conntrackd: cthelper: add TFTP helper

This patch adds an userspace port of the TFTP helper that is currently
implemented in the kernel. This includes NAT support. It requires a
Linux kernel 3.12.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

3 files changed, 167 insertions, 0 deletions

diff --git a/src/expect.c b/src/expect.c
index 470b9ae..bba0ed7 100644
--- a/src/expect.c
+++ b/src/expect.c
@@ -212,3 +212,27 @@ cthelper_get_addr_dst(struct nf_conntrack *ct, int dir,
 		break;
 	}
 }
+
+void cthelper_get_port_src(struct nf_conntrack *ct, int dir, uint16_t *port)
+{
+	switch (dir) {
+	case MYCT_DIR_ORIG:
+		*port = nfct_get_attr_u16(ct, ATTR_PORT_SRC);
+		break;
+	case MYCT_DIR_REPL:
+		*port = nfct_get_attr_u16(ct, ATTR_REPL_PORT_SRC);
+		break;
+	}
+}
+
+void cthelper_get_port_dst(struct nf_conntrack *ct, int dir, uint16_t *port)
+{
+	switch (dir) {
+	case MYCT_DIR_ORIG:
+		*port = nfct_get_attr_u16(ct, ATTR_PORT_DST);
+		break;
+	case MYCT_DIR_REPL:
+		*port = nfct_get_attr_u16(ct, ATTR_REPL_PORT_DST);
+		break;
+	}
+}
diff --git a/src/helpers/Makefile.am b/src/helpers/Makefile.am
index ad380e3..216a5a7 100644
--- a/src/helpers/Makefile.am
+++ b/src/helpers/Makefile.am
@@ -3,6 +3,7 @@ include $(top_srcdir)/Make_global.am
 pkglib_LTLIBRARIES = ct_helper_dhcpv6.la \
 		     ct_helper_ftp.la	\
 		     ct_helper_rpc.la	\
+		     ct_helper_tftp.la	\
 		     ct_helper_tns.la	\
 		     ct_helper_sane.la
 
@@ -18,6 +19,10 @@ ct_helper_rpc_la_SOURCES = rpc.c
 ct_helper_rpc_la_LDFLAGS = -avoid-version -module $(LIBNETFILTER_CONNTRACK_LIBS)
 ct_helper_rpc_la_CFLAGS = $(AM_CFLAGS) $(LIBNETFILTER_CONNTRACK_CFLAGS)
 
