[PATCH] SANE conntrack helper

[Michal Schmidt <xschmi00@stud.feec.vutbr.cz>]

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Hi,

This is nf_conntrack_sane, a netfilter connection tracking helper
module for the SANE protocol used by the 'saned' daemon to make scanners
available via network.
The SANE protocol uses separate control & data connections, similar to
passive FTP. The helper module is needed to recognize the data
connection as RELATED to the control one.

Patrick, this version is ported to the current nf_conntrack changes and 
I've made the cleanups and fixes you recommended last week.

Signed-off-by: Michal Schmidt <xschmi00@stud.feec.vutbr.cz>

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diff --git a/include/linux/netfilter/nf_conntrack_sane.h b/include/linux/netfilter/nf_conntrack_sane.h
new file mode 100644
index 0000000..4767d6e
--- /dev/null
+++ b/include/linux/netfilter/nf_conntrack_sane.h
@@ -0,0 +1,21 @@
+#ifndef _NF_CONNTRACK_SANE_H
+#define _NF_CONNTRACK_SANE_H
+/* SANE tracking. */
+
+#ifdef __KERNEL__
+
+#define SANE_PORT	6566
+
+enum sane_state {
+	SANE_STATE_NORMAL,
+	SANE_STATE_START_REQUESTED,
+};
+
+/* This structure exists only once per master */
+struct nf_ct_sane_master {
+	enum sane_state state;
+};
+
+#endif /* __KERNEL__ */
+
+#endif /* _NF_CONNTRACK_SANE_H */
diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index 032b36a..659387e 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -45,6 +45,7 @@ union nf_conntrack_expect_proto {
 #include <linux/netfilter/nf_conntrack_ftp.h>
 #include <linux/netfilter/nf_conntrack_pptp.h>
 #include <linux/netfilter/nf_conntrack_h323.h>
+#include <linux/netfilter/nf_conntrack_sane.h>
 
 /* per conntrack: application helper private data */
 union nf_conntrack_help {
@@ -52,6 +53,7 @@ union nf_conntrack_help {
 	struct nf_ct_ftp_master ct_ftp_info;
 	struct nf_ct_pptp_master ct_pptp_info;
 	struct nf_ct_h323_master ct_h323_info;
+	struct nf_ct_sane_master ct_sane_info;
 };
 
 #include <linux/types.h>
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index 3a66878..8dfac50 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -236,6 +236,19 @@ config NF_CONNTRACK_PPTP
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+config NF_CONNTRACK_SANE
+	tristate "SANE protocol support (EXPERIMENTAL)"
+	depends on EXPERIMENTAL && NF_CONNTRACK
+	help
+	  SANE is a protocol for remote access to scanners as implemented
+	  by the 'saned' daemon. Like FTP, it uses separate control and
+	  data connections.
+
+	  With this module you can support SANE on a connection tracking
+	  firewall.
+
+	  To compile it as a module, choose M here.  If unsure, say N.
+
 config NF_CONNTRACK_SIP
 	tristate "SIP protocol support (EXPERIMENTAL)"
 	depends on EXPERIMENTAL && NF_CONNTRACK
diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 5dc5574..5054b0f 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -29,6 +29,7 @@ obj-$(CONFIG_NF_CONNTRACK_H323) += nf_conntrack_h323.o
 obj-$(CONFIG_NF_CONNTRACK_IRC) += nf_conntrack_irc.o
 obj-$(CONFIG_NF_CONNTRACK_NETBIOS_NS) += nf_conntrack_netbios_ns.o
 obj-$(CONFIG_NF_CONNTRACK_PPTP) += nf_conntrack_pptp.o
+obj-$(CONFIG_NF_CONNTRACK_SANE) += nf_conntrack_sane.o
 obj-$(CONFIG_NF_CONNTRACK_SIP) += nf_conntrack_sip.o
 obj-$(CONFIG_NF_CONNTRACK_TFTP) += nf_conntrack_tftp.o
 
