[NETFILTER]: nf_nat: add FTP NAT helper port

Add FTP NAT helper.

Split out from Jozsef's big nf_nat patch with a few small fixes by myself.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 200 insertions, 9 deletions

diff --git a/net/ipv4/netfilter/Kconfig b/net/ipv4/netfilter/Kconfig
index 01789ae..52f876d 100644
--- a/net/ipv4/netfilter/Kconfig
+++ b/net/ipv4/netfilter/Kconfig
@@ -477,20 +477,29 @@ config IP_NF_NAT_SNMP_BASIC
 
 	  To compile it as a module, choose M here.  If unsure, say N.
 
+# If they want FTP, set to $CONFIG_IP_NF_NAT (m or y),
+# or $CONFIG_IP_NF_FTP (m or y), whichever is weaker.
+# From kconfig-language.txt:
+#
+#           <expr> '&&' <expr>                   (6)
+#
+# (6) Returns the result of min(/expr/, /expr/).
+config IP_NF_NAT_FTP
+	tristate
+	depends on IP_NF_IPTABLES && IP_NF_CONNTRACK && IP_NF_NAT
+	default IP_NF_NAT && IP_NF_FTP
+
+config NF_NAT_FTP
+	tristate
+	depends on IP_NF_IPTABLES && NF_CONNTRACK && NF_NAT
+	default NF_NAT && NF_CONNTRACK_FTP
+
 config IP_NF_NAT_IRC
 	tristate
 	depends on IP_NF_IPTABLES!=n && IP_NF_CONNTRACK!=n && IP_NF_NAT!=n
 	default IP_NF_NAT if IP_NF_IRC=y
 	default m if IP_NF_IRC=m
 
-# If they want FTP, set to $CONFIG_IP_NF_NAT (m or y), 
-# or $CONFIG_IP_NF_FTP (m or y), whichever is weaker.  Argh.
-config IP_NF_NAT_FTP
-	tristate
-	depends on IP_NF_IPTABLES!=n && IP_NF_CONNTRACK!=n && IP_NF_NAT!=n
-	default IP_NF_NAT if IP_NF_FTP=y
-	default m if IP_NF_FTP=m
-
 config IP_NF_NAT_TFTP
 	tristate
 	depends on IP_NF_IPTABLES!=n && IP_NF_CONNTRACK!=n && IP_NF_NAT!=n
diff --git a/net/ipv4/netfilter/Makefile b/net/ipv4/netfilter/Makefile
index ec31690..c0c6194 100644
--- a/net/ipv4/netfilter/Makefile
+++ b/net/ipv4/netfilter/Makefile
@@ -40,7 +40,7 @@ obj-$(CONFIG_IP_NF_IRC) += ip_conntrack_irc.o
 obj-$(CONFIG_IP_NF_SIP) += ip_conntrack_sip.o
 obj-$(CONFIG_IP_NF_NETBIOS_NS) += ip_conntrack_netbios_ns.o
 
-# NAT helpers 
+# NAT helpers (ip_conntrack)
 obj-$(CONFIG_IP_NF_NAT_H323) += ip_nat_h323.o
 obj-$(CONFIG_IP_NF_NAT_PPTP) += ip_nat_pptp.o
 obj-$(CONFIG_IP_NF_NAT_AMANDA) += ip_nat_amanda.o
@@ -49,6 +49,9 @@ obj-$(CONFIG_IP_NF_NAT_FTP) += ip_nat_ftp.o
 obj-$(CONFIG_IP_NF_NAT_IRC) += ip_nat_irc.o
 obj-$(CONFIG_IP_NF_NAT_SIP) += ip_nat_sip.o
 
+# NAT helpers (nf_conntrack)
+obj-$(CONFIG_NF_NAT_FTP) += nf_nat_ftp.o
+
 # generic IP tables 
 obj-$(CONFIG_IP_NF_IPTABLES) += ip_tables.o
 
