx *ctx,
+		    const struct nlattr * const tb[])
+{
+	enum nft_fib_result result;
+
+	if (!tb[NFTA_FIB_RESULT])
+		return ERR_PTR(-EINVAL);
+
+	result = htonl(nla_get_be32(tb[NFTA_FIB_RESULT]));
+
+	switch (result) {
+	case NFT_FIB_RESULT_OIF:
+		return &nft_fib6_ops;
+	case NFT_FIB_RESULT_OIFNAME:
+		return &nft_fib6_ops;
+	case NFT_FIB_RESULT_ADDRTYPE:
+		return &nft_fib6_type_ops;
+	default:
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+}
+
+static struct nft_expr_type nft_fib6_type __read_mostly = {
+	.name		= "fib",
+	.select_ops	= &nft_fib6_select_ops,
+	.policy		= nft_fib_policy,
+	.maxattr	= NFTA_FIB_MAX,
+	.family		= NFPROTO_IPV6,
+	.owner		= THIS_MODULE,
+};
+
+static int __init nft_fib6_module_init(void)
+{
+	return nft_register_expr(&nft_fib6_type);
+}
+
+static void __exit nft_fib6_module_exit(void)
+{
+	nft_unregister_expr(&nft_fib6_type);
+}
+module_init(nft_fib6_module_init);
+module_exit(nft_fib6_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
+MODULE_ALIAS_NFT_AF_EXPR(10, "fib");