conntrackd: add cthelper infrastructure (+ example FTP helper)

This patch adds the user-space helper infrastructure. It also
contains the implementation of the FTP helper in user-space.

There's one example file that you can use to configure conntrackd
as user-space connection tracking helper under:

 doc/helper/conntrackd.conf

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

1 files changed, 521 insertions, 0 deletions

diff --git a/src/cthelper.c b/src/cthelper.c
new file mode 100644
index 0000000..c119869
--- /dev/null
+++ b/src/cthelper.c
@@ -0,0 +1,521 @@
+/*
+ * (C) 2006-2012 by Pablo Neira Ayuso <pablo@netfilter.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ * This code has been sponsored by Vyatta Inc. <http://www.vyatta.com>
+ */
+
+#include "conntrackd.h"
+#include "log.h"
+#include "fds.h"
+#include "helper.h"
+
+#include <unistd.h>
+#include <fcntl.h>
+#include <time.h>
+#include <errno.h>
+
+#include <netinet/in.h>
+#include <netinet/ip.h>
+#include <netinet/tcp.h>
+#include <netinet/udp.h>
+#include <net/ethernet.h>
+
+#ifndef __aligned_be64
+#define __aligned_be64 unsigned long long __attribute__((aligned(8)))
+#endif
+
+#include <linux/netfilter/nfnetlink_queue.h>
+
+#include <libmnl/libmnl.h>
+#include <libnetfilter_queue/libnetfilter_queue.h>
+#include <libnetfilter_queue/pktbuff.h>
+#include <libnetfilter_cthelper/libnetfilter_cthelper.h>
+#include <linux/netfilter.h>
+#include <libnetfilter_queue/pktbuff.h>
+
+void cthelper_kill(void)
+{
+	mnl_socket_close(STATE_CTH(nl));
+	free(state.cthelper);
+}
+
+int cthelper_local(int fd, int type, void *data)
+{
+	/* No services to obtain information on helpers yet, sorry */
+	return LOCAL_RET_OK;
+}
+
+static struct nlmsghdr *
+nfq_hdr_put(char *buf, int type, uint32_t queue_num)
+{
+	struct nlmsghdr *nlh = mnl_nlmsg_put_header(buf);
+	nlh->nlmsg_type = (NFNL_SUBSYS_QUEUE << 8) | type;
+	nlh->nlmsg_flags = NLM_F_REQUEST;
+
+	struct nfgenmsg *nfg = mnl_nlmsg_put_extra_header(nlh, sizeof(*nfg));
+	nfg->nfgen_family = AF_UNSPEC;
+	nfg->version = NFNETLINK_V0;
+	nfg->res_id = htons(queue_num);
+
+	return nlh;
+}
+
+static int
+pkt_get(void *pkt, uint32_t pktlen, uint16_t proto, uint32_t *protoff)
+{
+	switch(proto) {
+	case ETHERTYPE_IP: {
+		struct iphdr *ip = (struct iphdr *) pkt;
+
+		/* No room for IPv4 header. */
+		if (pktlen < sizeof(struct iphdr)) {
+			dlog(LOG_ERR, "no room for IPv4 header");
+			return -1;
+		}
+
+		/* this is not IPv4, skip. */
+		if (ip->version != 4) {
+			dlog(LOG_ERR, "not IPv4, skipping");
+			return -1;
+		}
+
+		*protoff = 4 * ip->ihl;
+
+		switch (ip->protocol) {
+		case IPPROTO_TCP: {
+			struct tcphdr *tcph =
+				(struct tcphdr *) ((char *)pkt + *protoff);
+
+			/* No room for IPv4 header plus TCP header. */
+			if (pktlen < *protoff + sizeof(struct tcphdr)
+			    || pktlen < *protoff + tcph->doff * 4) {
+				dlog(LOG_ERR, "no room for IPv4 + TCP header, skip");
+				return -1;
+			}
+			return 0;
+		}
+		case IPPROTO_UDP:
+			/* No room for IPv4 header plus UDP header. */
+			if (pktlen < *protoff + sizeof(struct udphdr)) {
+				dlog(LOG_ERR, "no room for IPv4 + UDP header, skip");
+				return -1;
+			}
+			return 0;
+		default:
+			dlog(LOG_ERR, "not TCP/UDP, skipping");
+			return -1;
+		}
+		break;
+	}
+	case ETHERTYPE_IPV6:
+		dlog(LOG_ERR, "no IPv6 support sorry");
+		return 0;
+	default:
+		/* Unknown layer 3 protocol. */
