Remove hardcoded DNS servers completely and improve DNS server setting

src/main/java/eu/siacs/conversations/ui/fragment/settings/ConnectionSettingsFragment.java

@@ -59,14 +59,14 @@ public class ConnectionSettingsFragment extends XmppPreferenceFragment {
 
                 final var dnsv4Server = (EditTextPreference) findPreference("dns_server_ipv4");
                 if (dnsv4Server != null) {
-                    dnsv4Server.setText("194.242.2.2");
+                    dnsv4Server.setText(null);
                 }
 
                 final var dnsv6Server = (EditTextPreference) findPreference("dns_server_ipv6");
                 if (dnsv6Server != null) {
-                    dnsv6Server.setText("[2a07:e340::2]");
+                    dnsv6Server.setText(null);
                 }
-
+                reconnectAccounts();
                 Toast.makeText(requireSettingsActivity(),R.string.dns_server_reset,Toast.LENGTH_LONG).show();
                 return true;
             });
@@ -105,7 +105,7 @@ public class ConnectionSettingsFragment extends XmppPreferenceFragment {
                 reconnectAccounts();
                 requireService().reinitializeMuclumbusService();
             }
-            case AppSettings.SHOW_CONNECTION_OPTIONS, AppSettings.PREFER_IPV6 -> {
+            case AppSettings.SHOW_CONNECTION_OPTIONS, AppSettings.PREFER_IPV6, "dns_server_ipv4", "dns_server_ipv6" -> {
                 reconnectAccounts();
             }
         }
@@ -146,4 +146,4 @@ public class ConnectionSettingsFragment extends XmppPreferenceFragment {
                         "%s is not %s",
                         activity.getClass().getName(), SettingsActivity.class.getName()));
     }
-}
+}

src/main/java/org/minidns/DnsClient.java

@@ -12,6 +12,11 @@ package org.minidns;
 
 import static org.webrtc.ApplicationContextProvider.getApplicationContext;
 
+import android.content.SharedPreferences;
+import android.text.TextUtils;
+
+import androidx.preference.PreferenceManager;
+
 import org.minidns.MiniDnsException.ErrorResponseException;
 import org.minidns.MiniDnsException.NoQueryPossibleException;
 import org.minidns.dnsmessage.DnsMessage;
@@ -23,7 +28,6 @@ import org.minidns.dnsserverlookup.AndroidUsingReflection;
 import org.minidns.dnsserverlookup.DnsServerLookupMechanism;
 import org.minidns.dnsserverlookup.UnixUsingEtcResolvConf;
 import org.minidns.record.Record.TYPE;
-import org.minidns.util.CollectionsUtil;
 import org.minidns.util.InetAddressUtil;
 import org.minidns.util.MultipleIoException;
 
@@ -39,11 +43,8 @@ import java.util.List;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
-import java.util.concurrent.CopyOnWriteArraySet;
 import java.util.logging.Level;
 
-import eu.siacs.conversations.R;
-
 /**
  * A minimal DNS client for SRV/A/AAAA/NS and CNAME lookups, with IDN support.
  * This circumvents the missing javax.naming package on android.
@@ -52,37 +53,20 @@ public class DnsClient extends AbstractDnsClient {
 
     static final List<DnsServerLookupMechanism> LOOKUP_MECHANISMS = new CopyOnWriteArrayList<>();
 
-    static final Set<Inet4Address> STATIC_IPV4_DNS_SERVERS = new CopyOnWriteArraySet<>();
-    static final Set<Inet6Address> STATIC_IPV6_DNS_SERVERS = new CopyOnWriteArraySet<>();
-
     static {
         addDnsServerLookupMechanism(AndroidUsingExec.INSTANCE);
         addDnsServerLookupMechanism(AndroidUsingReflection.INSTANCE);
         addDnsServerLookupMechanism(UnixUsingEtcResolvConf.INSTANCE);
-
-        try {
-            Inet4Address dnsforgeV4Dns = InetAddressUtil.ipv4From(eu.siacs.conversations.Conversations.getContext().getString(R.string.default_dns_server_ipv4));
-            STATIC_IPV4_DNS_SERVERS.add(dnsforgeV4Dns);
-        } catch (IllegalArgumentException e) {
-            LOGGER.log(Level.WARNING, "Could not add static IPv4 DNS Server", e);
-        }
-
-        try {
-            Inet6Address dnsforgeV6Dns = InetAddressUtil.ipv6From(eu.siacs.conversations.Conversations.getContext().getString(R.string.default_dns_server_ipv6));
-            STATIC_IPV6_DNS_SERVERS.add(dnsforgeV6Dns);
-        } catch (IllegalArgumentException e) {
-            LOGGER.log(Level.WARNING, "Could not add static IPv6 DNS Server", e);
-        }
     }
 
     private static final Set<String> blacklistedDnsServers = Collections.newSetFromMap(new ConcurrentHashMap<String, Boolean>(4));
 
     private final Set<InetAddress> nonRaServers = Collections.newSetFromMap(new ConcurrentHashMap<InetAddress, Boolean>(4));
 
