android: Apply configured MTU

While it is stored as property of individual profiles it is really a
global setting because we currently don't support more than one
connection.

src/frontends/android/jni/libandroidbridge/backend/android_service.c

@@ -32,8 +32,6 @@
 
 typedef struct private_android_service_t private_android_service_t;
 
-#define TUN_DEFAULT_MTU 1400
-
 /**
  * private data of Android service
  */
@@ -69,6 +67,11 @@ struct private_android_service_t {
 	 */
 	int tunfd;
 
+	/**
+	 * MTU of TUN device
+	 */
+	int mtu;
+
 	/**
 	 * DNS proxy
 	 */
@@ -176,7 +179,7 @@ static job_requeue_t handle_plain(private_android_service_t *this)
 		return JOB_REQUEUE_DIRECT;
 	}
 
-	raw = chunk_alloc(TUN_DEFAULT_MTU);
+	raw = chunk_alloc(this->mtu);
 	len = read(tunfd, raw.ptr, raw.len);
 	if (len < 0)
 	{
@@ -294,7 +297,7 @@ static bool setup_tun_device(private_android_service_t *this,
 		return FALSE;
 	}
 	if (!add_routes(builder, child_sa) ||
-		!builder->set_mtu(builder, TUN_DEFAULT_MTU))
+		!builder->set_mtu(builder, this->mtu))
 	{
 		return FALSE;
 	}
@@ -827,6 +830,7 @@ android_service_t *android_service_create(android_creds_t *creds,
 		.settings = settings,
 		.creds = creds,
 		.tunfd = -1,
+		.mtu = settings->get_int(settings, "global.mtu", ANDROID_DEFAULT_MTU),
 	);
 	/* only allow queries for the VPN gateway */
 	this->dns_proxy->add_hostname(this->dns_proxy,

src/frontends/android/jni/libandroidbridge/charonservice.c

@@ -44,7 +44,6 @@
 #define ANDROID_RETRASNMIT_TRIES 3
 #define ANDROID_RETRANSMIT_TIMEOUT 2.0
 #define ANDROID_RETRANSMIT_BASE 1.4
-#define ANDROID_FRAGMENT_SIZE 1400
 
 typedef struct private_charonservice_t private_charonservice_t;
 
@@ -409,6 +408,14 @@ static void initiate(settings_t *settings)
 	lib->settings->set_str(lib->settings,
 						"charon.plugins.tnc-imc.preferred_language",
 						settings->get_str(settings, "global.language", "en"));
+	/* this is actually the size of the complete IKE/IP packet, so if the MTU
+	 * for the TUN devices has to be reduced to pass traffic the IKE packets
+	 * will be a bit smaller than necessary as there is no IPsec overhead like
+	 * for the tunneled traffic (but compensating that seems like overkill) */
+	lib->settings->set_int(lib->settings,
+						"charon.fragment_size",
+						settings->get_int(settings, "global.mtu",
+										  ANDROID_DEFAULT_MTU));
 
 	this->creds->clear(this->creds);
 	DESTROY_IF(this->service);
@@ -467,8 +474,6 @@ static void set_options(char *logfile)
 					"charon.retransmit_timeout", ANDROID_RETRANSMIT_TIMEOUT);
 	lib->settings->set_double(lib->settings,
 					"charon.retransmit_base", ANDROID_RETRANSMIT_BASE);
-	lib->settings->set_int(lib->settings,
-					"charon.fragment_size", ANDROID_FRAGMENT_SIZE);
 	lib->settings->set_bool(lib->settings,
 					"charon.initiator_only", TRUE);
 	lib->settings->set_bool(lib->settings,

src/frontends/android/jni/libandroidbridge/charonservice.h

@@ -44,6 +44,11 @@ typedef enum android_vpn_state_t android_vpn_state_t;
 typedef enum android_imc_state_t android_imc_state_t;
 typedef struct charonservice_t charonservice_t;
 
+/**
+ * Default value for the MTU of TUN device and the size of IKE fragments
+ */
+#define ANDROID_DEFAULT_MTU 1400
+
 /**
  * VPN status codes. As defined in CharonVpnService.java
  */

src/frontends/android/src/org/strongswan/android/logic/CharonVpnService.java

@@ -219,6 +219,7 @@ public class CharonVpnService extends VpnService implements Runnable
 							Log.i(TAG, "charon started");
 							SettingsWriter writer = new SettingsWriter();
 							writer.setValue("global.language", Locale.getDefault().getLanguage());
+							writer.setValue("global.mtu", mCurrentProfile.getMTU());
 							writer.setValue("connection.type", mCurrentProfile.getVpnType().getIdentifier());
 							writer.setValue("connection.server", mCurrentProfile.getGateway());
 							writer.setValue("connection.username", mCurrentProfile.getUsername());