Allow user to turn off safe mode on Android 10 (Mar 2020 or newer)

Fixes #153. Basically, this "forward"-ports a workaround for Android 9- thanks to Jimmy Chen. As a consequence, #31 might reoccur if you turn off safe mode.
2020-04-22 12:21:14 +08:00
parent 0dbf4b3b64
commit 3ba9a322c2
12 changed files with 121 additions and 88 deletions
--- a/mobile/src/main/java/be/mygod/vpnhotspot/RepeaterService.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/RepeaterService.kt
@@ -1,6 +1,7 @@
 package be.mygod.vpnhotspot

 import android.annotation.SuppressLint
+import android.annotation.TargetApi
 import android.app.Service
 import android.content.Intent
 import android.content.SharedPreferences
@@ -24,11 +25,13 @@ import be.mygod.vpnhotspot.net.wifi.WifiP2pManagerHelper.requestPersistentGroupI
 import be.mygod.vpnhotspot.net.wifi.WifiP2pManagerHelper.setWifiP2pChannels
 import be.mygod.vpnhotspot.net.wifi.WifiP2pManagerHelper.startWps
 import be.mygod.vpnhotspot.net.wifi.configuration.channelToFrequency
+import be.mygod.vpnhotspot.room.macToString
 import be.mygod.vpnhotspot.util.*
 import be.mygod.vpnhotspot.widget.SmartSnackbar
 import kotlinx.coroutines.*
 import timber.log.Timber
 import java.lang.reflect.InvocationTargetException
+import java.net.NetworkInterface

 /**
 * Service for handling Wi-Fi P2P. `supported` must be checked before this service is started otherwise it would crash.
@@ -36,6 +39,9 @@ import java.lang.reflect.InvocationTargetException
 class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListener,
        SharedPreferences.OnSharedPreferenceChangeListener {
    companion object {
+        const val KEY_SAFE_MODE = "service.repeater.safeMode"
+        private const val KEY_LAST_MAC = "service.repeater.lastMac"
+
        private const val KEY_NETWORK_NAME = "service.repeater.networkName"
        private const val KEY_PASSPHRASE = "service.repeater.passphrase"
        private const val KEY_OPERATING_BAND = "service.repeater.band"
@@ -57,9 +63,19 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
            }
        }
        val supported get() = p2pManager != null
-        @Deprecated("Not initialized and no use at all since API 29")
        var persistentSupported = false

+        private val hasP2pValidateName by lazy {
+            val (y, m, _) = Build.VERSION.SECURITY_PATCH.split('-', limit = 3).map { it.toInt() }
+            y > 2020 || y == 2020 && m >= 3
+        }
+        val safeModeConfigurable get() = Build.VERSION.SDK_INT >= 29 && hasP2pValidateName
+        val safeMode get() = Build.VERSION.SDK_INT >= 29 &&
+                (!hasP2pValidateName || app.pref.getBoolean(KEY_SAFE_MODE, true))
+        var lastMac: String?
+            get() = app.pref.getString(KEY_LAST_MAC, null)
+            private set(value) = app.pref.edit { putString(KEY_LAST_MAC, value) }
+
        var networkName: String?
            get() = app.pref.getString(KEY_NETWORK_NAME, null)
            set(value) = app.pref.edit { putString(KEY_NETWORK_NAME, value) }
@@ -94,7 +110,6 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
                }
            }
        val groupChanged = StickyEvent1 { group }
-        @Deprecated("Not initialized and no use at all since API 29")
        var thisDevice: WifiP2pDevice? = null

