netfilter: nf_osf: rename nf_osf.c to nfnetlink_osf.c

Rename nf_osf.c to nfnetlink_osf.c as we introduce nfnetlink_osf which is
the OSF infraestructure.

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

net/netfilter/Kconfig

@@ -46,6 +46,14 @@ config NETFILTER_NETLINK_LOG
 	  and is also scheduled to replace the old syslog-based ipt_LOG
 	  and ip6t_LOG modules.
 
+config NETFILTER_NETLINK_OSF
+	tristate "Netfilter OSF over NFNETLINK interface"
+	depends on NETFILTER_ADVANCED
+	select NETFILTER_NETLINK
+	help
+	  If this option is enabled, the kernel will include support
+	  for passive OS fingerprint via NFNETLINK.
+
 config NF_CONNTRACK
 	tristate "Netfilter connection tracking support"
 	default m if NETFILTER_ADVANCED=n
@@ -442,9 +450,6 @@ config NETFILTER_SYNPROXY
 
 endif # NF_CONNTRACK
 
-config NF_OSF
-	tristate
-
 config NF_TABLES
 	select NETFILTER_NETLINK
 	tristate "Netfilter nf_tables support"
@@ -1368,8 +1373,8 @@ 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
+	depends on NETFILTER_ADVANCED
+	select NETFILTER_NETLINK_OSF
 	help
 	  This option selects the Passive OS Fingerprinting match module
 	  that allows to passively match the remote operating system by

net/netfilter/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_NETFILTER_NETLINK) += nfnetlink.o
 obj-$(CONFIG_NETFILTER_NETLINK_ACCT) += nfnetlink_acct.o
 obj-$(CONFIG_NETFILTER_NETLINK_QUEUE) += nfnetlink_queue.o
 obj-$(CONFIG_NETFILTER_NETLINK_LOG) += nfnetlink_log.o
+obj-$(CONFIG_NETFILTER_NETLINK_OSF) += nfnetlink_osf.o
 
 # connection tracking
 obj-$(CONFIG_NF_CONNTRACK) += nf_conntrack.o
@@ -108,7 +109,6 @@ obj-$(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
 obj-$(CONFIG_NFT_SOCKET)	+= nft_socket.o
 