+ct_helper_tftp_la_SOURCES = tftp.c
+ct_helper_tftp_la_LDFLAGS = -avoid-version -module $(LIBNETFILTER_CONNTRACK_LIBS)
+ct_helper_tftp_la_CFLAGS = $(AM_CFLAGS) $(LIBNETFILTER_CONNTRACK_CFLAGS)
+
 ct_helper_tns_la_SOURCES = tns.c
 ct_helper_tns_la_LDFLAGS = -avoid-version -module $(LIBNETFILTER_CONNTRACK_LIBS)
 ct_helper_tns_la_CFLAGS = $(AM_CFLAGS) $(LIBNETFILTER_CONNTRACK_CFLAGS)
diff --git a/src/helpers/tftp.c b/src/helpers/tftp.c
new file mode 100644
index 0000000..45591c6
--- /dev/null
+++ b/src/helpers/tftp.c
@@ -0,0 +1,138 @@
+/*
+ * (C) 2013 by Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * Adapted from:
+ *
+ * (C) 2001-2002 Magnus Boden <mb@ozaba.mine.nu>
+ * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
+ * 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 "conntrackd.h"
+#include "helper.h"
+#include "myct.h"
+#include "log.h"
+#include <errno.h>
+#include <netinet/ip.h>
+#include <netinet/ip6.h>
+#include <netinet/udp.h>
+#include <libmnl/libmnl.h>
+#include <libnetfilter_conntrack/libnetfilter_conntrack.h>
+#include <libnetfilter_queue/libnetfilter_queue.h>
+#include <libnetfilter_queue/libnetfilter_queue_udp.h>
+#include <libnetfilter_queue/pktbuff.h>
+#include <linux/netfilter.h>
+
+struct tftphdr {
+	uint16_t opcode;
+};
+
+#define TFTP_OPCODE_READ	1
+#define TFTP_OPCODE_WRITE	2
+#define TFTP_OPCODE_DATA	3
+#define TFTP_OPCODE_ACK		4
+#define TFTP_OPCODE_ERROR	5
+
+static unsigned int nat_tftp(struct pkt_buff *pkt, uint32_t ctinfo,
+			     struct nf_conntrack *ct, struct nf_expect *exp)
+{
+	struct nf_conntrack *nat_tuple;
+	static uint32_t zero[4] = { 0, 0, 0, 0 };
+
+	nat_tuple = nfct_new();
+	if (nat_tuple == NULL)
+		return NF_ACCEPT;
+
+	switch (nfct_get_attr_u8(ct, ATTR_L3PROTO)) {
+	case AF_INET:
+		nfct_set_attr_u8(nat_tuple, ATTR_L3PROTO, AF_INET);
+		nfct_set_attr_u32(nat_tuple, ATTR_IPV4_SRC, 0);
+		nfct_set_attr_u32(nat_tuple, ATTR_IPV4_DST, 0);
+		break;
+	case AF_INET6:
+		nfct_set_attr_u8(nat_tuple, ATTR_L3PROTO, AF_INET6);
+		nfct_set_attr(nat_tuple, ATTR_IPV6_SRC, &zero);
+		nfct_set_attr(nat_tuple, ATTR_IPV6_DST, &zero);
+		break;
+	}
+	nfct_set_attr_u8(nat_tuple, ATTR_L4PROTO, IPPROTO_UDP);
+	nfct_set_attr_u16(nat_tuple, ATTR_PORT_SRC,
+			  nfct_get_attr_u16(ct, ATTR_PORT_SRC));
+	nfct_set_attr_u16(nat_tuple, ATTR_PORT_DST, 0);
+
+	nfexp_set_attr_u32(exp, ATTR_EXP_NAT_DIR, MYCT_DIR_REPL);
+	nfexp_set_attr(exp, ATTR_EXP_FN, "nat-follow-master");
+	nfexp_set_attr(exp, ATTR_EXP_NAT_TUPLE, nat_tuple);
+
+	return NF_ACCEPT;
+}
+
+static int
+tftp_helper_cb(struct pkt_buff *pkt, uint32_t protoff,
+	       struct myct *myct, uint32_t ctinfo)
+{
+	const struct tftphdr *tfh;
+	struct nf_expect *exp;
+	unsigned int ret = NF_ACCEPT;
+	union nfct_attr_grp_addr saddr, daddr;
+	uint16_t dport;
+
+	tfh = (struct tftphdr *)(pktb_network_header(pkt) + protoff + sizeof(struct udphdr));
+
+	switch (ntohs(tfh->opcode)) {
+	case TFTP_OPCODE_READ:
+	case TFTP_OPCODE_WRITE:
+		/* RRQ and WRQ works the same way */
+		exp = nfexp_new();
+		if (exp == NULL) {
+			pr_debug("cannot alloc expectation\n");
+			return NF_DROP;
+		}
+
+		cthelper_get_addr_src(myct->ct, MYCT_DIR_REPL, &saddr);
+		cthelper_get_addr_dst(myct->ct, MYCT_DIR_REPL, &daddr);
+		cthelper_get_port_dst(myct->ct, MYCT_DIR_REPL, &dport);
+
+		if (cthelper_expect_init(exp, myct->ct, 0, &saddr, &daddr,
+					 IPPROTO_UDP, NULL, &dport, 0)) {
+			nfexp_destroy(exp);
+			return NF_DROP;
+		}
+
+		if (nfct_get_attr_u32(myct->ct, ATTR_STATUS) & IPS_NAT_MASK)
+			ret = nat_tftp(pkt, ctinfo, myct->ct, exp);
+
+		myct->exp = exp;
+		break;
+	case TFTP_OPCODE_DATA:
+	case TFTP_OPCODE_ACK:
+		pr_debug("Data/ACK opcode\n");
+		break;
+	case TFTP_OPCODE_ERROR:
+		pr_debug("Error opcode\n");
+		break;
+	default:
+		pr_debug("Unknown opcode\n");
+	}
+	return ret;
+}
+
+static struct ctd_helper tftp_helper = {
+	.name		= "tftp",
+	.l4proto	= IPPROTO_UDP,
+	.cb		= tftp_helper_cb,
+	.policy		= {
+		[0] = {
+			.name			= "tftp",
+			.expect_max		= 1,
+			.expect_timeout		= 5 * 60,
+		},
+	},
+};
+
+static void __attribute__ ((constructor)) tftp_init(void)
+{
+	helper_register(&tftp_helper);
+}