owfd: dhcp: implement basic DHCP client

Implement the --client option and spawn gdhcp_client accordingly. Once we
get a lease, set the information via "ip" for the given network interface.

Note that we don't support any routing/gateways, DNS or other stuff. This
is not needed for WFD so it's unlikely to get implemented. Ever.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

1 files changed, 303 insertions, 1 deletions

diff --git a/src/dhcp.c b/src/dhcp.c
index 5b37f5f..58a63eb 100644
--- a/src/dhcp.c
+++ b/src/dhcp.c
@@ -23,6 +23,29 @@
  * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  */
 
+/*
+ * Small DHCP Client/Server for OpenWFD
+ * Wifi-P2P requires us to use DHCP to set up a private P2P network. As all
+ * DHCP daemons available have horrible interfaces for ad-hoc setups, we have
+ * this small replacement for all DHCP operations.
+ *
+ * This program implements a DHCP server and daemon. See --help for usage
+ * information. We build on gdhcp from connman as the underlying DHCP protocol
+ * implementation. To configure network devices, we actually invoke the "ip"
+ * binary.
+ *
+ * Note that this is a gross hack! We don't intend to provide a fully functional
+ * DHCP server or client here. This is only a replacement for the current lack
+ * of Wifi-P2P support in common network managers. Once they gain proper
+ * support, we will drop this helper!
+ *
+ * The "ip" invokation is quite fragile and ugly. However, performing these
+ * steps directly involves netlink operations and more. As no-one came up with
+ * patches, yet, we keep the hack. To anyone trying to fix it: Please, spend
+ * this time hacking on NetworkManager, connman and friends instead! If they
+ * gain Wifi-P2P support, this whole thing will get trashed.
+ */
+
 #include <arpa/inet.h>
 #include <errno.h>
 #include <glib.h>
@@ -35,6 +58,7 @@
 #include <sys/epoll.h>
 #include <sys/signalfd.h>
 #include <sys/socket.h>
+#include <sys/wait.h>
 #include <unistd.h>
 #include "dhcp.h"
 #include "gdhcp/gdhcp.h"
@@ -50,8 +74,202 @@ struct owfd_dhcp {
 	int sfd;
 	GIOChannel *sfd_chan;
 	guint sfd_id;
+
+	GDHCPClient *client;
+	char *client_addr;
 };
 