        fun startWps(pin: String? = null) {
@@ -136,13 +151,11 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
                    intent.getParcelableExtra(WifiP2pManager.EXTRA_WIFI_P2P_GROUP))
        }
    }
-    @Deprecated("No longer used since API 29")
-    @Suppress("DEPRECATION")
    private val deviceListener = broadcastReceiver { _, intent ->
        when (intent.action) {
            WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION -> binder.thisDevice =
                    intent.getParcelableExtra(WifiP2pManager.EXTRA_WIFI_P2P_DEVICE)
-            WifiP2pManagerHelper.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION -> onPersistentGroupsChanged()
+            WifiP2pManagerHelper.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION -> if (!safeMode) onPersistentGroupsChanged()
        }
    }
    /**
@@ -174,17 +187,13 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
    override fun onCreate() {
        super.onCreate()
        onChannelDisconnected()
-        if (Build.VERSION.SDK_INT < 29) @Suppress("DEPRECATION") {
-            registerReceiver(deviceListener, intentFilter(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION,
-                    WifiP2pManagerHelper.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION))
-            app.pref.registerOnSharedPreferenceChangeListener(this)
-        }
+        registerReceiver(deviceListener, intentFilter(WifiP2pManager.WIFI_P2P_THIS_DEVICE_CHANGED_ACTION,
+                WifiP2pManagerHelper.WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION))
+        app.pref.registerOnSharedPreferenceChangeListener(this)
    }

    override fun onBind(intent: Intent) = binder

-    @Deprecated("No longer used since API 29")
-    @Suppress("DEPRECATION")
    private fun setOperatingChannel(oc: Int = operatingChannel) = try {
        val channel = channel
        if (channel == null) SmartSnackbar.make(R.string.repeater_failure_disconnected).show()
@@ -207,21 +216,17 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
        channel = null
        if (status != Status.DESTROYED) try {
            channel = p2pManager.initialize(this, Looper.getMainLooper(), this)
-            if (Build.VERSION.SDK_INT < 29) @Suppress("DEPRECATION") setOperatingChannel()
+            if (!safeMode) setOperatingChannel()
        } catch (e: RuntimeException) {
            Timber.w(e)
            handler.postDelayed(this::onChannelDisconnected, 1000)
        }
    }

-    @Deprecated("No longer used since API 29")
-    @Suppress("DEPRECATION")
    override fun onSharedPreferenceChanged(sharedPreferences: SharedPreferences?, key: String?) {
-        if (key == KEY_OPERATING_CHANNEL) setOperatingChannel()
+        if (!safeMode && key == KEY_OPERATING_CHANNEL) setOperatingChannel()
    }