diff --git a/net/netfilter/nf_conntrack_sane.c b/net/netfilter/nf_conntrack_sane.c
new file mode 100644
index 0000000..6b96f93
--- /dev/null
+++ b/net/netfilter/nf_conntrack_sane.c
@@ -0,0 +1,236 @@
+/* SANE connection tracking helper
+ * (SANE = Scanner Access Now Easy)
+ * For documentation about the SANE network protocol see
+ * http://www.sane-project.org/html/doc015.html
+ */
+
+/* (C) 2006 Michal Schmidt
+ * Based on the FTP conntrack helper (net/netfilter/nf_conntrack_ftp.c)
+ * (C) 1999-2001 Paul `Rusty' Russell
+ * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
+ * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
+ * (C) 2003 Yasuyuki Kozakai @USAGI <yasuyuki.kozakai@toshiba.co.jp>
+ *
+ * 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/module.h>
+#include <linux/moduleparam.h>
+#include <linux/netfilter.h>
+#include <linux/in.h>
+#include <linux/tcp.h>
+#include <net/netfilter/nf_conntrack.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <linux/netfilter/nf_conntrack_sane.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michal Schmidt <xschmi00@stud.feec.vutbr.cz>");
+MODULE_DESCRIPTION("SANE connection tracking helper");
+
+static char *sane_buffer;
+
+static DEFINE_SPINLOCK(nf_sane_lock);
+
+#define MAX_PORTS 8
+static u_int16_t ports[MAX_PORTS];
+static unsigned int ports_c;
+module_param_array(ports, ushort, &ports_c, 0400);
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+struct sane_request {
+	__be32 RPC_code;
+};
+#define SANE_NET_START      7   /* RPC code */
+
+struct sane_reply_net_start {
+	__be32 status;
+
+	__be16 zero;
+	__be16 port;
+	/* other fields aren't interesting for conntrack */
+};
+#define SANE_STATUS_SUCCESS 0
+
+static int help(struct sk_buff **pskb,
+		unsigned int protoff,
+		struct nf_conn *ct,
+		enum ip_conntrack_info ctinfo)
+{
+	unsigned int dataoff, datalen;
+	struct tcphdr _tcph, *th;
+	char *sb_ptr;
+	int ret = NF_ACCEPT;
+	int dir = CTINFO2DIR(ctinfo);
+	struct nf_ct_sane_master *ct_sane_info = &nfct_help(ct)->help.ct_sane_info;
+	struct nf_conntrack_expect *exp;
+	struct nf_conntrack_tuple *tuple;
+	struct sane_request *req;
+	struct sane_reply_net_start *reply;
+	int family = ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.l3num;
+
+	/* Until there's been traffic both ways, don't look in packets. */
+	if (ctinfo != IP_CT_ESTABLISHED
+	    && ctinfo != IP_CT_ESTABLISHED+IP_CT_IS_REPLY)
+		return NF_ACCEPT;
+
+	/* Not a full tcp header? */
+	th = skb_header_pointer(*pskb, protoff, sizeof(_tcph), &_tcph);
+	if (th == NULL)
+		return NF_ACCEPT;
+
+	/* No data? */
+	dataoff = protoff + th->doff * 4;
+	if (dataoff >= (*pskb)->len)
+		return NF_ACCEPT;
+
+	datalen = (*pskb)->len - dataoff;
+
+	spin_lock_bh(&nf_sane_lock);
+	sb_ptr = skb_header_pointer(*pskb, dataoff, datalen, sane_buffer);
+	BUG_ON(sb_ptr == NULL);
+
+	if (dir == IP_CT_DIR_ORIGINAL) {
+		if (datalen < sizeof(struct sane_request))
+			goto out;
+
+		req = (struct sane_request*) sb_ptr;
+		if (req->RPC_code != htonl(SANE_NET_START)) {
+			/* Not an interesting command */
+			ct_sane_info->state = SANE_STATE_NORMAL;
+			goto out;
+		}
+
+		/* We're interested in the next reply */
+		ct_sane_info->state = SANE_STATE_START_REQUESTED;
+		goto out;
+	}