-    private boolean askForDnssec = false;
+    private boolean askForDnssec = true;
     private boolean disableResultFilter = false;
 
-    private boolean useHardcodedDnsServers = true;
+    private boolean useHardcodedDnsServers = false;
 
     /**
      * Create a new DNS client using the global default cache.
@@ -103,36 +87,25 @@ public class DnsClient extends AbstractDnsClient {
     }
 
     private List<InetAddress> getServerAddresses() {
-        List<InetAddress> dnsServerAddresses = findDnsAddresses();
-
+        List<InetAddress> hardcodedDnsServers = new ArrayList<>();
         if (useHardcodedDnsServers) {
-            InetAddress primaryHardcodedDnsServer, secondaryHardcodedDnsServer = null;
-            switch (ipVersionSetting) {
-            case v4v6:
-                primaryHardcodedDnsServer = getRandomHardcodedIpv4DnsServer();
-                secondaryHardcodedDnsServer = getRandomHarcodedIpv6DnsServer();
-                break;
-            case v6v4:
-                primaryHardcodedDnsServer = getRandomHarcodedIpv6DnsServer();
-                secondaryHardcodedDnsServer = getRandomHardcodedIpv4DnsServer();
-                break;
-            case v4only:
-                primaryHardcodedDnsServer = getRandomHardcodedIpv4DnsServer();
-                break;
-            case v6only:
-                primaryHardcodedDnsServer = getRandomHarcodedIpv6DnsServer();
-                break;
-            default:
-                throw new AssertionError("Unknown ipVersionSetting: " + ipVersionSetting);
+            InetAddress primaryHardcodedDnsServer = getRandomHardcodedIpv4DnsServer();
+            if (primaryHardcodedDnsServer != null) {
+                hardcodedDnsServers.add(primaryHardcodedDnsServer);
             }
-
-            dnsServerAddresses.add(primaryHardcodedDnsServer);
+            InetAddress secondaryHardcodedDnsServer = getRandomHarcodedIpv6DnsServer();
             if (secondaryHardcodedDnsServer != null) {
-                dnsServerAddresses.add(secondaryHardcodedDnsServer);
+                hardcodedDnsServers.add(secondaryHardcodedDnsServer);
             }
         }
 
-        return dnsServerAddresses;
+        if (!hardcodedDnsServers.isEmpty()) {
+            // If custom servers are defined, use them exclusively.
+            return hardcodedDnsServers;
+        } else {
+            // Otherwise, fall back to the system's DNS servers.
+            return findDnsAddresses();
+        }
     }
 
     @Override
@@ -150,6 +123,10 @@ public class DnsClient extends AbstractDnsClient {
 
         List<InetAddress> dnsServerAddresses = getServerAddresses();
 
+        if (dnsServerAddresses.isEmpty()) {
+            throw new NoQueryPossibleException(q);
+        }
+
         List<IOException> ioExceptions = new ArrayList<>(dnsServerAddresses.size());
         for (InetAddress dns : dnsServerAddresses) {
             if (nonRaServers.contains(dns)) {
@@ -179,22 +156,22 @@ public class DnsClient extends AbstractDnsClient {
             }
 
             switch (responseMessage.responseCode) {
-            case NO_ERROR:
-            case NX_DOMAIN:
-                break;
-            default:
-                String warning = "Response from " + dns + " asked for " + q.getQuestion() + " with error code: "
-                        + responseMessage.responseCode + '.';
-                if (!LOGGER.isLoggable(Level.FINE)) {
-                    // Only append the responseMessage is log level is not fine. If it is fine or higher, the
-                    // response has already been logged.
-                    warning += "\n" + responseMessage;
-                }
-                LOGGER.warning(warning);
+                case NO_ERROR:
+                case NX_DOMAIN:
+                    break;
+                default:
+                    String warning = "Response from " + dns + " asked for " + q.getQuestion() + " with error code: "
+                            + responseMessage.responseCode + '.';
+                    if (!LOGGER.isLoggable(Level.FINE)) {
+                        // Only append the responseMessage is log level is not fine. If it is fine or higher, the
+                        // response has already been logged.
+                        warning += "\n" + responseMessage;
+                    }
+                    LOGGER.warning(warning);
 