-    @Deprecated("No longer used since API 29")
-    @Suppress("DEPRECATION")
    private fun onPersistentGroupsChanged() {
        val channel = channel ?: return
        val device = binder.thisDevice ?: return
@@ -300,43 +305,45 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
        val networkName = networkName
        val passphrase = passphrase
        try {
-            if (Build.VERSION.SDK_INT < 29 || networkName == null || passphrase == null) {
+            if (!safeMode || networkName == null || passphrase == null) {
                persistNextGroup = true
                p2pManager.createGroup(channel, listener)
-            } else p2pManager.createGroup(channel, WifiP2pConfig.Builder().apply {
-                setNetworkName(PLACEHOLDER_NETWORK_NAME)
-                setPassphrase(passphrase)
-                operatingChannel.let { oc ->
-                    if (oc == 0) setGroupOperatingBand(operatingBand)
-                    else setGroupOperatingFrequency(channelToFrequency(oc))
-                }
-            }.build().run {
-                useParcel { p ->
-                    p.writeParcelable(this, 0)
-                    val end = p.dataPosition()
-                    p.setDataPosition(0)
-                    val creator = p.readString()
-                    val deviceAddress = p.readString()
-                    val wps = p.readParcelable<WpsInfo>(javaClass.classLoader)
-                    val long = p.readLong()
-                    check(p.readString() == PLACEHOLDER_NETWORK_NAME)
-                    check(p.readString() == passphrase)
-                    val extrasLength = end - p.dataPosition()
-                    check(extrasLength and 3 == 0)  // parcel should be padded
-                    if (extrasLength != 4) Timber.w(Exception("Unexpected extrasLength $extrasLength"))
-                    val extras = (0 until extrasLength / 4).map { p.readInt() }
-                    p.setDataPosition(0)
-                    p.writeString(creator)
-                    p.writeString(deviceAddress)
-                    p.writeParcelable(wps, 0)
-                    p.writeLong(long)
-                    p.writeString(networkName)
-                    p.writeString(passphrase)
-                    extras.forEach(p::writeInt)
-                    p.setDataPosition(0)
-                    p.readParcelable<WifiP2pConfig>(javaClass.classLoader)
-                }
-            }, listener)
+            } else @TargetApi(29) {
+                p2pManager.createGroup(channel, WifiP2pConfig.Builder().apply {
+                    setNetworkName(PLACEHOLDER_NETWORK_NAME)
+                    setPassphrase(passphrase)
+                    operatingChannel.let { oc ->
+                        if (oc == 0) setGroupOperatingBand(operatingBand)
+                        else setGroupOperatingFrequency(channelToFrequency(oc))
+                    }
+                }.build().run {
+                    useParcel { p ->
+                        p.writeParcelable(this, 0)
+                        val end = p.dataPosition()
+                        p.setDataPosition(0)
+                        val creator = p.readString()
+                        val deviceAddress = p.readString()
+                        val wps = p.readParcelable<WpsInfo>(javaClass.classLoader)
+                        val long = p.readLong()
+                        check(p.readString() == PLACEHOLDER_NETWORK_NAME)
+                        check(p.readString() == passphrase)
+                        val extrasLength = end - p.dataPosition()
+                        check(extrasLength and 3 == 0)  // parcel should be padded
+                        if (extrasLength != 4) Timber.w(Exception("Unexpected extrasLength $extrasLength"))
+                        val extras = (0 until extrasLength / 4).map { p.readInt() }
+                        p.setDataPosition(0)
+                        p.writeString(creator)
+                        p.writeString(deviceAddress)
+                        p.writeParcelable(wps, 0)
+                        p.writeLong(long)
+                        p.writeString(networkName)
+                        p.writeString(passphrase)
+                        extras.forEach(p::writeInt)
+                        p.setDataPosition(0)
+                        p.readParcelable<WifiP2pConfig>(javaClass.classLoader)
+                    }
+                }, listener)
+            }
        } catch (e: SecurityException) {
            Timber.w(e)
            startFailure(e.readableMessage)
@@ -371,7 +378,11 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
            persistNextGroup = false
        }
        check(routingManager == null)
-        routingManager = RoutingManager.LocalOnly(this, group.`interface`!!).apply { start() }
+        routingManager = object : RoutingManager.LocalOnly(this, group.`interface`!!) {
+            override fun ifaceHandler(iface: NetworkInterface) {
+                iface.hardwareAddress?.asIterable()?.macToString()?.let { lastMac = it }
+            }
+        }.apply { start() }
        status = Status.ACTIVE
        showNotification(group)
    }
@@ -426,10 +437,8 @@ class RepeaterService : Service(), CoroutineScope, WifiP2pManager.ChannelListene
            cancel()
            dispatcher.close()
        }
-        if (Build.VERSION.SDK_INT < 29) @Suppress("DEPRECATION") {
-            app.pref.unregisterOnSharedPreferenceChangeListener(this)
-            unregisterReceiver(deviceListener)
-        }
+        app.pref.unregisterOnSharedPreferenceChangeListener(this)
+        unregisterReceiver(deviceListener)
        status = Status.DESTROYED
        if (Build.VERSION.SDK_INT >= 27) channel?.close()
        super.onDestroy()
--- a/mobile/src/main/java/be/mygod/vpnhotspot/RoutingManager.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/RoutingManager.kt
@@ -7,6 +7,7 @@ import be.mygod.vpnhotspot.net.Routing
 import be.mygod.vpnhotspot.net.wifi.WifiDoubleLock
 import be.mygod.vpnhotspot.widget.SmartSnackbar
 import timber.log.Timber
+import java.net.NetworkInterface

 abstract class RoutingManager(private val caller: Any, val downstream: String, private val isWifi: Boolean) {
    companion object {
@@ -42,7 +43,7 @@ abstract class RoutingManager(private val caller: Any, val downstream: String, p
    /**
     * Both repeater and local-only hotspot are Wi-Fi based.
     */
-    class LocalOnly(caller: Any, downstream: String) : RoutingManager(caller, downstream, true) {
+    open class LocalOnly(caller: Any, downstream: String) : RoutingManager(caller, downstream, true) {
        override fun Routing.configure() {
            ipForward() // local only interfaces need to enable ip_forward
            forward()
@@ -63,8 +64,10 @@ abstract class RoutingManager(private val caller: Any, val downstream: String, p
        else -> error("Double routing detected for $downstream from $caller != ${other.caller}")
    }

