netfilter: extract Passive OS fingerprint infrastructure from xt_osf

Add nf_osf_ttl() and nf_osf_match() into nf_osf.c to prepare for
nf_tables support.

Signed-off-by: Fernando Fernandez Mancera <ffmancera@riseup.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter/nf_osf.h

@@ -0,0 +1,27 @@
+#include <uapi/linux/netfilter/nf_osf.h>
+
+/* Initial window size option state machine: multiple of mss, mtu or
+ * plain numeric value. Can also be made as plain numeric value which
+ * is not a multiple of specified value.
+ */
+enum nf_osf_window_size_options {
+	OSF_WSS_PLAIN   = 0,
+	OSF_WSS_MSS,
+	OSF_WSS_MTU,
+	OSF_WSS_MODULO,
+	OSF_WSS_MAX,
+};
+
+enum osf_fmatch_states {
+	/* Packet does not match the fingerprint */
+	FMATCH_WRONG = 0,
+	/* Packet matches the fingerprint */
+	FMATCH_OK,
+	/* Options do not match the fingerprint, but header does */
+	FMATCH_OPT_WRONG,
+};
+
+bool nf_osf_match(const struct sk_buff *skb, u_int8_t family,
+		  int hooknum, struct net_device *in, struct net_device *out,
+		  const struct nf_osf_info *info, struct net *net,
+		  const struct list_head *nf_osf_fingers);

include/uapi/linux/netfilter/nf_osf.h

@@ -0,0 +1,90 @@
+#ifndef _NF_OSF_H
+#define _NF_OSF_H
+
+#define MAXGENRELEN	32
+
+#define NF_OSF_GENRE	(1 << 0)
+#define NF_OSF_TTL	(1 << 1)
+#define NF_OSF_LOG	(1 << 2)
+#define NF_OSF_INVERT	(1 << 3)
+
+#define NF_OSF_LOGLEVEL_ALL		0	/* log all matched fingerprints */
+#define NF_OSF_LOGLEVEL_FIRST		1	/* log only the first matced fingerprint */
+#define NF_OSF_LOGLEVEL_ALL_KNOWN	2	/* do not log unknown packets */
+
+#define NF_OSF_TTL_TRUE			0	/* True ip and fingerprint TTL comparison */
+
+/* Do not compare ip and fingerprint TTL at all */
+#define NF_OSF_TTL_NOCHECK		2
+
+/* Wildcard MSS (kind of).
+ * It is used to implement a state machine for the different wildcard values
+ * of the MSS and window sizes.
+ */
+struct nf_osf_wc {
+	__u32	wc;
+	__u32	val;
+};
+
+/* This struct represents IANA options
+ * http://www.iana.org/assignments/tcp-parameters
+ */
+struct nf_osf_opt {
+	__u16			kind, length;
+	struct nf_osf_wc	wc;
+};
+
+struct nf_osf_info {
+	char	genre[MAXGENRELEN];
+	__u32	len;
+	__u32	flags;
+	__u32	loglevel;
+	__u32	ttl;
+};
+
+struct nf_osf_user_finger {
+	struct nf_osf_wc	wss;
+
+	__u8	ttl, df;
+	__u16	ss, mss;
+	__u16	opt_num;
+
+	char	genre[MAXGENRELEN];
+	char	version[MAXGENRELEN];
+	char	subtype[MAXGENRELEN];
+
+	/* MAX_IPOPTLEN is maximum if all options are NOPs or EOLs */
+	struct nf_osf_opt	opt[MAX_IPOPTLEN];
+};
+
+struct nf_osf_finger {
+	struct rcu_head			rcu_head;
+	struct list_head		finger_entry;
+	struct nf_osf_user_finger	finger;
+};
+
+struct nf_osf_nlmsg {
+	struct nf_osf_user_finger	f;
+	struct iphdr			ip;
+	struct tcphdr			tcp;
+};
+
+/* Defines for IANA option kinds */
+enum iana_options {
+	OSFOPT_EOL = 0,		/* End of options */
+	OSFOPT_NOP,		/* NOP */
+	OSFOPT_MSS,		/* Maximum segment size */
+	OSFOPT_WSO,		/* Window scale option */
+	OSFOPT_SACKP,		/* SACK permitted */
+	OSFOPT_SACK,		/* SACK */
+	OSFOPT_ECHO,
+	OSFOPT_ECHOREPLY,
+	OSFOPT_TS,		/* Timestamp option */
+	OSFOPT_POCP,		/* Partial Order Connection Permitted */
+	OSFOPT_POSP,		/* Partial Order Service Profile */
+
+	/* Others are not used in the current OSF */
+	OSFOPT_EMPTY = 255,
+};
+
+#endif /* _NF_OSF_H */

include/uapi/linux/netfilter/xt_osf.h

@@ -23,101 +23,29 @@
 #include <linux/types.h>
 #include <linux/ip.h>
 #include <linux/tcp.h>
+#include <linux/netfilter/nf_osf.h>
 
-#define MAXGENRELEN		32
+#define XT_OSF_GENRE		NF_OSF_GENRE
+#define XT_OSF_INVERT		NF_OSF_INVERT
 
-#define XT_OSF_GENRE		(1<<0)
-#define	XT_OSF_TTL		(1<<1)
-#define XT_OSF_LOG		(1<<2)
-#define XT_OSF_INVERT		(1<<3)
+#define XT_OSF_TTL		NF_OSF_TTL
+#define XT_OSF_LOG		NF_OSF_LOG
 