+static int flush_if_addr(struct owfd_dhcp *dhcp)
+{
+	char *argv[64];
+	int i, r;
+	pid_t pid, rp;
+	sigset_t mask;
+
+	pid = fork();
+	if (pid < 0) {
+		return log_ERRNO();
+	} else if (!pid) {
+		/* child */
+
+		sigemptyset(&mask);
+		sigprocmask(SIG_SETMASK, &mask, NULL);
+
+		/* redirect stdout to stderr */
+		dup2(2, 1);
+
+		i = 0;
+		argv[i++] = dhcp->config.ip_binary;
+		argv[i++] = "addr";
+		argv[i++] = "flush";
+		argv[i++] = "dev";
+		argv[i++] = dhcp->config.interface;
+		argv[i++] = "label";
+		argv[i++] = dhcp->iflabel;
+		argv[i] = NULL;
+
+		execve(argv[0], argv, environ);
+		_exit(1);
+	}
+
+	log_info("flushing local if-addr");
+	rp = waitpid(pid, &r, 0);
+	if (rp != pid) {
+		log_error("cannot flush local if-addr via '%s'",
+			  dhcp->config.ip_binary);
+		return -EFAULT;
+	} else if (!WIFEXITED(r)) {
+		log_error("flushing local if-addr via '%s' failed",
+			  dhcp->config.ip_binary);
+		return -EFAULT;
+	} else if (WEXITSTATUS(r)) {
+		log_error("flushing local if-addr via '%s' failed with: %d",
+			  dhcp->config.ip_binary, WEXITSTATUS(r));
+		return -EFAULT;
+	}
+
+	log_debug("successfully flushed local if-addr via %s",
+		  dhcp->config.ip_binary);
+
+	return 0;
+}
+
+static int add_if_addr(struct owfd_dhcp *dhcp, char *addr)
+{
+	char *argv[64];
+	int i, r;
+	pid_t pid, rp;
+	sigset_t mask;
+
+	pid = fork();
+	if (pid < 0) {
+		return log_ERRNO();
+	} else if (!pid) {
+		/* child */
+
+		sigemptyset(&mask);
+		sigprocmask(SIG_SETMASK, &mask, NULL);
+
+		/* redirect stdout to stderr */
+		dup2(2, 1);
+
+		i = 0;
+		argv[i++] = dhcp->config.ip_binary;
+		argv[i++] = "addr";
+		argv[i++] = "add";
+		argv[i++] = addr;
+		argv[i++] = "dev";
+		argv[i++] = dhcp->config.interface;
+		argv[i++] = "label";
+		argv[i++] = dhcp->iflabel;
+		argv[i] = NULL;
+
+		execve(argv[0], argv, environ);
+		_exit(1);
+	}
+
+	log_info("adding local if-addr %s", addr);
+	rp = waitpid(pid, &r, 0);
+	if (rp != pid) {
+		log_error("cannot set local if-addr %s via '%s'",
+			  addr, dhcp->config.ip_binary);
+		return -EFAULT;
+	} else if (!WIFEXITED(r)) {
+		log_error("setting local if-addr %s via '%s' failed",
+			  addr, dhcp->config.ip_binary);
+		return -EFAULT;
+	} else if (WEXITSTATUS(r)) {
+		log_error("setting local if-addr %s via '%s' failed with: %d",
+			  addr, dhcp->config.ip_binary, WEXITSTATUS(r));
+		return -EFAULT;
+	}
+
+	log_debug("successfully set local if-addr %s via %s",
+		  addr, dhcp->config.ip_binary);
+
+	return 0;
+}
+
+static void client_lease_fn(GDHCPClient *client, gpointer data)
+{
+	struct owfd_dhcp *dhcp = data;
+	char *addr, *a, *subnet = NULL;
+	GList *l;
+	int r;
+
+	log_info("lease available");
+
+	addr = g_dhcp_client_get_address(client);
+	log_info("lease: address: %s", addr);
+
+	l = g_dhcp_client_get_option(client, G_DHCP_SUBNET);
+	for ( ; l; l = l->next) {
+		subnet = subnet ? : (char*)l->data;
+		log_info("lease: subnet: %s", (char*)l->data);
+	}
+
+	l = g_dhcp_client_get_option(client, G_DHCP_DNS_SERVER);
+	for ( ; l; l = l->next)
+		log_info("lease: dns-server: %s", (char*)l->data);
+
+	l = g_dhcp_client_get_option(client, G_DHCP_ROUTER);
+	for ( ; l; l = l->next)
+		log_info("lease: router: %s", (char*)l->data);
+
+	if (!addr) {
+		log_error("lease without IP address");
+		goto error;
+	}
+	if (!subnet) {
+		log_warning("lease without subnet mask, using 24");
+		subnet = "24";
+	}
+
+	r = asprintf(&a, "%s/%s", addr, subnet);
+	if (r < 0) {
+		log_vENOMEM();
+		g_free(addr);
+		goto error;
+	} else {
+		g_free(addr);
+	}
+
+	if (dhcp->client_addr && !strcmp(dhcp->client_addr, a)) {
+		log_info("given address already set");
+		free(a);
+	} else {
+		free(dhcp->client_addr);
+		dhcp->client_addr = a;
+
+		r = flush_if_addr(dhcp);
+		if (r < 0) {
+			log_error("cannot flush addr on local interface %s",
+				  dhcp->config.interface);
+			goto error;
+		}
+
+		r = add_if_addr(dhcp, dhcp->client_addr);
+		if (r < 0) {
+			log_error("cannot set parameters on local interface %s",
+				  dhcp->config.interface);
+			goto error;
+		}
+	}
+
+	return;
+
+error:
+	g_main_loop_quit(dhcp->loop);
+}
+
+static void client_no_lease_fn(GDHCPClient *client, gpointer data)
+{
+	struct owfd_dhcp *dhcp = data;
+
+	log_error("no lease available");
+	g_main_loop_quit(dhcp->loop);
+}
+
 static gboolean owfd_dhcp_sfd_fn(GIOChannel *chan, GIOCondition mask,
 				 gpointer data)
 {
@@ -84,6 +302,22 @@ static gboolean owfd_dhcp_sfd_fn(GIOChannel *chan, GIOCondition mask,
 