+    open fun ifaceHandler(iface: NetworkInterface) { }
+
    private fun initRouting() = try {
-        routing = Routing(caller, downstream).apply {
+        routing = Routing(caller, downstream, this::ifaceHandler).apply {
            try {
                configure()
            } catch (e: Exception) {
--- a/mobile/src/main/java/be/mygod/vpnhotspot/SettingsPreferenceFragment.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/SettingsPreferenceFragment.kt
@@ -74,6 +74,10 @@ class SettingsPreferenceFragment : PreferenceFragmentCompat() {
            }
            boot.isChecked = BootReceiver.enabled
        } else boot.parent!!.removePreference(boot)
+        if (!RepeaterService.supported || !RepeaterService.safeModeConfigurable) {
+            val safeMode = findPreference<Preference>(RepeaterService.KEY_SAFE_MODE)!!
+            safeMode.parent!!.removePreference(safeMode)
+        }
        findPreference<Preference>("service.clean")!!.setOnPreferenceClickListener {
            GlobalScope.launch { RoutingManager.clean() }
            true
--- a/mobile/src/main/java/be/mygod/vpnhotspot/manage/RepeaterManager.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/manage/RepeaterManager.kt
@@ -56,7 +56,7 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic

        val title: CharSequence @Bindable get() {
            if (Build.VERSION.SDK_INT >= 29) binder?.group?.frequency?.let {
-                return parent.getString(R.string.repeater_channel, it, frequencyToChannel(it))
+                if (it != 0) return parent.getString(R.string.repeater_channel, it, frequencyToChannel(it))
            }
            return parent.getString(R.string.title_repeater)
        }
@@ -120,8 +120,6 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
        }
    }

-    @Deprecated("No longer used since API 29")
-    @Suppress("DEPRECATION")
    class ConfigHolder : ViewModel() {
        var config: P2pSupplicantConfiguration? = null
    }
@@ -134,7 +132,6 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
    private val data = Data()
    internal var binder: RepeaterService.Binder? = null
    private var p2pInterface: String? = null
-    @Suppress("DEPRECATION")
    private val holder by parent.viewModels<ConfigHolder>()

    override fun bindTo(viewHolder: RecyclerView.ViewHolder) {
@@ -164,7 +161,7 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
    }

    val configuration: WifiConfiguration? get() {
-        if (Build.VERSION.SDK_INT >= 29) {
+        if (RepeaterService.safeMode) {
            val networkName = RepeaterService.networkName
            val passphrase = RepeaterService.passphrase
            if (networkName != null && passphrase != null) {
@@ -179,7 +176,7 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
                    apChannel = RepeaterService.operatingChannel
                }
            }
-        } else @Suppress("DEPRECATION") {
+        } else {
            val group = binder?.group
            if (group != null) try {
                val config = P2pSupplicantConfiguration(group, binder?.thisDevice?.deviceAddress)
@@ -199,7 +196,7 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
        return null
    }
    suspend fun updateConfiguration(config: WifiConfiguration) {
-        if (Build.VERSION.SDK_INT >= 29) {
+        if (RepeaterService.safeMode) {
            RepeaterService.networkName = config.SSID
            RepeaterService.passphrase = config.preSharedKey
            RepeaterService.operatingBand = when (config.apBand) {
@@ -208,7 +205,7 @@ class RepeaterManager(private val parent: TetheringFragment) : Manager(), Servic
                AP_BAND_5GHZ -> WifiP2pConfig.GROUP_OWNER_BAND_5GHZ
                else -> throw IllegalArgumentException("Unknown apBand")
            }
-        } else @Suppress("DEPRECATION") holder.config?.let { master ->
+        } else holder.config?.let { master ->
            if (binder?.group?.networkName != config.SSID || master.psk != config.preSharedKey) try {
                withContext(Dispatchers.Default) { master.update(config.SSID, config.preSharedKey) }
                binder!!.group = null
--- a/mobile/src/main/java/be/mygod/vpnhotspot/net/Routing.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/net/Routing.kt
@@ -25,7 +25,8 @@ import java.net.SocketException
 *
 * Once revert is called, this object no longer serves any purpose.
 */
-class Routing(private val caller: Any, private val downstream: String) : IpNeighbourMonitor.Callback {
+class Routing(private val caller: Any, private val downstream: String,
+              ifaceHandler: (NetworkInterface) -> Unit) : IpNeighbourMonitor.Callback {
    companion object {
        /**
         * Since Android 5.0, RULE_PRIORITY_TETHERING = 18000.
@@ -117,8 +118,9 @@ class Routing(private val caller: Any, private val downstream: String) : IpNeigh
    }