-                ErrorResponseException exception = new ErrorResponseException(q, dnsQueryResult);
-                ioExceptions.add(exception);
-                continue;
+                    ErrorResponseException exception = new ErrorResponseException(q, dnsQueryResult);
+                    ioExceptions.add(exception);
+                    continue;
             }
 
             return dnsQueryResult;
@@ -259,7 +236,7 @@ public class DnsClient extends AbstractDnsClient {
             } catch (SecurityException exception) {
                 LOGGER.log(Level.WARNING, "Could not lookup DNS server", exception);
             }
-            if (res == null) {
+            if (res == null || res.isEmpty()) {
                 LOGGER.log(TRACE_LOG_LEVEL, "DnsServerLookupMechanism '" + mechanism.getName() + "' did not return any DNS server");
                 continue;
             }
@@ -279,15 +256,7 @@ public class DnsClient extends AbstractDnsClient {
                         new Object[] { mechanism.getName(), dnsServers });
             }
 
-            assert !res.isEmpty();
-
-            // We could cache if res only contains IP addresses and avoid the verification in case. Not sure if its really that beneficial
-            // though, because the list returned by the server mechanism is rather short.
-
-            // Verify the returned DNS servers: Ensure that only valid IP addresses are returned. We want to avoid that something else,
-            // especially a valid DNS name is returned, as this would cause the following String to InetAddress conversation using
-            // getByName(String) to cause a DNS lookup, which would be performed outside of the realm of MiniDNS and therefore also outside
-            // of its DNSSEC guarantees.
+            // Verify the returned DNS servers: Ensure that only valid IP addresses are returned.
             Iterator<String> it = res.iterator();
             while (it.hasNext()) {
                 String potentialDnsServer = it.next();
@@ -297,7 +266,7 @@ public class DnsClient extends AbstractDnsClient {
                     it.remove();
                 } else if (blacklistedDnsServers.contains(potentialDnsServer)) {
                     LOGGER.fine("The DNS server lookup mechanism '" + mechanism.getName()
-                    + "' returned a blacklisted result: '" + potentialDnsServer + "'");
+                            + "' returned a blacklisted result: '" + potentialDnsServer + "'");
                     it.remove();
                 }
             }
@@ -307,7 +276,7 @@ public class DnsClient extends AbstractDnsClient {
             }
 
             LOGGER.warning("The DNS server lookup mechanism '" + mechanism.getName()
-                        + "' returned not a single valid IP address after sanitazion");
+                    + "' returned not a single valid IP address after sanitazion");
             res = null;
         }
 
@@ -346,9 +315,7 @@ public class DnsClient extends AbstractDnsClient {
 
         int validServerAddresses = 0;
         for (String dnsServerString : res) {
-            // The following invariant must hold: "dnsServerString is a IP address". Therefore findDNS() must only return a List of Strings
-            // representing IP addresses. Otherwise the following call of getByName(String) may perform a DNS lookup without MiniDNS being
-            // involved. Something we want to avoid.
+            // The following invariant must hold: "dnsServerString is a IP address".
             assert InetAddressUtil.isIpAddress(dnsServerString);
 
             InetAddress dnsServerAddress;
@@ -380,20 +347,20 @@ public class DnsClient extends AbstractDnsClient {
         List<InetAddress> dnsServers = new ArrayList<>(validServerAddresses);
 
