tun: Export setup_tun() functionality

Create three new setup_tun() library functions:

    openconnect_setup_tun_device - create a tun device
    openconnect_setup_tun_script - pass traffic through a script
    openconnect_setup_tun_fd - pass traffic through an existing fd

The latter is needed to support Android's VpnService API.  If a fd is
passed in, the library will not close it.

In all cases, the caller no longer needs to directly manipulate
vpninfo->vpnc_script or vpninfo->script_tun.  The former is treated as
a standard caller-allocated, library-freed string.

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>

libopenconnect.map.in

@@ -39,6 +39,9 @@ OPENCONNECT_3.1 {
  global:
 	openconnect_setup_cmd_pipe;
 	openconnect_mainloop;
+	openconnect_setup_tun_device;
+	openconnect_setup_tun_script;
+	openconnect_setup_tun_fd;
 } OPENCONNECT_3.0;
 
 OPENCONNECT_PRIVATE {

library.c

@@ -123,6 +123,8 @@ void openconnect_vpninfo_free(struct openconnect_info *vpninfo)
 	free(vpninfo->redirect_url);
 	free(vpninfo->proxy_type);
 	free(vpninfo->proxy);
+	free(vpninfo->vpnc_script);
+	free(vpninfo->ifname);
 
 	if (vpninfo->csd_scriptname) {
 		unlink(vpninfo->csd_scriptname);

main.c

@@ -508,6 +508,8 @@ int main(int argc, char **argv)
 	int use_syslog = 0;
 	char *urlpath = NULL;
 	char *proxy = getenv("https_proxy");
+	int script_tun = 0;
+	char *vpnc_script = NULL, *ifname = NULL;
 	int autoproxy = 0;
 	uid_t uid = getuid();
 	int opt;
@@ -554,7 +556,6 @@ int main(int argc, char **argv)
 	vpninfo->process_auth_form = process_auth_form_cb;
 	vpninfo->cbdata = vpninfo;
 	vpninfo->cert_expire_warning = 60 * 86400;
-	vpninfo->vpnc_script = DEFAULT_VPNCSCRIPT;
 	vpninfo->cmd_fd = -1;
 	vpninfo->xmlpost = 1;
 
@@ -659,7 +660,7 @@ int main(int argc, char **argv)
 		case 'h':
 			usage();
 		case 'i':
-			vpninfo->ifname = keep_config_arg();
+			ifname = xstrdup(config_arg);
 			break;
 		case 'l':
 			use_syslog = 1;
@@ -703,10 +704,10 @@ int main(int argc, char **argv)
 			nocertcheck = 1;
 			break;
 		case 's':
-			vpninfo->vpnc_script = keep_config_arg();
+			vpnc_script = xstrdup(config_arg);
 			break;
 		case 'S':
-			vpninfo->script_tun = 1;
+			script_tun = 1;
 			break;
 		case 'u':
 			free(username);
@@ -922,7 +923,14 @@ int main(int argc, char **argv)
 		exit(1);
 	}
 
-	if (setup_tun(vpninfo)) {
+	if (!vpnc_script)
+		vpnc_script = xstrdup(DEFAULT_VPNCSCRIPT);
+	if (script_tun) {
+		if (openconnect_setup_tun_script(vpninfo, vpnc_script)) {
+			fprintf(stderr, _("Set up tun script failed\n"));
+			exit(1);
+		}
+	} else if (openconnect_setup_tun_device(vpninfo, vpnc_script, ifname)) {
 		fprintf(stderr, _("Set up tun device failed\n"));
 		exit(1);
 	}

openconnect-internal.h

@@ -263,7 +263,7 @@ struct openconnect_info {
 	unsigned char dtls_secret[48];
 
 	char *dtls_cipher;
-	const char *vpnc_script;
+	char *vpnc_script;
 	int script_tun;
 	char *ifname;
 
@@ -371,7 +371,6 @@ char *openconnect__strcasestr(const char *haystack, const char *needle);
 /****************************************************************************/
 
 /* tun.c */
-int setup_tun(struct openconnect_info *vpninfo);
 int tun_mainloop(struct openconnect_info *vpninfo, int *timeout);
 void shutdown_tun(struct openconnect_info *vpninfo);
 int script_config_tun(struct openconnect_info *vpninfo, const char *reason);

openconnect.h

@@ -261,6 +261,16 @@ int openconnect_setup_cmd_pipe(struct openconnect_info *vpninfo);
 
 const char *openconnect_get_version(void);
 
+/* Create a tun device through the OS kernel (typical use case). Both
+   strings are optional and can be NULL if desired. */
+int openconnect_setup_tun_device(struct openconnect_info *vpninfo, char *vpnc_script, char *ifname);
+
+/* Pass traffic to a script program (no tun device). */
+int openconnect_setup_tun_script(struct openconnect_info *vpninfo, char *tun_script);
+
+/* Caller will provide a file descriptor for the tunnel traffic. */
+int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, int tun_fd);
+
 /* Start the main loop; exits if OC_CMD_CANCEL is received on cmd_fd or
    the remote site aborts. */
 int openconnect_mainloop(struct openconnect_info *vpninfo,

tun.c

@@ -631,64 +631,78 @@ static int os_setup_tun(struct openconnect_info *vpninfo)
 	return tun_fd;
 }
 