    private val hostAddress = try {
-        val addresses = NetworkInterface.getByName(downstream)!!.interfaceAddresses!!
-                .filter { it.address is Inet4Address }
+        val iface = NetworkInterface.getByName(downstream)!!
+        ifaceHandler(iface)
+        val addresses = iface.interfaceAddresses!!.filter { it.address is Inet4Address }
        if (addresses.size > 1) error("More than one addresses was found: $addresses")
        addresses.first()
    } catch (e: Exception) {
--- a/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiP2pManagerHelper.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/WifiP2pManagerHelper.kt
@@ -11,7 +11,6 @@ import java.lang.reflect.Proxy

 object WifiP2pManagerHelper {
    const val UNSUPPORTED = -2
-    @Deprecated("No longer used since API 29")
    const val WIFI_P2P_PERSISTENT_GROUPS_CHANGED_ACTION = "android.net.wifi.p2p.PERSISTENT_GROUPS_CHANGED"

    /**
@@ -24,7 +23,6 @@ object WifiP2pManagerHelper {
        WifiP2pManager::class.java.getDeclaredMethod("setWifiP2pChannels", WifiP2pManager.Channel::class.java,
                Int::class.java, Int::class.java, WifiP2pManager.ActionListener::class.java)
    }
-    @Deprecated("No longer used since API 29")
    fun WifiP2pManager.setWifiP2pChannels(c: WifiP2pManager.Channel, lc: Int, oc: Int,
                                          listener: WifiP2pManager.ActionListener) {
        try {
@@ -63,7 +61,6 @@ object WifiP2pManagerHelper {
        WifiP2pManager::class.java.getDeclaredMethod("deletePersistentGroup",
                WifiP2pManager.Channel::class.java, Int::class.java, WifiP2pManager.ActionListener::class.java)
    }
-    @Deprecated("No longer used since API 29")
    fun WifiP2pManager.deletePersistentGroup(c: WifiP2pManager.Channel, netId: Int,
                                             listener: WifiP2pManager.ActionListener) {
        try {
@@ -90,7 +87,6 @@ object WifiP2pManagerHelper {
     * @param c is the channel created at {@link #initialize}
     * @param listener for callback when persistent group info list is available. Can be null.
     */
-    @Deprecated("No longer used since API 29")
    fun WifiP2pManager.requestPersistentGroupInfo(c: WifiP2pManager.Channel,
                                                  listener: (Collection<WifiP2pGroup>) -> Unit) {
        val proxy = Proxy.newProxyInstance(interfacePersistentGroupInfoListener.classLoader,
@@ -115,6 +111,5 @@ object WifiP2pManagerHelper {
    private val getNetworkId by lazy @SuppressLint("DiscouragedPrivateApi") {
        WifiP2pGroup::class.java.getDeclaredMethod("getNetworkId")
    }
-    @Deprecated("No longer used since API 29")
    val WifiP2pGroup.netId get() = getNetworkId.invoke(this) as Int
 }
--- a/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/configuration/P2pSupplicantConfiguration.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/configuration/P2pSupplicantConfiguration.kt
@@ -13,7 +13,6 @@ import java.io.File
 *   https://android.googlesource.com/platform/external/wpa_supplicant_8/+/d2986c2/wpa_supplicant/config.c#488
 *   https://android.googlesource.com/platform/external/wpa_supplicant_8/+/6fa46df/wpa_supplicant/config_file.c#182
 */
-@Deprecated("No longer used since API 29")
 class P2pSupplicantConfiguration(private val group: WifiP2pGroup, ownerAddress: String?) {
    companion object {
        private const val TAG = "P2pSupplicantConfiguration"
@@ -29,7 +28,7 @@ class P2pSupplicantConfiguration(private val group: WifiP2pGroup, ownerAddress:
        var pskLine: Int? = null
        var psk: String? = null
        var groupOwner = false
-        var bssidMatches = false
+        var bssid: String? = null