         switch (setting) {
-        case v4v6:
-            dnsServers.addAll(ipv4DnsServer);
-            dnsServers.addAll(ipv6DnsServer);
-            break;
-        case v6v4:
-            dnsServers.addAll(ipv6DnsServer);
-            dnsServers.addAll(ipv4DnsServer);
-            break;
-        case v4only:
-            dnsServers.addAll(ipv4DnsServer);
-            break;
-        case v6only:
-            dnsServers.addAll(ipv6DnsServer);
-            break;
+            case v4v6:
+                dnsServers.addAll(ipv4DnsServer);
+                dnsServers.addAll(ipv6DnsServer);
+                break;
+            case v6v4:
+                dnsServers.addAll(ipv6DnsServer);
+                dnsServers.addAll(ipv4DnsServer);
+                break;
+            case v4only:
+                dnsServers.addAll(ipv4DnsServer);
+                break;
+            case v6only:
+                dnsServers.addAll(ipv6DnsServer);
+                break;
         }
         return dnsServers;
     }
@@ -404,15 +371,10 @@ public class DnsClient extends AbstractDnsClient {
             return;
         }
         synchronized (LOOKUP_MECHANISMS) {
-            // We can't use Collections.sort(CopyOnWriteArrayList) with Java 7. So we first create a temp array, sort it, and replace
-            // LOOKUP_MECHANISMS with the result. For more information about the Java 7 Collections.sort(CopyOnWriteArarayList) issue see
-            // http://stackoverflow.com/a/34827492/194894
-            // TODO: Remove that workaround once MiniDNS is Java 8 only.
             ArrayList<DnsServerLookupMechanism> tempList = new ArrayList<>(LOOKUP_MECHANISMS.size() + 1);
             tempList.addAll(LOOKUP_MECHANISMS);
             tempList.add(dnsServerLookup);
 
-            // Sadly, this Collections.sort() does not with the CopyOnWriteArrayList on Java 7.
             Collections.sort(tempList);
 
             LOOKUP_MECHANISMS.clear();
@@ -459,11 +421,29 @@ public class DnsClient extends AbstractDnsClient {
     }
 
     public InetAddress getRandomHardcodedIpv4DnsServer() {
-        return CollectionsUtil.getRandomFrom(STATIC_IPV4_DNS_SERVERS, insecureRandom);
+        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
+        String dnsServer = preferences.getString("dns_server_ipv4", null);
+        if (TextUtils.isEmpty(dnsServer)) {
+            return null;
+        }
+        try {
+            return InetAddressUtil.ipv4From(dnsServer);
+        } catch (IllegalArgumentException e) {
+            return null;
+        }
     }
 
     public InetAddress getRandomHarcodedIpv6DnsServer() {
-        return CollectionsUtil.getRandomFrom(STATIC_IPV6_DNS_SERVERS, insecureRandom);
+        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
+        String dnsServer = preferences.getString("dns_server_ipv6", null);
+        if (TextUtils.isEmpty(dnsServer)) {
+            return null;
+        }
+        try {
+            return InetAddressUtil.ipv6From(dnsServer);
+        } catch (IllegalArgumentException e) {
+            return null;
+        }
     }
 
     private static Question getReverseIpLookupQuestionFor(DnsName dnsName) {
@@ -491,6 +471,6 @@ public class DnsClient extends AbstractDnsClient {
             throw new IllegalArgumentException("The provided inetAddress '" + inetAddress
                     + "' is neither of type Inet4Address nor Inet6Address");
         }
-     }
+    }
 
-}
+}

src/main/java/org/minidns/constants/DnsRootServer.java

@@ -12,7 +12,10 @@ package org.minidns.constants;
 
 import static org.webrtc.ApplicationContextProvider.getApplicationContext;
 
-import android.content.res.Resources;
+import android.content.SharedPreferences;
+import android.text.TextUtils;
+
+import androidx.preference.PreferenceManager;
 
 import org.minidns.util.InetAddressUtil;
 
@@ -46,9 +49,9 @@ public class DnsRootServer {
             rootServerInet4Address('k', 193,   0,  14, 129),
             rootServerInet4Address('l', 199,   7,  83,  42),
             rootServerInet4Address('m', 202,  12,  27,  33),
-        };
+    };
 
-        protected static final Inet6Address[] IPV6_ROOT_SERVERS = new Inet6Address[] {
+    protected static final Inet6Address[] IPV6_ROOT_SERVERS = new Inet6Address[] {
             rootServerInet6Address('a', 0x2001, 0x0503, 0xba3e, 0x0000, 0x0000, 0x000, 0x0002, 0x0030),
             rootServerInet6Address('b', 0x2001, 0x0500, 0x0084, 0x0000, 0x0000, 0x000, 0x0000, 0x000b),
             rootServerInet6Address('c', 0x2001, 0x0500, 0x0002, 0x0000, 0x0000, 0x000, 0x0000, 0x000c),
@@ -59,65 +62,75 @@ public class DnsRootServer {
             rootServerInet6Address('j', 0x2001, 0x0503, 0x0c27, 0x0000, 0x0000, 0x000, 0x0002, 0x0030),
             rootServerInet6Address('l', 0x2001, 0x0500, 0x0003, 0x0000, 0x0000, 0x000, 0x0000, 0x0042),
             rootServerInet6Address('m', 0x2001, 0x0dc3, 0x0000, 0x0000, 0x0000, 0x000, 0x0000, 0x0035),
-        };
+    };
 