 # nf_tables netdev

net/netfilter/nfnetlink_osf.c

@@ -0,0 +1,282 @@
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+#include <linux/capability.h>
+#include <linux/if.h>
+#include <linux/inetdevice.h>
+#include <linux/ip.h>
+#include <linux/list.h>
+#include <linux/rculist.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/tcp.h>
+
+#include <net/ip.h>
+#include <net/tcp.h>
+
+#include <linux/netfilter/nfnetlink.h>
+#include <linux/netfilter/x_tables.h>
+#include <net/netfilter/nf_log.h>
+#include <linux/netfilter/nf_osf.h>
+
+static inline int nf_osf_ttl(const struct sk_buff *skb,
+			     int ttl_check, unsigned char f_ttl)
+{
+	const struct iphdr *ip = ip_hdr(skb);
+
+	if (ttl_check != -1) {
+		if (ttl_check == NF_OSF_TTL_TRUE)
+			return ip->ttl == f_ttl;
+		if (ttl_check == NF_OSF_TTL_NOCHECK)
+			return 1;
+		else if (ip->ttl <= f_ttl)
+			return 1;
+		else {
+			struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
+			int ret = 0;
+
+			for_ifa(in_dev) {
+				if (inet_ifa_match(ip->saddr, ifa)) {
+					ret = (ip->ttl == f_ttl);
+					break;
+				}
+			}
+			endfor_ifa(in_dev);
+
+			return ret;
+		}
+	}
+
+	return ip->ttl == f_ttl;
+}
+
+struct nf_osf_hdr_ctx {
+	bool			df;
+	u16			window;
+	u16			totlen;
+	const unsigned char	*optp;
+	unsigned int		optsize;
+};
+
+static bool nf_osf_match_one(const struct sk_buff *skb,
+			     const struct nf_osf_user_finger *f,
+			     int ttl_check,
+			     struct nf_osf_hdr_ctx *ctx)
+{
+	unsigned int check_WSS = 0;
+	int fmatch = FMATCH_WRONG;
+	int foptsize, optnum;
+	u16 mss = 0;
+
+	if (ctx->totlen != f->ss || !nf_osf_ttl(skb, ttl_check, f->ttl))
+		return false;
+
+	/*
+	 * Should not happen if userspace parser was written correctly.
+	 */
+	if (f->wss.wc >= OSF_WSS_MAX)
+		return false;
+
+	/* Check options */
+
+	foptsize = 0;
+	for (optnum = 0; optnum < f->opt_num; ++optnum)
+		foptsize += f->opt[optnum].length;
+
+	if (foptsize > MAX_IPOPTLEN ||
+	    ctx->optsize > MAX_IPOPTLEN ||
+	    ctx->optsize != foptsize)
+		return false;
+
+	check_WSS = f->wss.wc;
+
+	for (optnum = 0; optnum < f->opt_num; ++optnum) {
+		if (f->opt[optnum].kind == *ctx->optp) {
+			__u32 len = f->opt[optnum].length;
+			const __u8 *optend = ctx->optp + len;
+
+			fmatch = FMATCH_OK;
+
+			switch (*ctx->optp) {
+			case OSFOPT_MSS:
+				mss = ctx->optp[3];
+				mss <<= 8;
+				mss |= ctx->optp[2];
+
+				mss = ntohs((__force __be16)mss);
+				break;
+			case OSFOPT_TS:
+				break;
+			}
+
+			ctx->optp = optend;
+		} else
+			fmatch = FMATCH_OPT_WRONG;
+
+		if (fmatch != FMATCH_OK)
+			break;
+	}
+
+	if (fmatch != FMATCH_OPT_WRONG) {
+		fmatch = FMATCH_WRONG;
+
+		switch (check_WSS) {
+		case OSF_WSS_PLAIN:
+			if (f->wss.val == 0 || ctx->window == f->wss.val)
+				fmatch = FMATCH_OK;
+			break;
+		case OSF_WSS_MSS:
+			/*
+			 * Some smart modems decrease mangle MSS to
+			 * SMART_MSS_2, so we check standard, decreased
+			 * and the one provided in the fingerprint MSS
+			 * values.
+			 */
+#define SMART_MSS_1	1460
+#define SMART_MSS_2	1448
+			if (ctx->window == f->wss.val * mss ||
+			    ctx->window == f->wss.val * SMART_MSS_1 ||
+			    ctx->window == f->wss.val * SMART_MSS_2)
+				fmatch = FMATCH_OK;
+			break;
+		case OSF_WSS_MTU:
+			if (ctx->window == f->wss.val * (mss + 40) ||
+			    ctx->window == f->wss.val * (SMART_MSS_1 + 40) ||
+			    ctx->window == f->wss.val * (SMART_MSS_2 + 40))
+				fmatch = FMATCH_OK;
+			break;
+		case OSF_WSS_MODULO:
+			if ((ctx->window % f->wss.val) == 0)
+				fmatch = FMATCH_OK;
+			break;
+		}
+	}
+
+	return fmatch == FMATCH_OK;
+}
+
+static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
+						const struct sk_buff *skb,
+						const struct iphdr *ip,
+						unsigned char *opts)
+{
+	const struct tcphdr *tcp;
+	struct tcphdr _tcph;
+
+	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
+	if (!tcp)
+		return NULL;
+
+	if (!tcp->syn)
+		return NULL;
+
+	ctx->totlen = ntohs(ip->tot_len);
+	ctx->df = ntohs(ip->frag_off) & IP_DF;
+	ctx->window = ntohs(tcp->window);
+
+	if (tcp->doff * 4 > sizeof(struct tcphdr)) {
+		ctx->optsize = tcp->doff * 4 - sizeof(struct tcphdr);
+
+		ctx->optp = skb_header_pointer(skb, ip_hdrlen(skb) +
+				sizeof(struct tcphdr), ctx->optsize, opts);
+	}
+
+	return tcp;
+}
+
+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)
+{
+	const struct iphdr *ip = ip_hdr(skb);
+	const struct nf_osf_user_finger *f;
+	unsigned char opts[MAX_IPOPTLEN];
+	const struct nf_osf_finger *kf;
+	int fcount = 0, ttl_check;
+	int fmatch = FMATCH_WRONG;
+	struct nf_osf_hdr_ctx ctx;
+	const struct tcphdr *tcp;
+
+	memset(&ctx, 0, sizeof(ctx));
+
+	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
+	if (!tcp)
+		return false;
+
+	ttl_check = (info->flags & NF_OSF_TTL) ? info->ttl : -1;
+
+	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
+
+		f = &kf->finger;
+
+		if (!(info->flags & NF_OSF_LOG) && strcmp(info->genre, f->genre))
+			continue;
+
+		if (!nf_osf_match_one(skb, f, ttl_check, &ctx))
+			continue;
+
+		fmatch = FMATCH_OK;
+
+		fcount++;
+
+		if (info->flags & NF_OSF_LOG)
+			nf_log_packet(net, family, hooknum, skb,
+				      in, out, NULL,
+				      "%s [%s:%s] : %pI4:%d -> %pI4:%d hops=%d\n",
+				      f->genre, f->version, f->subtype,
+				      &ip->saddr, ntohs(tcp->source),
+				      &ip->daddr, ntohs(tcp->dest),
+				      f->ttl - ip->ttl);
+
+		if ((info->flags & NF_OSF_LOG) &&
+		    info->loglevel == NF_OSF_LOGLEVEL_FIRST)
+			break;
+	}
+
+	if (!fcount && (info->flags & NF_OSF_LOG))
+		nf_log_packet(net, family, hooknum, skb, in, out, NULL,
+			      "Remote OS is not known: %pI4:%u -> %pI4:%u\n",
+			      &ip->saddr, ntohs(tcp->source),
+			      &ip->daddr, ntohs(tcp->dest));
+
+	if (fcount)
+		fmatch = FMATCH_OK;
+
+	return fmatch == FMATCH_OK;
+}
+EXPORT_SYMBOL_GPL(nf_osf_match);
+
+const char *nf_osf_find(const struct sk_buff *skb,
+			const struct list_head *nf_osf_fingers)
+{
+	const struct iphdr *ip = ip_hdr(skb);
+	const struct nf_osf_user_finger *f;
+	unsigned char opts[MAX_IPOPTLEN];
+	const struct nf_osf_finger *kf;
+	struct nf_osf_hdr_ctx ctx;
+	const struct tcphdr *tcp;
+	const char *genre = NULL;
+
+	memset(&ctx, 0, sizeof(ctx));
+
+	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
+	if (!tcp)
+		return false;
+
+	list_for_each_entry_rcu(kf, &nf_osf_fingers[ctx.df], finger_entry) {
+		f = &kf->finger;
+		if (!nf_osf_match_one(skb, f, -1, &ctx))
+			continue;
+
+		genre = f->genre;
+		break;
+	}
+
+	return genre;
+}
+EXPORT_SYMBOL_GPL(nf_osf_find);
+
+MODULE_LICENSE("GPL");