Add DHCP workaround

Thanks to petergunn666 for debugging this with me.

mobile/src/main/java/be/mygod/vpnhotspot/App.kt

@@ -18,7 +18,6 @@ import io.fabric.sdk.android.Fabric
 class App : Application() {
     companion object {
         const val KEY_OPERATING_CHANNEL = "service.repeater.oc"
-        private const val KEY_MASQUERADE = "service.masquerade"
 
         @SuppressLint("StaticFieldLeak")
         lateinit var app: App
@@ -50,7 +49,8 @@ class App : Application() {
         val result = pref.getString(KEY_OPERATING_CHANNEL, null)?.toIntOrNull() ?: 0
         return if (result in 1..165) result else 0
     }
-    val masquerade: Boolean get() = pref.getBoolean(KEY_MASQUERADE, true)
+    val masquerade: Boolean get() = pref.getBoolean("service.masquerade", true)
+    val dhcpWorkaround: Boolean get() = pref.getBoolean("service.dhcpWorkaround", false)
 
     val cleanRoutings = Event0()
 }

mobile/src/main/java/be/mygod/vpnhotspot/LocalOnlyInterfaceManager.kt

@@ -40,15 +40,18 @@ class LocalOnlyInterfaceManager(val downstream: String) : UpstreamMonitor.Callba
     private fun initRouting(upstream: String? = null, owner: InterfaceAddress? = null,
                             dns: List<InetAddress> = this.dns) {
         try {
-            val routing = Routing(upstream, downstream, owner)
-            this.routing = routing
             this.dns = dns
-            val strict = app.pref.getBoolean("service.repeater.strict", false)
+            this.routing = Routing(upstream, downstream, owner).apply {
-            if (strict && upstream == null) return  // in this case, nothing to be done
+                val strict = app.pref.getBoolean("service.repeater.strict", false)
-            routing.ipForward()                     // local only interfaces need not enable ip_forward
+                if (strict && upstream == null) return@apply    // in this case, nothing to be done
-                    .rule().forward(strict)
+                if (app.dhcpWorkaround) dhcpWorkaround()
-            if (app.masquerade) routing.masquerade(strict)
+                ipForward()                                     // local only interfaces need to enable ip_forward
-            if (!routing.dnsRedirect(dns).start()) SmartSnackbar.make(R.string.noisy_su_failure).show()
+                rule()
+                forward(strict)
+                if (app.masquerade) masquerade(strict)
+                dnsRedirect(dns)
+                if (!start()) SmartSnackbar.make(R.string.noisy_su_failure).show()
+            }
         } catch (e: SocketException) {
             SmartSnackbar.make(e.localizedMessage).show()
             Crashlytics.logException(e)

mobile/src/main/java/be/mygod/vpnhotspot/TetheringService.kt

@@ -47,14 +47,17 @@ class TetheringService : IpNeighbourMonitoringService(), UpstreamMonitor.Callbac
                 var failed = false
                 for ((downstream, value) in routings) if (value == null || value.upstream != upstream)
                     try {
-                        // system tethering already has working forwarding rules
+                        routings[downstream] = Routing(upstream, downstream).apply {
-                        // so it doesn't make sense to add additional forwarding rules
+                            if (app.dhcpWorkaround) dhcpWorkaround()
-                        val routing = Routing(upstream, downstream).rule().forward()
+                            // system tethering already has working forwarding rules
-                        if (app.masquerade) routing.masquerade()
+                            // so it doesn't make sense to add additional forwarding rules
-                        routing.dnsRedirect(dns)
+                            rule()
-                        if (app.pref.getBoolean("service.disableIpv6", false)) routing.disableIpv6()
+                            forward()
-                        routings[downstream] = routing
+                            if (app.masquerade) masquerade()
-                        if (!routing.start()) failed = true
+                            dnsRedirect(dns)
+                            if (app.pref.getBoolean("service.disableIpv6", false)) disableIpv6()
+                            if (!start()) failed = true
+                        }
                     } catch (e: SocketException) {
                         e.printStackTrace()
                         Crashlytics.logException(e)

mobile/src/main/java/be/mygod/vpnhotspot/net/Routing.kt

@@ -27,6 +27,7 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
                 "$IPTABLES -t nat -F vpnhotspot_masquerade",
                 "$IPTABLES -t nat -X vpnhotspot_masquerade",
                 "quiet while ip rule del priority 17900; do done",
+                "quiet while ip rule del iif lo uidrange 0-0 lookup local_network priority 11000; do done",
                 report = false)
     }
 
@@ -40,15 +41,13 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
     private val stopScript = LinkedList<String>()
     var started = false
 
-    fun ipForward(): Routing {
+    fun ipForward() {
         startScript.add("echo 1 >/proc/sys/net/ipv4/ip_forward")
-        return this
     }
 
-    fun disableIpv6(): Routing {
+    fun disableIpv6() {
         startScript.add("echo 1 >/proc/sys/net/ipv6/conf/$downstream/disable_ipv6")
         stopScript.add("echo 0 >/proc/sys/net/ipv6/conf/$downstream/disable_ipv6")
-        return this
     }
 
     /**
@@ -57,16 +56,15 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
      *
      * Source: https://android.googlesource.com/platform/system/netd/+/b9baf26/server/RouteController.cpp#65
      */
-    fun rule(): Routing {
+    fun rule() {
         if (upstream != null) {
             startScript.add("ip rule add from all iif $downstream lookup $upstream priority 17900")
             // by the time stopScript is called, table entry for upstream may already get removed
             stopScript.addFirst("ip rule del from all iif $downstream priority 17900")
         }
-        return this
     }
 