+		dlog(LOG_ERR, "unknown layer 3 protocol (%d), skipping", proto);
+		return -1;
+	}
+	return 0;
+}
+
+static int
+pkt_verdict_issue(struct ctd_helper_instance *cur, struct myct *myct,
+		  uint16_t queue_num, uint32_t id, uint32_t verdict,
+		  struct pkt_buff *pktb)
+{
+	struct nlmsghdr *nlh;
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlattr *nest;
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_VERDICT, queue_num);
+
+	/* save private data and send it back to kernel-space. */
+	nfct_set_attr_l(myct->ct, ATTR_HELPER_INFO, myct->priv_data,
+			cur->helper->priv_data_len);
+
+	nfq_nlmsg_verdict_put(nlh, id, verdict);
+	if (pktb_mangled(pktb))
+		nfq_nlmsg_verdict_put_pkt(nlh, pktb_data(pktb), pktb_len(pktb));
+
+	nest = mnl_attr_nest_start(nlh, NFQA_CT);
+	if (nest == NULL)
+		return -1;
+
+	nfct_nlmsg_build(nlh, myct->ct);
+	mnl_attr_nest_end(nlh, nest);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send verdict: %s", strerror(errno));
+		return -1;
+	}
+
+	return 0;
+}
+
+static int
+pkt_verdict_error(uint16_t queue_num, uint32_t id)
+{
+	struct nlmsghdr *nlh;
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_VERDICT, queue_num);
+	nfq_nlmsg_verdict_put(nlh, id, NF_ACCEPT);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send verdict: %s", strerror(errno));
+		return -1;
+	}
+	return 0;
+}
+
+static struct ctd_helper_instance *
+helper_run(struct pkt_buff *pktb, uint32_t protoff, struct myct *myct,
+	   uint32_t ctinfo, uint32_t queue_num, int *verdict)
+{
+	struct ctd_helper_instance *cur, *helper = NULL;
+
+	list_for_each_entry(cur, &CONFIG(cthelper).list, head) {
+		if (cur->queue_num == queue_num) {
+			const void *priv_data;
+
+			/* retrieve helper private data. */
+			priv_data = nfct_get_attr(myct->ct, ATTR_HELPER_INFO);
+			if (priv_data != NULL) {
+				myct->priv_data =
+					calloc(1, cur->helper->priv_data_len);
+
+				if (myct->priv_data == NULL)
+					continue;
+
+				memcpy(myct->priv_data, priv_data,
+					cur->helper->priv_data_len);
+			}
+
+			*verdict = cur->helper->cb(pktb, protoff, myct, ctinfo);
+			helper = cur;
+			break;
+		}
+	}
+	return helper;
+}
+
+static int nfq_queue_cb(const struct nlmsghdr *nlh, void *data)
+{
+	struct nfqnl_msg_packet_hdr *ph = NULL;
+	struct nlattr *attr[NFQA_MAX+1] = {};
+	struct nfgenmsg *nfg;
+	uint8_t *pkt;
+	uint16_t l3num;
+	uint32_t id, ctinfo, queue_num = 0, protoff = 0, pktlen;
+	struct nf_conntrack *ct = NULL;
+	struct myct *myct;
+	struct ctd_helper_instance *helper;
+	struct pkt_buff *pktb;
+	int verdict = NF_ACCEPT;
+
+	if (nfq_nlmsg_parse(nlh, attr) < 0) {
+		dlog(LOG_ERR, "problems parsing message from kernel");
+		return MNL_CB_ERROR;
+	}
+
+	ph = (struct nfqnl_msg_packet_hdr *)
+		mnl_attr_get_payload(attr[NFQA_PACKET_HDR]);
+	if (ph == NULL) {
+		dlog(LOG_ERR, "problems retrieving metaheader");
+		return MNL_CB_ERROR;
+	}
+
+	id = ntohl(ph->packet_id);
+
+	if (!attr[NFQA_PAYLOAD]) {
+		dlog(LOG_ERR, "packet with no payload");
+		goto err;
+	}
+	if (!attr[NFQA_CT] || !attr[NFQA_CT_INFO]) {
+		dlog(LOG_ERR, "no CT attached to this packet");
+		goto err;
+	}
+
+	pkt = mnl_attr_get_payload(attr[NFQA_PAYLOAD]);
+	pktlen = mnl_attr_get_payload_len(attr[NFQA_PAYLOAD]);
+
+	nfg = mnl_nlmsg_get_payload(nlh);
+	l3num = nfg->nfgen_family;
+	queue_num = ntohs(nfg->res_id);
+
+	if (pkt_get(pkt, pktlen, ntohs(ph->hw_protocol), &protoff))
+		goto err;