 static int owfd_dhcp_run(struct owfd_dhcp *dhcp)
 {
+	int r;
+
+	if (dhcp->config.client) {
+		log_info("running dhcp client on %s via '%s'",
+			 dhcp->config.interface, dhcp->config.ip_binary);
+
+		r = g_dhcp_client_start(dhcp->client, NULL);
+		if (r != 0) {
+			log_error("cannot start DHCP client: %d", r);
+			return -EFAULT;
+		}
+	} else {
+		log_info("running dhcp server on %s via '%s'",
+			 dhcp->config.interface, dhcp->config.ip_binary);
+	}
+
 	g_main_loop_run(dhcp->loop);
 
 	return 0;
@@ -91,6 +325,20 @@ static int owfd_dhcp_run(struct owfd_dhcp *dhcp)
 
 static void owfd_dhcp_teardown(struct owfd_dhcp *dhcp)
 {
+	if (dhcp->config.client) {
+		if (dhcp->client) {
+			g_dhcp_client_stop(dhcp->client);
+
+			if (dhcp->client_addr) {
+				flush_if_addr(dhcp);
+				free(dhcp->client_addr);
+			}
+
+			g_dhcp_client_unref(dhcp->client);
+		}
+	} else {
+	}
+
 	if (dhcp->sfd >= 0) {
 		g_source_remove(dhcp->sfd_id);
 		g_io_channel_unref(dhcp->sfd_chan);
@@ -120,6 +368,7 @@ static int owfd_dhcp_setup(struct owfd_dhcp *dhcp)
 	int r, i;
 	sigset_t mask;
 	struct sigaction sig;
+	GDHCPClientError cerr;
 
 	if (geteuid())
 		log_warning("not running as uid=0, dhcp might not work");
@@ -172,6 +421,60 @@ static int owfd_dhcp_setup(struct owfd_dhcp *dhcp)
 				      owfd_dhcp_sfd_fn,
 				      dhcp);
 
+	if (dhcp->config.client) {
+		dhcp->client = g_dhcp_client_new(G_DHCP_IPV4, dhcp->ifindex,
+						 &cerr);
+		if (!dhcp->client) {
+			r = -EINVAL;
+
+			switch (cerr) {
+			case G_DHCP_CLIENT_ERROR_INTERFACE_UNAVAILABLE:
+				log_error("cannot create GDHCP client: interface %s unavailable",
+					  dhcp->config.interface);
+				break;
+			case G_DHCP_CLIENT_ERROR_INTERFACE_IN_USE:
+				log_error("cannot create GDHCP client: interface %s in use",
+					  dhcp->config.interface);
+				break;
+			case G_DHCP_CLIENT_ERROR_INTERFACE_DOWN:
+				log_error("cannot create GDHCP client: interface %s down",
+					  dhcp->config.interface);
+				break;
+			case G_DHCP_CLIENT_ERROR_NOMEM:
+				r = log_ENOMEM();
+				break;
+			case G_DHCP_CLIENT_ERROR_INVALID_INDEX:
+				log_error("cannot create GDHCP client: invalid interface %s",
+					  dhcp->config.interface);
+				break;
+			case G_DHCP_CLIENT_ERROR_INVALID_OPTION:
+				log_error("cannot create GDHCP client: invalid options");
+				break;
+			default:
+				log_error("cannot create GDHCP client (%d)",
+					  cerr);
+				break;
+			}
+
+			goto error;
+		}
+
+		g_dhcp_client_set_send(dhcp->client, G_DHCP_HOST_NAME,
+				       "<hostname>");
+
+		g_dhcp_client_set_request(dhcp->client, G_DHCP_SUBNET);
+		g_dhcp_client_set_request(dhcp->client, G_DHCP_DNS_SERVER);
+		g_dhcp_client_set_request(dhcp->client, G_DHCP_ROUTER);
+
+		g_dhcp_client_register_event(dhcp->client,
+					     G_DHCP_CLIENT_EVENT_LEASE_AVAILABLE,
+					     client_lease_fn, dhcp);
+		g_dhcp_client_register_event(dhcp->client,
+					     G_DHCP_CLIENT_EVENT_NO_LEASE,
+					     client_no_lease_fn, dhcp);
+	} else {
+	}
+
 	return 0;
 
 error:
@@ -211,7 +514,6 @@ int main(int argc, char **argv)
 	if (r < 0)
 		goto err_conf;
 
-	log_info("running");
 	r = owfd_dhcp_run(&dhcp);
 
 	owfd_dhcp_teardown(&dhcp);