diff --git a/net/ipv4/netfilter/nf_nat_ftp.c b/net/ipv4/netfilter/nf_nat_ftp.c
new file mode 100644
index 0000000..751b598
--- /dev/null
+++ b/net/ipv4/netfilter/nf_nat_ftp.c
@@ -0,0 +1,179 @@
+/* FTP extension for TCP NAT alteration. */
+
+/* (C) 1999-2001 Paul `Rusty' Russell
+ * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
+ *
+ * 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/ip.h>
+#include <linux/tcp.h>
+#include <linux/netfilter_ipv4.h>
+#include <net/netfilter/nf_nat.h>
+#include <net/netfilter/nf_nat_helper.h>
+#include <net/netfilter/nf_nat_rule.h>
+#include <net/netfilter/nf_conntrack_helper.h>
+#include <net/netfilter/nf_conntrack_expect.h>
+#include <linux/netfilter/nf_conntrack_ftp.h>
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
+MODULE_DESCRIPTION("ftp NAT helper");
+MODULE_ALIAS("ip_nat_ftp");
+
+#if 0
+#define DEBUGP printk
+#else
+#define DEBUGP(format, args...)
+#endif
+
+/* FIXME: Time out? --RR */
+
+static int
+mangle_rfc959_packet(struct sk_buff **pskb,
+		     __be32 newip,
+		     u_int16_t port,
+		     unsigned int matchoff,
+		     unsigned int matchlen,
+		     struct nf_conn *ct,
+		     enum ip_conntrack_info ctinfo,
+		     u32 *seq)
+{
+	char buffer[sizeof("nnn,nnn,nnn,nnn,nnn,nnn")];
+
+	sprintf(buffer, "%u,%u,%u,%u,%u,%u",
+		NIPQUAD(newip), port>>8, port&0xFF);
+
+	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
+
+	*seq += strlen(buffer) - matchlen;
+	return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
+					matchlen, buffer, strlen(buffer));
+}
+
+/* |1|132.235.1.2|6275| */
+static int
+mangle_eprt_packet(struct sk_buff **pskb,
+		   __be32 newip,
+		   u_int16_t port,
+		   unsigned int matchoff,
+		   unsigned int matchlen,
+		   struct nf_conn *ct,
+		   enum ip_conntrack_info ctinfo,
+		   u32 *seq)
+{
+	char buffer[sizeof("|1|255.255.255.255|65535|")];
+
+	sprintf(buffer, "|1|%u.%u.%u.%u|%u|", NIPQUAD(newip), port);
+
+	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
+
+	*seq += strlen(buffer) - matchlen;
+	return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
+					matchlen, buffer, strlen(buffer));
+}
+
+/* |1|132.235.1.2|6275| */
+static int
+mangle_epsv_packet(struct sk_buff **pskb,
+		   __be32 newip,
+		   u_int16_t port,
+		   unsigned int matchoff,
+		   unsigned int matchlen,
+		   struct nf_conn *ct,
+		   enum ip_conntrack_info ctinfo,
+		   u32 *seq)
+{
+	char buffer[sizeof("|||65535|")];
+
+	sprintf(buffer, "|||%u|", port);
+
+	DEBUGP("calling nf_nat_mangle_tcp_packet\n");
+
+	*seq += strlen(buffer) - matchlen;
+	return nf_nat_mangle_tcp_packet(pskb, ct, ctinfo, matchoff,
+					matchlen, buffer, strlen(buffer));
+}
+
+static int (*mangle[])(struct sk_buff **, __be32, u_int16_t,
+		       unsigned int, unsigned int, struct nf_conn *,
+		       enum ip_conntrack_info, u32 *seq)
+= {
+	[NF_CT_FTP_PORT] = mangle_rfc959_packet,
+	[NF_CT_FTP_PASV] = mangle_rfc959_packet,
+	[NF_CT_FTP_EPRT] = mangle_eprt_packet,
+	[NF_CT_FTP_EPSV] = mangle_epsv_packet
+};
+
+/* So, this packet has hit the connection tracking matching code.
+   Mangle it, and change the expectation to match the new version. */
+static unsigned int nf_nat_ftp(struct sk_buff **pskb,
+			       enum ip_conntrack_info ctinfo,
+			       enum nf_ct_ftp_type type,
+			       unsigned int matchoff,
+			       unsigned int matchlen,
+			       struct nf_conntrack_expect *exp,
+			       u32 *seq)
+{
+	__be32 newip;
+	u_int16_t port;
+	int dir = CTINFO2DIR(ctinfo);
+	struct nf_conn *ct = exp->master;
+
+	DEBUGP("FTP_NAT: type %i, off %u len %u\n", type, matchoff, matchlen);
+
+	/* Connection will come from wherever this packet goes, hence !dir */
+	newip = ct->tuplehash[!dir].tuple.dst.u3.ip;
+	exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
+	exp->dir = !dir;
+
+	/* When you see the packet, we need to NAT it the same as the
+	 * this one. */
+	exp->expectfn = nf_nat_follow_master;
+
+	/* Try to get same port: if not, try to change it. */
+	for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
+		exp->tuple.dst.u.tcp.port = htons(port);
+		if (nf_conntrack_expect_related(exp) == 0)
+			break;
+	}
+
+	if (port == 0)
+		return NF_DROP;
+
+	if (!mangle[type](pskb, newip, port, matchoff, matchlen, ct, ctinfo,
+			  seq)) {
+		nf_conntrack_unexpect_related(exp);
+		return NF_DROP;
+	}
+	return NF_ACCEPT;
+}
+
+static void __exit nf_nat_ftp_fini(void)
+{
+	rcu_assign_pointer(nf_nat_ftp_hook, NULL);
+	synchronize_rcu();
+}
+
+static int __init nf_nat_ftp_init(void)
+{
+	BUG_ON(rcu_dereference(nf_nat_ftp_hook));
+	rcu_assign_pointer(nf_nat_ftp_hook, nf_nat_ftp);
+	return 0;
+}
+
+/* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
+static int warn_set(const char *val, struct kernel_param *kp)
+{
+	printk(KERN_INFO KBUILD_MODNAME
+	       ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
+	return 0;
+}
+module_param_call(ports, warn_set, NULL, NULL, 0);
+
+module_init(nf_nat_ftp_init);
+module_exit(nf_nat_ftp_fini);