-/* Set up a tuntap device. */
-int setup_tun(struct openconnect_info *vpninfo)
+int openconnect_setup_tun_fd(struct openconnect_info *vpninfo, int tun_fd)
 {
-	int tun_fd;
+	fcntl(tun_fd, F_SETFD, FD_CLOEXEC);
 
-	set_script_env(vpninfo);
+	if (vpninfo->tun_fd != -1)
+		FD_CLR(vpninfo->tun_fd, &vpninfo->select_rfds);
+	vpninfo->tun_fd = tun_fd;
 
-	if (vpninfo->script_tun) {
-		pid_t child;
-		int fds[2];
+	if (vpninfo->select_nfds <= tun_fd)
+		vpninfo->select_nfds = tun_fd + 1;
 
-		if (socketpair(AF_UNIX, SOCK_DGRAM, 0, fds)) {
-			perror(_("socketpair"));
-			exit(1);
-		}
-		tun_fd = fds[0];
-		child = fork();
-		if (child < 0) {
-			perror(_("fork"));
-			exit(1);
-		} else if (!child) {
-			if (setpgid(0, getpid()) < 0)
-				perror(_("setpgid"));
-			close(tun_fd);
-			setenv_int("VPNFD", fds[1]);
-			execl("/bin/sh", "/bin/sh", "-c", vpninfo->vpnc_script, NULL);
-			perror(_("execl"));
-			exit(1);
-		}
-		close(fds[1]);
-		vpninfo->script_tun = child;
-		vpninfo->ifname = strdup(_("(script)"));
-	} else {
-		script_config_tun(vpninfo, "pre-init");
+	FD_SET(tun_fd, &vpninfo->select_rfds);
 
-		tun_fd = os_setup_tun(vpninfo);
-		if (tun_fd < 0)
-			return tun_fd;
+	fcntl(vpninfo->tun_fd, F_SETFL, fcntl(vpninfo->tun_fd, F_GETFL) | O_NONBLOCK);
 
-		setenv("TUNDEV", vpninfo->ifname, 1);
-		script_config_tun(vpninfo, "connect");
+	return 0;
+}
+
+int openconnect_setup_tun_script(struct openconnect_info *vpninfo, char *tun_script)
+{
+	pid_t child;
+	int fds[2];
 
-		/* Ancient vpnc-scripts might not get this right */
-		set_tun_mtu(vpninfo);
+	vpninfo->vpnc_script = tun_script;
+	vpninfo->script_tun = 1;
+
+	set_script_env(vpninfo);
+	if (socketpair(AF_UNIX, SOCK_DGRAM, 0, fds)) {
+		perror(_("socketpair"));
+		exit(1);
+	}
+	child = fork();
+	if (child < 0) {
+		perror(_("fork"));
+		exit(1);
+	} else if (!child) {
+		if (setpgid(0, getpid()) < 0)
+			perror(_("setpgid"));
+		close(fds[0]);
+		setenv_int("VPNFD", fds[1]);
+		execl("/bin/sh", "/bin/sh", "-c", vpninfo->vpnc_script, NULL);
+		perror(_("execl"));
+		exit(1);
 	}
+	close(fds[1]);
+	vpninfo->script_tun = child;
+	vpninfo->ifname = strdup(_("(script)"));
 
-	fcntl(tun_fd, F_SETFD, FD_CLOEXEC);
+	return openconnect_setup_tun_fd(vpninfo, fds[0]);
+}
 
-	vpninfo->tun_fd = tun_fd;
+int openconnect_setup_tun_device(struct openconnect_info *vpninfo, char *vpnc_script, char *ifname)
+{
+	int tun_fd;
 
-	if (vpninfo->select_nfds <= tun_fd)
-		vpninfo->select_nfds = tun_fd + 1;
+	vpninfo->vpnc_script = vpnc_script;
+	vpninfo->ifname = ifname;
 
-	FD_SET(tun_fd, &vpninfo->select_rfds);
+	set_script_env(vpninfo);
+	script_config_tun(vpninfo, "pre-init");
 
-	fcntl(vpninfo->tun_fd, F_SETFL, fcntl(vpninfo->tun_fd, F_GETFL) | O_NONBLOCK);
+	tun_fd = os_setup_tun(vpninfo);
+	if (tun_fd < 0)
+		return tun_fd;
 
-	return 0;
+	setenv("TUNDEV", vpninfo->ifname, 1);
+	script_config_tun(vpninfo, "connect");
+
+	/* Ancient vpnc-scripts might not get this right */
+	set_tun_mtu(vpninfo);
+
+	return openconnect_setup_tun_fd(vpninfo, tun_fd);
 }
 
 static struct pkt *out_pkt;
@@ -802,6 +816,7 @@ void shutdown_tun(struct openconnect_info *vpninfo)
 #endif
 	}
 
-	close(vpninfo->tun_fd);
+	if (vpninfo->vpnc_script)
+		close(vpninfo->tun_fd);
 	vpninfo->tun_fd = -1;
 }