-#define XT_OSF_LOGLEVEL_ALL	0	/* log all matched fingerprints */
-#define XT_OSF_LOGLEVEL_FIRST	1	/* log only the first matced fingerprint */
-#define XT_OSF_LOGLEVEL_ALL_KNOWN	2 /* do not log unknown packets */
+#define XT_OSF_LOGLEVEL_ALL		NF_OSF_LOGLEVEL_ALL
+#define XT_OSF_LOGLEVEL_FIRST		NF_OSF_LOGLEVEL_FIRST
+#define XT_OSF_LOGLEVEL_ALL_KNOWN	NF_OSF_LOGLEVEL_ALL_KNOWN
 
-#define XT_OSF_TTL_TRUE		0	/* True ip and fingerprint TTL comparison */
-#define XT_OSF_TTL_LESS		1	/* Check if ip TTL is less than fingerprint one */
-#define XT_OSF_TTL_NOCHECK	2	/* Do not compare ip and fingerprint TTL at all */
+#define XT_OSF_TTL_TRUE		NF_OSF_TTL_TRUE
+#define XT_OSF_TTL_NOCHECK	NF_OSF_TTL_NOCHECK
 
-struct xt_osf_info {
-	char			genre[MAXGENRELEN];
-	__u32			len;
-	__u32			flags;
-	__u32			loglevel;
-	__u32			ttl;
-};
-
-/*
- * Wildcard MSS (kind of).
- * It is used to implement a state machine for the different wildcard values
- * of the MSS and window sizes.
- */
-struct xt_osf_wc {
-	__u32			wc;
-	__u32			val;
-};
-
-/*
- * This struct represents IANA options
- * http://www.iana.org/assignments/tcp-parameters
- */
-struct xt_osf_opt {
-	__u16			kind, length;
-	struct xt_osf_wc	wc;
-};
-
-struct xt_osf_user_finger {
-	struct xt_osf_wc	wss;
-
-	__u8			ttl, df;
-	__u16			ss, mss;
-	__u16			opt_num;
-
-	char			genre[MAXGENRELEN];
-	char			version[MAXGENRELEN];
-	char			subtype[MAXGENRELEN];
+#define XT_OSF_TTL_LESS	1	/* Check if ip TTL is less than fingerprint one */
 
-	/* MAX_IPOPTLEN is maximum if all options are NOPs or EOLs */
-	struct xt_osf_opt	opt[MAX_IPOPTLEN];
-};
-
-struct xt_osf_nlmsg {
-	struct xt_osf_user_finger	f;
-	struct iphdr		ip;
-	struct tcphdr		tcp;
-};
-
-/* Defines for IANA option kinds */
-
-enum iana_options {
-	OSFOPT_EOL = 0,		/* End of options */
-	OSFOPT_NOP, 		/* NOP */
-	OSFOPT_MSS, 		/* Maximum segment size */
-	OSFOPT_WSO, 		/* Window scale option */
-	OSFOPT_SACKP,		/* SACK permitted */
-	OSFOPT_SACK,		/* SACK */
-	OSFOPT_ECHO,
-	OSFOPT_ECHOREPLY,
-	OSFOPT_TS,		/* Timestamp option */
-	OSFOPT_POCP,		/* Partial Order Connection Permitted */
-	OSFOPT_POSP,		/* Partial Order Service Profile */
-
-	/* Others are not used in the current OSF */
-	OSFOPT_EMPTY = 255,
-};
-
-/*
- * Initial window size option state machine: multiple of mss, mtu or
- * plain numeric value. Can also be made as plain numeric value which
- * is not a multiple of specified value.
- */
-enum xt_osf_window_size_options {
-	OSF_WSS_PLAIN	= 0,
-	OSF_WSS_MSS,
-	OSF_WSS_MTU,
-	OSF_WSS_MODULO,
-	OSF_WSS_MAX,
-};
+#define xt_osf_wc		nf_osf_wc
+#define xt_osf_opt		nf_osf_opt
+#define xt_osf_info		nf_osf_info
+#define xt_osf_user_finger	nf_osf_user_finger
+#define xt_osf_finger		nf_osf_finger
+#define xt_osf_nlmsg		nf_osf_nlmsg
 
 /*
  * Add/remove fingerprint from the kernel.

net/netfilter/Kconfig

@@ -444,6 +444,9 @@ config NETFILTER_SYNPROXY
 
 endif # NF_CONNTRACK
 
+config NF_OSF
+	tristate 'Passive OS fingerprint infrastructure'
+
 config NF_TABLES
 	select NETFILTER_NETLINK
 	tristate "Netfilter nf_tables support"
@@ -1358,6 +1361,7 @@ config NETFILTER_XT_MATCH_NFACCT
 config NETFILTER_XT_MATCH_OSF
 	tristate '"osf" Passive OS fingerprint match'
 	depends on NETFILTER_ADVANCED && NETFILTER_NETLINK
+	select NF_OSF
 	help
 	  This option selects the Passive OS Fingerprinting match module
 	  that allows to passively match the remote operating system by

net/netfilter/Makefile

@@ -101,6 +101,7 @@ obj-$(CONFIG_NFT_HASH)		+= nft_hash.o
 obj-$(CONFIG_NFT_FIB)		+= nft_fib.o
 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
 
 # nf_tables netdev
 obj-$(CONFIG_NFT_DUP_NETDEV)	+= nft_dup_netdev.o