        override fun toString() = joinToString("\n")
    }
@@ -53,9 +52,9 @@ class P2pSupplicantConfiguration(private val group: WifiP2pGroup, ownerAddress:
            RootSession.checkOutput(command, shell, false, false)
            val parser = Parser(shell.out)
            try {
-                val bssids = listOfNotNull(group.owner.deviceAddress, ownerAddress)
+                val bssids = listOfNotNull(group.owner.deviceAddress, ownerAddress, RepeaterService.lastMac)
                        .distinct()
-                        .filter { it != "00:00:00:00:00:00" }
+                        .filter { it != "00:00:00:00:00:00" && it != "02:00:00:00:00:00" }
                while (parser.next()) {
                    if (parser.trimmed.startsWith("network={")) {
                        val block = NetworkBlock()
@@ -73,21 +72,20 @@ class P2pSupplicantConfiguration(private val group: WifiP2pGroup, ownerAddress:
                                            block.psk = match.groupValues[5].apply { check(length in 8..63) }
                                        }
                                        block.pskLine = block.size
-                                    } else if (bssids.any { matchedBssid.equals(it, true) }) block.bssidMatches = true
+                                    } else if (bssids.any { matchedBssid.equals(it, true) }) block.bssid = matchedBssid
                                }
                            }
                            block.add(parser.line)
                        }
                        block.add(parser.line)
                        result.add(block)
-                        if (block.bssidMatches && block.groupOwner && target == null) { // keep first only
+                        if (block.bssid != null && block.groupOwner && target == null) {    // keep first only
                            check(block.ssidLine != null && block.pskLine != null)
                            target = block
                        }
                    } else result.add(parser.line)
                }
                if (target == null && !RepeaterService.persistentSupported) {
-                    val bssid = bssids.single()
                    result.add("")
                    result.add(NetworkBlock().apply {
                        // generate a basic network block, it is likely that vendor is going to add more stuff here
--- a/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/configuration/WifiApDialogFragment.kt
+++ b/mobile/src/main/java/be/mygod/vpnhotspot/net/wifi/configuration/WifiApDialogFragment.kt
@@ -28,7 +28,6 @@ import be.mygod.vpnhotspot.util.toByteArray
 import be.mygod.vpnhotspot.util.toParcelable
 import be.mygod.vpnhotspot.widget.SmartSnackbar
 import kotlinx.android.parcel.Parcelize
-import java.nio.charset.Charset

 /**
 * Based on: https://android.googlesource.com/platform/packages/apps/Settings/+/39b4674/src/com/android/settings/wifi/WifiApDialog.java
@@ -117,7 +116,7 @@ class WifiApDialogFragment : AlertDialogFragment<WifiApDialogFragment.Arg, WifiA
            bandOptions = mutableListOf<BandOption>().apply {
                if (arg.p2pMode) {
                    add(BandOption.BandAny)
-                    if (Build.VERSION.SDK_INT >= 29) {
+                    if (RepeaterService.safeMode) {
                        add(BandOption.Band2GHz)
                        add(BandOption.Band5GHz)
                    }
@@ -160,8 +159,10 @@ class WifiApDialogFragment : AlertDialogFragment<WifiApDialogFragment.Arg, WifiA
     */
    private fun validate() {
        if (!started) return
-        val ssidValid = dialogView.ssid.length() != 0 &&
-                Charset.forName("UTF-8").encode(dialogView.ssid.text.toString()).limit() <= 32
+        val ssidLength = dialogView.ssid.text.toString().toByteArray().size
+        dialogView.ssidWrapper.error = if (RepeaterService.safeModeConfigurable && ssidLength < 9) {
+            requireContext().getString(R.string.settings_service_repeater_safe_mode_warning)
+        } else null
        val passwordValid = when (selectedSecurity) {
            WifiConfiguration.KeyMgmt.WPA_PSK, WPA2_PSK -> dialogView.password.length() >= 8
            else -> true    // do not try to validate
@@ -169,7 +170,8 @@ class WifiApDialogFragment : AlertDialogFragment<WifiApDialogFragment.Arg, WifiA
        dialogView.passwordWrapper.error = if (passwordValid) null else {
            requireContext().getString(R.string.credentials_password_too_short)
        }
-        (dialog as? AlertDialog)?.getButton(DialogInterface.BUTTON_POSITIVE)?.isEnabled = ssidValid && passwordValid
+        (dialog as? AlertDialog)?.getButton(DialogInterface.BUTTON_POSITIVE)?.isEnabled =
+                ssidLength in 1..32 && passwordValid
    }