+
+	ct = nfct_new();
+	if (ct == NULL)
+		goto err;
+
+	if (nfct_payload_parse(mnl_attr_get_payload(attr[NFQA_CT]),
+			       mnl_attr_get_payload_len(attr[NFQA_CT]),
+			       l3num, ct) < 0) {
+		dlog(LOG_ERR, "cannot convert message to CT");
+		goto err;
+	}
+
+	myct = calloc(1, sizeof(struct myct));
+	if (myct == NULL)
+		goto err;
+
+	myct->ct = ct;
+	ctinfo = ntohl(mnl_attr_get_u32(attr[NFQA_CT_INFO]));
+
+	/* XXX: 256 bytes enough for possible NAT mangling in helpers? */
+	pktb = pktb_alloc(AF_INET, pkt, pktlen, 256);
+	if (pktb == NULL)
+		goto err;
+
+	/* Misconfiguration: if no helper found, accept the packet. */
+	helper = helper_run(pktb, protoff, myct, ctinfo, queue_num, &verdict);
+	if (!helper)
+		goto err_pktb;
+
+	if (pkt_verdict_issue(helper, myct, queue_num, id, verdict, pktb) < 0)
+		goto err_pktb;
+
+	if (ct != NULL)
+		nfct_destroy(ct);
+	if (myct && myct->priv_data != NULL)
+		free(myct->priv_data);
+	if (myct != NULL)
+		free(myct);
+
+	return MNL_CB_OK;
+err_pktb:
+	pktb_free(pktb);
+err:
+	/* In case of error, we don't want to disrupt traffic. We accept all.
+	 * This is connection tracking after all. The policy is not to drop
+	 * packet unless we enter some inconsistent state.
+	 */
+	pkt_verdict_error(queue_num, id);
+
+	if (ct != NULL)
+		nfct_destroy(ct);
+
+	return MNL_CB_OK;
+}
+
+static void nfq_cb(void *data)
+{
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	int ret;
+
+	ret = mnl_socket_recvfrom(STATE_CTH(nl), buf, sizeof(buf));
+	if (ret == -1) {
+		dlog(LOG_ERR, "failed to receive message: %s", strerror(errno));
+		return;
+	}
+
+	ret = mnl_cb_run(buf, ret, 0, STATE_CTH(portid), nfq_queue_cb, NULL);
+	if (ret < 0){
+		dlog(LOG_ERR, "failed to process message");
+		return;
+	}
+}
+
+static int cthelper_setup(struct ctd_helper_instance *cur)
+{
+	struct nfct_helper *t;
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh;
+	uint32_t seq;
+	int j, ret;
+
+	t = nfct_helper_alloc();
+	if (t == NULL) {
+		dlog(LOG_ERR, "cannot allocate object for helper");
+		return -1;
+	}
+
+	nfct_helper_attr_set(t, NFCTH_ATTR_NAME, cur->helper->name);
+	nfct_helper_attr_set_u32(t, NFCTH_ATTR_QUEUE_NUM, cur->queue_num);
+	nfct_helper_attr_set_u16(t, NFCTH_ATTR_PROTO_L3NUM, cur->l3proto);
+	nfct_helper_attr_set_u8(t, NFCTH_ATTR_PROTO_L4NUM, cur->l4proto);
+	nfct_helper_attr_set_u32(t, NFCTH_ATTR_STATUS,
+					NFCT_HELPER_STATUS_ENABLED);
+
+	dlog(LOG_NOTICE, "configuring helper `%s' with queuenum=%d",
+		cur->helper->name, cur->queue_num);
+
+	for (j=0; j<CTD_HELPER_POLICY_MAX; j++) {
+		struct nfct_helper_policy *p;
+
+		if (!cur->helper->policy[j].name[0])
+			break;
+
+		p = nfct_helper_policy_alloc();
+		if (p == NULL) {
+			dlog(LOG_ERR, "cannot allocate object for helper");
+			return -1;
+		}
+		/* FIXME: get existing policy values from the kernel first. */
+		nfct_helper_policy_attr_set(p, NFCTH_ATTR_POLICY_NAME,
+					cur->helper->policy[j].name);
+		nfct_helper_policy_attr_set_u32(p, NFCTH_ATTR_POLICY_TIMEOUT,
+					cur->helper->policy[j].expect_timeout);
+		nfct_helper_policy_attr_set_u32(p, NFCTH_ATTR_POLICY_MAX,
+					cur->helper->policy[j].expect_max);
+
+		dlog(LOG_NOTICE, "policy name=%s expect_timeout=%d expect_max=%d",
+			cur->helper->policy[j].name,
+			cur->helper->policy[j].expect_timeout,
+			cur->helper->policy[j].expect_max);
+
+		nfct_helper_attr_set(t, NFCTH_ATTR_POLICY+j, p);
+	}
+
