[PATCH 2/3 WIP nf-next] netfilter: implement Passive OS fingerprint module in nft_osf

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Add basic module functions into nft_osf.[ch] in order to start the
implementation of OSF module in nf_tables.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@xxxxxxxxxx>
---
 include/uapi/linux/netfilter/nf_tables.h |  10 ++
 net/netfilter/Kconfig                    |   6 ++
 net/netfilter/Makefile                   |   1 +
 net/netfilter/nft_osf.c                  | 118 +++++++++++++++++++++++
 4 files changed, 135 insertions(+)
 create mode 100644 net/netfilter/nft_osf.c

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 89438e68dc03..48061dead8e6 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -1461,6 +1461,16 @@ enum nft_flowtable_hook_attributes {
 };
 #define NFTA_FLOWTABLE_HOOK_MAX	(__NFTA_FLOWTABLE_HOOK_MAX - 1)
 
+enum nft_osf_attributes {
+	NFTA_OSF_UNSPEC,
+	NFTA_OSF_DREG,
+	NFTA_OSF_FLAGS,
+	NFTA_OSF_LOGLEVEL,
+	NFTA_OSF_TTL,
+	__NFTA_OSF_MAX,
+};
+#define NFTA_OSF_MAX (__NFTA_OSF_MAX - 1)
+
 /**
  * enum nft_device_attributes - nf_tables device netlink attributes
  *
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 6c65d756e603..29c8591f87c2 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -633,6 +633,12 @@ config NFT_SOCKET
 	  This option allows matching for the presence or absence of a
 	  corresponding socket and its attributes.
 
+config NFT_OSF
+	tristate "Netfilter nf_tables passive OS fingerprinting support"
+	select NF_OSF
+	help
+	  This option allows matching packets from an specific OS.
+
 if NF_TABLES_NETDEV
 
 config NF_DUP_NETDEV
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 0b3851e825fa..75ddcb0f748d 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -109,6 +109,7 @@ obj-$(CONFIG_NFT_FIB_INET)	+= nft_fib_inet.o
 obj-$(CONFIG_NFT_FIB_NETDEV)	+= nft_fib_netdev.o
 obj-$(CONFIG_NF_OSF)		+= nf_osf.o
 obj-$(CONFIG_NFT_SOCKET)	+= nft_socket.o
+obj-$(CONFIG_NFT_OSF)		+= nft_osf.o
 
 # nf_tables netdev
 obj-$(CONFIG_NFT_DUP_NETDEV)	+= nft_dup_netdev.o
diff --git a/net/netfilter/nft_osf.c b/net/netfilter/nft_osf.c
new file mode 100644
index 000000000000..596f835087a6
--- /dev/null
+++ b/net/netfilter/nft_osf.c
@@ -0,0 +1,118 @@
+#include <net/netfilter/nf_tables.h>
+#include <linux/netfilter/nf_osf.h>
+
+#define OSF_GENRE_SIZE		32
+
+struct nft_osf {
+	__u8	flags;
+	__u8	loglevel;
+	__u8	ttl;
+	union {
+		enum nft_registers	dreg:8;
+	};
+};
+
+/* placeholder function WIP */
+static inline bool match_packet(struct nft_osf *priv, struct sk_buff *skb)
+{
+	return 1;
+}
+
+static const struct nla_policy nft_osf_policy[NFTA_OSF_MAX + 1] = {
+	[NFTA_OSF_DREG]		= { .type = NLA_U32 },
+	[NFTA_OSF_FLAGS]	= { .type = NLA_U8 },
+	[NFTA_OSF_LOGLEVEL]	= { .type = NLA_U8 },
+	[NFTA_OSF_TTL]		= { .type = NLA_U8 },
+};
+
+static void nft_osf_eval(const struct nft_expr *expr, struct nft_regs *regs,
+			 const struct nft_pktinfo *pkt)
+{
+	struct nft_osf *priv = nft_expr_priv(expr);
+	struct sk_buff *skb = pkt->skb;
+
+	if (!match_packet(priv, skb))
+		regs->verdict.code = NFT_BREAK;
+}
+
+static int nft_osf_init(const struct nft_ctx *ctx,
+			const struct nft_expr *expr,
+			const struct nlattr * const tb[])
+{
+	struct nft_osf *priv = nft_expr_priv(expr);
+	int err;
+	__u8 flags, loglevel, ttl;
+
+	priv->dreg = nft_parse_register(tb[NFTA_OSF_DREG]);
+	err = nft_validate_register_store(ctx, priv->dreg, NULL,
+					  NFTA_DATA_VALUE, OSF_GENRE_SIZE);
+	if (err < 0)
+		return err;
+
+	flags = ntohl(nla_get_be32(tb[NFTA_OSF_FLAGS]));
+	if (flags & ~NF_OSF_FLAGMASK)
+		return -EINVAL;
+	priv->flags	= flags;
+
+	loglevel = ntohl(nla_get_be32(tb[NFTA_OSF_LOGLEVEL]));
+	if (loglevel >= NF_OSF_LOGLEVEL_ALL_KNOWN)
+		return -EINVAL;
+	priv->loglevel	= loglevel;
+
+	ttl = ntohl(nla_get_be32(tb[NFTA_OSF_TTL]));
+	if (ttl >= NF_OSF_TTL_NOCHECK)
+		return -EINVAL;
+	priv->ttl	= ttl;
+
+	return 0;
+}
+
+static int nft_osf_dump(struct sk_buff *skb, const struct nft_expr *expr)
+{
+	const struct nft_osf *priv = nft_expr_priv(expr);
+
+	if (nft_dump_register(skb, NFTA_OSF_DREG, priv->dreg) ||
+	    nla_put_be32(skb, NFTA_OSF_FLAGS, htonl(priv->flags)) ||
+	    nla_put_be32(skb, NFTA_OSF_LOGLEVEL, htonl(priv->loglevel)) ||
+	    nla_put_be32(skb, NFTA_OSF_TTL, htonl(priv->ttl)))
+		goto nla_put_failure;
+	return 0;
+
+nla_put_failure:
+	return -1;
+}
+
+static struct nft_expr_type nft_osf_type;
+
+static const struct nft_expr_ops nft_osf_op = {
+	.eval = nft_osf_eval,
+	.size = NFT_EXPR_SIZE(sizeof(struct nft_osf)),
+	.init = nft_osf_init,
+	.dump = nft_osf_dump,
+	.type = &nft_osf_type,
+};
+
+static struct nft_expr_type nft_osf_type __read_mostly = {
+	.ops = &nft_osf_op,
+	.name = "osf",
+	.owner = THIS_MODULE,
+	.policy = nft_osf_policy,
+	.maxattr = NFTA_OSF_MAX,
+};
+
+static int __init nft_osf_module_init(void)
+{
+	return nft_register_expr(&nft_osf_type);
+}
+
+static void __exit nft_osf_module_exit(void)
+{
+	return nft_unregister_expr(&nft_osf_type);
+}
+
+module_init(nft_osf_module_init);
+module_exit(nft_osf_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Fernando Fernandez <ffmancera@xxxxxxxxxx>");
+MODULE_ALIAS_NFT_EXPR("osf");
-- 
2.18.0

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