    override fun onTextChanged(s: CharSequence, start: Int, before: Int, count: Int) { }
--- a/mobile/src/main/res/drawable/ic_alert_warning.xml
+++ b/mobile/src/main/res/drawable/ic_alert_warning.xml
@@ -0,0 +1,10 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24"
+    android:tint="?attr/colorControlNormal">
+  <path
+      android:fillColor="@android:color/white"
+      android:pathData="M1,21h22L12,2 1,21zM13,18h-2v-2h2v2zM13,14h-2v-4h2v4z"/>
+</vector>
--- a/mobile/src/main/res/values-zh-rCN/strings.xml
+++ b/mobile/src/main/res/values-zh-rCN/strings.xml
@@ -87,6 +87,9 @@
    <string name="settings_service_disable_ipv6">禁用 IPv6 共享</string>
    <string name="settings_service_disable_ipv6_summary">防止 VPN 通过 IPv6 泄漏。</string>
    <string name="settings_service_repeater_start_on_boot">开机自启动中继</string>
+    <string name="settings_service_repeater_safe_mode">中继安全模式</string>
+    <string name="settings_service_repeater_safe_mode_summary">不对系统配置进行修改，但是可能须要较长的网络名称。</string>
+    <string name="settings_service_repeater_safe_mode_warning">使用短名称可能需要关闭安全模式。</string>
    <string name="settings_service_wifi_lock">保持 Wi\u2011Fi 开启</string>
    <string name="settings_service_wifi_lock_none">系统默认</string>
    <string name="settings_service_wifi_lock_full">开</string>
--- a/mobile/src/main/res/values/strings.xml
+++ b/mobile/src/main/res/values/strings.xml
@@ -92,6 +92,10 @@
    <string name="settings_service_disable_ipv6">Disable IPv6 tethering</string>
    <string name="settings_service_disable_ipv6_summary">Enabling this option will prevent VPN leaks via IPv6.</string>
    <string name="settings_service_repeater_start_on_boot">Start repeater on boot</string>
+    <string name="settings_service_repeater_safe_mode">Repeater safe mode</string>
+    <string name="settings_service_repeater_safe_mode_summary">Makes no changes to your system configuration but might
+        not work with short SSIDs.</string>
+    <string name="settings_service_repeater_safe_mode_warning">Short SSIDs might require turning off safe mode.</string>
    <string name="settings_service_wifi_lock">Keep Wi\u2011Fi alive</string>
    <string name="settings_service_wifi_lock_none">System default</string>
    <string name="settings_service_wifi_lock_full">On</string>
--- a/mobile/src/main/res/xml/pref_settings.xml
+++ b/mobile/src/main/res/xml/pref_settings.xml
@@ -62,6 +62,12 @@
            app:key="service.repeater.startOnBoot"
            app:icon="@drawable/ic_action_autorenew"
            app:title="@string/settings_service_repeater_start_on_boot"/>
+        <SwitchPreference
+            app:key="service.repeater.safeMode"
+            app:icon="@drawable/ic_alert_warning"
+            app:title="@string/settings_service_repeater_safe_mode"
+            app:summary="@string/settings_service_repeater_safe_mode_summary"
+            app:defaultValue="true"/>
        <com.takisoft.preferencex.SimpleMenuPreference
            app:key="service.ipMonitor"
            app:icon="@drawable/ic_hardware_device_hub"