src: add fib expression

This adds the 'fib' expression which can be used to
obtain the output interface from the route table based on either
source or destination address of a packet.

This can be used to e.g. add reverse path filtering:

 # drop if not coming from the same interface packet
 # arrived on
 # nft add rule x prerouting fib saddr . iif oif eq 0 drop

 # accept only if from eth0
 # nft add rule x prerouting fib saddr . iif oif eq "eth0" accept

 # accept if from any valid interface
 # nft add rule x prerouting fib saddr oif accept

Querying of address type is also supported.  This can be used
to e.g. only accept packets to addresses configured in the same
interface:
 # fib daddr . iif type local

Its also possible to use mark and verdict map, e.g.:
 # nft add rule x prerouting meta mark set 0xdead fib daddr . mark type vmap {
   blackhole : drop,
   prohibit : drop,
   unicast : accept
 }

Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 144 insertions, 0 deletions

diff --git a/src/fib.c b/src/fib.c
new file mode 100644
index 00000000..346cce32
--- /dev/null
+++ b/src/fib.c
@@ -0,0 +1,144 @@
+/*
+ * FIB expression.
+ *
+ * Copyright (c) Red Hat GmbH.  Author: Florian Westphal <fw@strlen.de>
+ *
+ * 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 <nftables.h>
+#include <erec.h>
+#include <expression.h>
+#include <datatype.h>
+#include <gmputil.h>
+#include <utils.h>
+#include <string.h>
+#include <fib.h>
+
+#include <linux/rtnetlink.h>
+#include <net/if.h>
+
+static const char *fib_result[NFT_FIB_RESULT_MAX + 1] = {
+	[NFT_FIB_RESULT_OIF] = "oif",
+	[NFT_FIB_RESULT_OIFNAME] = "oifname",
+	[NFT_FIB_RESULT_ADDRTYPE] = "type",
+};
+
+static const struct symbol_table addrtype_tbl = {
+	.symbols	= {
+		SYMBOL("unspec",	RTN_UNSPEC),
+		SYMBOL("unicast",	RTN_UNICAST),
+		SYMBOL("local",		RTN_LOCAL),
+		SYMBOL("broadcast",	RTN_BROADCAST),
+		SYMBOL("anycast",	RTN_ANYCAST),
+		SYMBOL("multicast",	RTN_MULTICAST),
+		SYMBOL("blackhole",	RTN_BLACKHOLE),
+		SYMBOL("unreachable",	RTN_UNREACHABLE),
+		SYMBOL("prohibit",	RTN_PROHIBIT),
+		SYMBOL_LIST_END
+	}
+};
+
+static const struct datatype fib_addr_type = {
+	.type		= TYPE_FIB_ADDR,
+	.name		= "fib_addrtype",
+	.desc		= "fib address type",
+	.byteorder	= BYTEORDER_HOST_ENDIAN,
+	.size		= 4 * BITS_PER_BYTE,
+	.basetype	= &integer_type,
+	.sym_tbl	= &addrtype_tbl,
+};
+
+static const char *fib_result_str(enum nft_fib_result result)
+{
+	if (result <= NFT_FIB_RESULT_MAX)
+		return fib_result[result];
+
+	return "unknown";
+}
+
+static void __fib_expr_print_f(unsigned int *flags, unsigned int f, const char *s)
+{
+	if ((*flags & f) == 0)
+		return;
+
+	printf("%s", s);
+	*flags &= ~f;
+	if (*flags)
+		printf(" . ");
+}
+
+static void fib_expr_print(const struct expr *expr)
+{
+	unsigned int flags = expr->fib.flags;
+
+	printf("fib ");
+	__fib_expr_print_f(&flags, NFTA_FIB_F_SADDR, "saddr");
+	__fib_expr_print_f(&flags, NFTA_FIB_F_DADDR, "daddr");
+	__fib_expr_print_f(&flags, NFTA_FIB_F_MARK, "mark");
+	__fib_expr_print_f(&flags, NFTA_FIB_F_IIF, "iif");
+	__fib_expr_print_f(&flags, NFTA_FIB_F_OIF, "oif");
+
+	if (flags)
+		printf("0x%x", flags);
+
+	printf(" %s", fib_result_str(expr->fib.result));
+}
+
+static bool fib_expr_cmp(const struct expr *e1, const struct expr *e2)
+{
+	return  e1->fib.result == e2->fib.result &&
+		e1->fib.flags == e2->fib.flags;
+}
+
+static void fib_expr_clone(struct expr *new, const struct expr *expr)
+{
+	new->fib.result = expr->fib.result;
+	new->fib.flags= expr->fib.flags;
+}
+
+static const struct expr_ops fib_expr_ops = {
+	.type		= EXPR_FIB,
+	.name		= "fib",
+	.print		= fib_expr_print,
+	.cmp		= fib_expr_cmp,
+	.clone		= fib_expr_clone,
+};
+
+struct expr *fib_expr_alloc(const struct location *loc,
+			    unsigned int flags, unsigned int result)
+{
+	const struct datatype *type;
+	unsigned int len = 4 * BITS_PER_BYTE;
+	struct expr *expr;
+
+	switch (result) {
+	case NFT_FIB_RESULT_OIF:
+		type = &ifindex_type;
+		break;
+	case NFT_FIB_RESULT_OIFNAME:
+		type = &string_type;
+		len = IFNAMSIZ * BITS_PER_BYTE;
+		break;
+	case NFT_FIB_RESULT_ADDRTYPE:
+		type = &fib_addr_type;
+		break;
+	default:
+		BUG("Unknown result %d\n", result);
+	}
+
+	expr = expr_alloc(loc, &fib_expr_ops, type,
+			  BYTEORDER_HOST_ENDIAN, len);
+
+	expr->fib.result = result;
+	expr->fib.flags	= flags;
+
+	return expr;
+}
+
+static void __init fib_init(void)
+{
+	datatype_register(&fib_addr_type);
+}