-    fun forward(strict: Boolean = true): Routing {
+    fun forward(strict: Boolean = true) {
         startScript.add("quiet $IPTABLES -N vpnhotspot_fwd 2>/dev/null")
         if (strict) {
             check(upstream != null)
@@ -84,10 +82,9 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
         }
         startScript.add("$IPTABLES -I FORWARD -j vpnhotspot_fwd")
         stopScript.addFirst("$IPTABLES -D FORWARD -j vpnhotspot_fwd")
-        return this
     }
 
-    fun masquerade(strict: Boolean = true): Routing {
+    fun masquerade(strict: Boolean = true) {
         val hostSubnet = "${hostAddress.address.hostAddress}/${hostAddress.networkPrefixLength}"
         startScript.add("quiet $IPTABLES -t nat -N vpnhotspot_masquerade 2>/dev/null")
         // note: specifying -i wouldn't work for POSTROUTING
@@ -101,10 +98,9 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
         }
         startScript.add("$IPTABLES -t nat -I POSTROUTING -j vpnhotspot_masquerade")
         stopScript.addFirst("$IPTABLES -t nat -D POSTROUTING -j vpnhotspot_masquerade")
-        return this
     }
 
-    fun dnsRedirect(dnses: List<InetAddress>): Routing {
+    fun dnsRedirect(dnses: List<InetAddress>) {
         val hostAddress = hostAddress.address.hostAddress
         val dns = dnses.firstOrNull { it is Inet4Address }?.hostAddress ?: app.pref.getString("service.dns", "8.8.8.8")
         debugLog("Routing", "Using $dns from ($dnses)")
@@ -112,7 +108,19 @@ class Routing(val upstream: String?, private val downstream: String, ownerAddres
         startScript.add("$IPTABLES -t nat -A PREROUTING -i $downstream -p udp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         stopScript.addFirst("$IPTABLES -t nat -D PREROUTING -i $downstream -p tcp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         stopScript.addFirst("$IPTABLES -t nat -D PREROUTING -i $downstream -p udp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
-        return this
+    }
+
+    /**
+     * Similarly, assuming RULE_PRIORITY_VPN_OUTPUT_TO_LOCAL = 11000.
+     * Normally this is used to forward packets from remote to local, but it works anyways. It just needs to be before
+     * RULE_PRIORITY_SECURE_VPN = 12000. It would be great if we can gain better understanding into why this is only
+     * needed on some of the devices but not others.
+     *
+     * Source: https://android.googlesource.com/platform/system/netd/+/b9baf26/server/RouteController.cpp#57
+     */
+    fun dhcpWorkaround() {
+        startScript.add("ip rule add iif lo uidrange 0-0 lookup local_network priority 11000")
+        stopScript.addFirst("ip rule del iif lo uidrange 0-0 lookup local_network priority 11000")
     }
 
     fun start(): Boolean {

mobile/src/main/res/drawable/ic_action_build.xml

@@ -0,0 +1,6 @@
+<vector android:autoMirrored="true" android:height="24dp"
+    android:viewportHeight="24.0" android:viewportWidth="24.0"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android"
+    android:tint="?attr/colorControlNormal">
+    <path android:fillColor="#FF000000" android:pathData="M22.7,19l-9.1,-9.1c0.9,-2.3 0.4,-5 -1.5,-6.9 -2,-2 -5,-2.4 -7.4,-1.3L9,6 6,9 1.6,4.7C0.4,7.1 0.9,10.1 2.9,12.1c1.9,1.9 4.6,2.4 6.9,1.5l9.1,9.1c0.4,0.4 1,0.4 1.4,0l2.3,-2.3c0.5,-0.4 0.5,-1.1 0.1,-1.4z"/>
+</vector>

mobile/src/main/res/values-zh-rCN/strings.xml

@@ -71,6 +71,8 @@
     <string name="settings_service_upstream_auto">自动检测系统 VPN</string>
     <string name="settings_service_clean">清理/重新应用路由规则</string>
     <string name="settings_service_clean_summary">将修改的设置应用到当前启用的服务上。也可用于修复偶尔会发生的竞态条件。</string>
+    <string name="settings_service_dhcp_workaround">尝试修复 DHCP</string>
+    <string name="settings_service_dhcp_workaround_summary">如果设备无法获取 IP 地址，尝试打开这个选项。</string>
     <string name="settings_misc">杂项</string>
     <string name="settings_misc_logcat">导出调试信息</string>
     <string name="settings_misc_logcat_summary">这种非常有用哇</string>

mobile/src/main/res/values/strings.xml

@@ -74,6 +74,8 @@
     <string name="settings_service_dns">Fallback DNS server[:port]</string>
     <string name="settings_service_upstream">Upstream network interface</string>
     <string name="settings_service_upstream_auto">Auto detect system VPN</string>
+    <string name="settings_service_dhcp_workaround">Enable DHCP workaround</string>
+    <string name="settings_service_dhcp_workaround_summary">Use this if clients cannot obtain IP addresses.</string>
     <string name="settings_service_clean">Clean/reapply routing rules</string>
     <string name="settings_service_clean_summary">Update changed settings to current active services. Can also fix rare
         race conditions.</string>

mobile/src/main/res/xml/pref_settings.xml

@@ -40,6 +40,11 @@
             android:summary="@string/settings_service_upstream_auto"
             android:hint="@string/settings_service_upstream_auto"
             android:singleLine="true"/>
+        <SwitchPreference
+            android:key="service.dhcpWorkaround"
+            android:icon="@drawable/ic_action_build"
+            android:title="@string/settings_service_dhcp_workaround"
+            android:summary="@string/settings_service_disable_ipv6_summary"/>
     </PreferenceCategory>
     <PreferenceCategory
         android:title="@string/settings_misc">