+
+	/* Is it a reply to an uninteresting command? */
+	if (ct_sane_info->state != SANE_STATE_START_REQUESTED)
+		goto out;
+
+	/* It's a reply to SANE_NET_START */
+	if (datalen < sizeof(struct sane_reply_net_start))
+		goto out;
+
+	/* OK, we're picking it up. Reset the state. */
+	ct_sane_info->state = SANE_STATE_NORMAL;
+
+	reply = (struct sane_reply_net_start*) sb_ptr;
+	if (reply->status != htonl(SANE_STATUS_SUCCESS)) {
+		/* saned refused the command */
+		DEBUGP("nf_ct_sane: unsuccessful SANE_STATUS = %u\n",
+			ntohl(reply->status));
+		goto out;
+	}
+
+	/* Invalid saned reply? Ignore it. */
+	if (reply->zero != 0)
+		goto out;
+
+	exp = nf_conntrack_expect_alloc(ct);
+	if (exp == NULL) {
+		ret = NF_DROP;
+		goto out;
+	}
+
+	tuple = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
+	nf_conntrack_expect_init(exp, family,
+				 &tuple->src.u3, &tuple->dst.u3,
+				 IPPROTO_TCP,
+				 NULL, &reply->port);
+
+	DEBUGP("nf_ct_sane: expect: ");
+	NF_CT_DUMP_TUPLE(&exp->tuple);
+	NF_CT_DUMP_TUPLE(&exp->mask);
+
+	/* Can't expect this?  Best to drop packet now. */
+	if (nf_conntrack_expect_related(exp) != 0)
+		ret = NF_DROP;
+
+	nf_conntrack_expect_put(exp);
+
+out:
+	spin_unlock_bh(&nf_sane_lock);
+	return ret;
+}
+
+static struct nf_conntrack_helper sane[MAX_PORTS][2];
+static char sane_names[MAX_PORTS][2][sizeof("sane-65535")];
+
+/* don't make this __exit, since it's called from __init ! */
+static void nf_conntrack_sane_fini(void)
+{
+	int i, j;
+	for (i = 0; i < ports_c; i++) {
+		for (j = 0; j < 2; j++) {
+			DEBUGP("nf_ct_sane: unregistering helper for pf: %d "
+			       "port: %d\n",
+				sane[i][j].tuple.src.l3num, ports[i]);
+			nf_conntrack_helper_unregister(&sane[i][j]);
+		}
+	}
+
+	kfree(sane_buffer);
+}
+
+static int __init nf_conntrack_sane_init(void)
+{
+	int i, j = -1, ret = 0;
+	char *tmpname;
+
+	sane_buffer = kmalloc(65536, GFP_KERNEL);
+	if (!sane_buffer)
+		return -ENOMEM;
+
+	if (ports_c == 0)
+		ports[ports_c++] = SANE_PORT;
+
+	/* FIXME should be configurable whether IPv4 and IPv6 connections
+		 are tracked or not - YK */
+	for (i = 0; i < ports_c; i++) {
+		sane[i][0].tuple.src.l3num = PF_INET;
+		sane[i][1].tuple.src.l3num = PF_INET6;
+		for (j = 0; j < 2; j++) {
+			sane[i][j].tuple.src.u.tcp.port = htons(ports[i]);
+			sane[i][j].tuple.dst.protonum = IPPROTO_TCP;
+			sane[i][j].mask.src.u.tcp.port = 0xFFFF;
+			sane[i][j].mask.dst.protonum = 0xFF;
+			sane[i][j].max_expected = 1;
+			sane[i][j].timeout = 5 * 60;	/* 5 Minutes */
+			sane[i][j].me = THIS_MODULE;
+			sane[i][j].help = help;
+			tmpname = &sane_names[i][j][0];
+			if (ports[i] == SANE_PORT)
+				sprintf(tmpname, "sane");
+			else
+				sprintf(tmpname, "sane-%d", ports[i]);
+			sane[i][j].name = tmpname;
+
+			DEBUGP("nf_ct_sane: registering helper for pf: %d "
+			       "port: %d\n",
+				sane[i][j].tuple.src.l3num, ports[i]);
+			ret = nf_conntrack_helper_register(&sane[i][j]);
+			if (ret) {
+				printk(KERN_ERR "nf_ct_sane: failed to "
+				       "register helper for pf: %d port: %d\n",
+					sane[i][j].tuple.src.l3num, ports[i]);
+				nf_conntrack_sane_fini();
+				return ret;
+			}
+		}
+	}
+
+	return 0;
+}
+
+module_init(nf_conntrack_sane_init);
+module_exit(nf_conntrack_sane_fini);