-        private static Inet4Address rootServerInet4Address(char rootServerId, int addr0, int addr1, int addr2, int addr3) {
-            Inet4Address inetAddress;
-            String name = rootServerId + ".root-servers.net";
-                try {
-                    inetAddress = (Inet4Address) InetAddress.getByAddress(name, new byte[] { (byte) addr0, (byte) addr1, (byte) addr2,
-                            (byte) addr3 });
-                    IPV4_ROOT_SERVER_MAP.put(rootServerId, inetAddress);
-                } catch (UnknownHostException e) {
-                    // This should never happen, if it does it's our fault!
-                    throw new RuntimeException(e);
-                }
-
-            return inetAddress;
+    private static Inet4Address rootServerInet4Address(char rootServerId, int addr0, int addr1, int addr2, int addr3) {
+        Inet4Address inetAddress;
+        String name = rootServerId + ".root-servers.net";
+        try {
+            inetAddress = (Inet4Address) InetAddress.getByAddress(name, new byte[] { (byte) addr0, (byte) addr1, (byte) addr2,
+                    (byte) addr3 });
+            IPV4_ROOT_SERVER_MAP.put(rootServerId, inetAddress);
+        } catch (UnknownHostException e) {
+            // This should never happen, if it does it's our fault!
+            throw new RuntimeException(e);
         }
 
-        private static Inet6Address rootServerInet6Address(char rootServerId, int addr0, int addr1, int addr2, int addr3, int addr4, int addr5, int addr6, int addr7) {
-            Inet6Address inetAddress;
-            String name = rootServerId + ".root-servers.net";
-                try {
-                    inetAddress = (Inet6Address) InetAddress.getByAddress(name, new byte[] {
-                            // @formatter:off
-                            (byte) (addr0 >> 8), (byte) addr0, (byte) (addr1 >> 8), (byte) addr1,
-                            (byte) (addr2 >> 8), (byte) addr2, (byte) (addr3 >> 8), (byte) addr3,
-                            (byte) (addr4 >> 8), (byte) addr4, (byte) (addr5 >> 8), (byte) addr5,
-                            (byte) (addr6 >> 8), (byte) addr6, (byte) (addr7 >> 8), (byte) addr7
-                            // @formatter:on
-                    });
-                    IPV6_ROOT_SERVER_MAP.put(rootServerId, inetAddress);
-                } catch (UnknownHostException e) {
-                    // This should never happen, if it does it's our fault!
-                    throw new RuntimeException(e);
-                }
-            return inetAddress;
-        }
+        return inetAddress;
+    }
 
-        public static Inet4Address getRandomIpv4RootServer(Random random) {
-            if (getApplicationContext().getString(R.string.default_dns_server_ipv4).equals("194.242.2.2")) {
-                return IPV4_ROOT_SERVERS[random.nextInt(IPV4_ROOT_SERVERS.length)];
-            } else {
-                return InetAddressUtil.ipv4From(eu.siacs.conversations.Conversations.getContext().getString(R.string.default_dns_server_ipv4));
+    private static Inet6Address rootServerInet6Address(char rootServerId, int addr0, int addr1, int addr2, int addr3, int addr4, int addr5, int addr6, int addr7) {
+        Inet6Address inetAddress;
+        String name = rootServerId + ".root-servers.net";
+        try {
+            inetAddress = (Inet6Address) InetAddress.getByAddress(name, new byte[] {
+                    // @formatter:off
+                    (byte) (addr0 >> 8), (byte) addr0, (byte) (addr1 >> 8), (byte) addr1,
+                    (byte) (addr2 >> 8), (byte) addr2, (byte) (addr3 >> 8), (byte) addr3,
+                    (byte) (addr4 >> 8), (byte) addr4, (byte) (addr5 >> 8), (byte) addr5,
+                    (byte) (addr6 >> 8), (byte) addr6, (byte) (addr7 >> 8), (byte) addr7
+                    // @formatter:on
+            });
+            IPV6_ROOT_SERVER_MAP.put(rootServerId, inetAddress);
+        } catch (UnknownHostException e) {
+            // This should never happen, if it does it's our fault!
+            throw new RuntimeException(e);
+        }
+        return inetAddress;
+    }
+
+    public static Inet4Address getRandomIpv4RootServer(Random random) {
+        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
+        String dnsServer = preferences.getString("dns_server_ipv4", null);
+        if (!TextUtils.isEmpty(dnsServer)) {
+            try {
+                return InetAddressUtil.ipv4From(dnsServer);
+            } catch (IllegalArgumentException e) {
+                // Invalid format, do not fall back to root servers
             }
         }
+        return null;
+    }
 