+	if (j == 0) {
+		dlog(LOG_ERR, "you have to define one policy for helper");
+		return -1;
+	}
+
+	seq = time(NULL);
+	nlh = nfct_helper_nlmsg_build_hdr(buf, NFNL_MSG_CTHELPER_NEW,
+					  NLM_F_CREATE | NLM_F_ACK, seq);
+	nfct_helper_nlmsg_build_payload(nlh, t);
+
+	nfct_helper_free(t);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "sending cthelper configuration");
+		return -1;
+	}
+
+	ret = mnl_socket_recvfrom(STATE_CTH(nl), buf, sizeof(buf));
+	while (ret > 0) {
+		ret = mnl_cb_run(buf, ret, seq, STATE_CTH(portid), NULL, NULL);
+		if (ret <= 0)
+			break;
+		ret = mnl_socket_recvfrom(STATE_CTH(nl), buf, sizeof(buf));
+	}
+	if (ret == -1) {
+		dlog(LOG_ERR, "trying to configure cthelper `%s': %s",
+			cur->helper->name, strerror(errno));
+		return -1;
+	}
+
+	return 0;
+}
+
+static int cthelper_nfqueue_setup(struct ctd_helper_instance *cur)
+{
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh;
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, cur->queue_num);
+	nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_BIND);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send bind command");
+		return -1;
+	}
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, cur->queue_num);
+	nfq_nlmsg_cfg_put_params(nlh, NFQNL_COPY_PACKET, 0xffff);
+	mnl_attr_put_u32(nlh, NFQA_CFG_FLAGS, htonl(NFQA_CFG_F_CONNTRACK));
+	mnl_attr_put_u32(nlh, NFQA_CFG_MASK, htonl(0xffffffff));
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send configuration");
+		return -1;
+	}
+
+	return 0;
+}
+
+static int cthelper_configure(struct ctd_helper_instance *cur)
+{
+	/* First, configure cthelper. */
+	if (cthelper_setup(cur) < 0)
+		return -1;
+
+	/* Now, we are ready to configure nfqueue attached to this helper. */
+	if (cthelper_nfqueue_setup(cur) < 0)
+		return -1;
+
+	dlog(LOG_NOTICE, "helper `%s' configured successfully",
+		cur->helper->name);
+
+	return 0;
+}
+
+static int nfq_configure(void)
+{
+	char buf[MNL_SOCKET_BUFFER_SIZE];
+	struct nlmsghdr *nlh;
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, 0);
+	nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_PF_UNBIND);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send pf unbind command");
+		return -1;
+	}
+
+	nlh = nfq_hdr_put(buf, NFQNL_MSG_CONFIG, 0);
+	nfq_nlmsg_cfg_put_cmd(nlh, AF_INET, NFQNL_CFG_CMD_PF_BIND);
+
+	if (mnl_socket_sendto(STATE_CTH(nl), nlh, nlh->nlmsg_len) < 0) {
+		dlog(LOG_ERR, "failed to send pf bind command");
+		return -1;
+	}
+
+	return 0;
+}
+
+int cthelper_init(void)
+{
+	struct ctd_helper_instance *cur;
+	int ret;
+
+	state.cthelper = calloc(1, sizeof(struct ct_helper_state));
+	if (state.cthelper == NULL) {
+		dlog(LOG_ERR, "can't allocate memory for cthelper struct");
+		return -1;
+	}
+
+	STATE_CTH(nl) = mnl_socket_open(NETLINK_NETFILTER);
+	if (STATE_CTH(nl) == NULL) {
+		dlog(LOG_ERR, "cannot open nfq socket");
+		return -1;
+	}
+	fcntl(mnl_socket_get_fd(STATE_CTH(nl)), F_SETFL, O_NONBLOCK);
+
+	if (mnl_socket_bind(STATE_CTH(nl), 0, MNL_SOCKET_AUTOPID) < 0) {
+		dlog(LOG_ERR, "cannot bind nfq socket");
+		return -1;
+	}
+	STATE_CTH(portid) = mnl_socket_get_portid(STATE_CTH(nl));
+
+	if (nfq_configure())
+		return -1;
+
+	list_for_each_entry(cur, &CONFIG(cthelper).list, head) {
+		ret = cthelper_configure(cur);
+		if (ret < 0)
+			return ret;
+	}
+
+	register_fd(mnl_socket_get_fd(STATE_CTH(nl)), nfq_cb, NULL, STATE(fds));
+
+	return 0;
+}