-        public static Inet6Address getRandomIpv6RootServer(Random random) {
-            if (getApplicationContext().getString(R.string.default_dns_server_ipv6).equals("[2a07:e340::2]")) {
-                return IPV6_ROOT_SERVERS[random.nextInt(IPV6_ROOT_SERVERS.length)];
-            } else {
-                return InetAddressUtil.ipv6From(eu.siacs.conversations.Conversations.getContext().getString(R.string.default_dns_server_ipv6));
+    public static Inet6Address getRandomIpv6RootServer(Random random) {
+        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
+        String dnsServer = preferences.getString("dns_server_ipv6", null);
+        if (!TextUtils.isEmpty(dnsServer)) {
+            try {
+                return InetAddressUtil.ipv6From(dnsServer);
+            } catch (IllegalArgumentException e) {
+                // Invalid format, do not fall back to root servers
             }
         }
+        return null;
+    }
 
-        public static Inet4Address getIpv4RootServerById(char id) {
-            return IPV4_ROOT_SERVER_MAP.get(id);
-        }
+    public static Inet4Address getIpv4RootServerById(char id) {
+        return IPV4_ROOT_SERVER_MAP.get(id);
+    }
 
-        public static Inet6Address getIpv6RootServerById(char id) {
-            return IPV6_ROOT_SERVER_MAP.get(id);
-        }
+    public static Inet6Address getIpv6RootServerById(char id) {
+        return IPV6_ROOT_SERVER_MAP.get(id);
+    }
 
-}
+}

src/main/res/values/defaults.xml

@@ -62,8 +62,8 @@
     <bool name="show_nav_bar">true</bool>
     <bool name="enforce_dane">false</bool>
     <string name="default_chat_requests">disable</string>
-    <string name="default_dns_server_ipv4">194.242.2.2</string>
-    <string name="default_dns_server_ipv6">[2a07:e340::2]</string>
+    <string name="default_dns_server_ipv4"></string>
+    <string name="default_dns_server_ipv6"></string>
     <bool name="default_custom_tab">true</bool>
     <integer name="automatic_backup">0</integer>
     <bool name="call_integration">true</bool>

src/main/res/values/strings.xml

@@ -1317,16 +1317,16 @@
     <string name="pref_showtextformatting_sum">Show text formatting toolbar in chat while keyboard is shown</string>
     <string name="pref_showtextformatting">Text formatting toolbar</string>
     <string name="pref_chat_requests">Hide chats in Chat Requests area</string>
-    <string name="pref_dns_server_ipv4_summary">Change the default privacy focused IPv4 DNS server (Mullvad). Empty the field to use the DNS server of your device or VPN</string>
+    <string name="pref_dns_server_ipv4_summary">Add a custom IPv4 DNS server. Empty the field to use the DNS server of your device or VPN</string>
     <string name="pref_dns_server_ipv4_title">IPv4 DNS server</string>
     <string name="pref_dns_server_ipv6_title">IPv6 DNS server</string>
-    <string name="pref_dns_server_ipv6_summary">Change the default privacy focused IPv6 DNS server (Mullvad). Empty the field to use the DNS server of your device or VPN</string>
+    <string name="pref_dns_server_ipv6_summary">Add a custom IPv6 DNS server. Empty the field to use the DNS server of your device or VPN</string>
     <string name="all_chats">All chats</string>
     <string name="unread_chats">Unread chats</string>
     <string name="direct_messages">Direct messages</string>
     <string name="channels">Channels</string>
     <string name="manage_account">Manage account</string>
-    <string name="pref_reset_dns_server_summary">Reset the default DNS servers to the privacy focused DNS provider Mullvad</string>
+    <string name="pref_reset_dns_server_summary">Reset the custom DNS servers to the Android systems DNS server</string>
     <string name="pref_reset_dns_server_title">Reset DNS</string>
     <string name="dns_server_reset">DNS reset</string>
     <string name="pref_category_settings">Settings</string>