Obtain the MTU from a socket to the destination
The MTU from the socket is a much easier way to get the
correct MTU to any given destination. In particular this
is important for CLAT which used to be wrong :
on my device, with a perfectly working GoogleGuest :
50: v4-wlan0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1472 qdisc pfifo_fast state UNKNOWN group default qlen 500
F ICMPv4 payloadLength{1472} dst{8.8.8.8} src{192.0.0.4:27}: FAILED: 0/15 (4811ms)
After this patch, the payload is correctly 1444.
Test: Manual on GoogleGuest
Manual on a network with a custom set MTU
Change-Id: I6cd2398572b3fe08f88832ab6d0aa715c118cd4f
diff --git a/service/src/com/android/server/connectivity/NetworkDiagnostics.java b/service/src/com/android/server/connectivity/NetworkDiagnostics.java
index a367d9d..e1e2585 100644
--- a/service/src/com/android/server/connectivity/NetworkDiagnostics.java
+++ b/service/src/com/android/server/connectivity/NetworkDiagnostics.java
@@ -24,9 +24,12 @@
import static com.android.net.module.util.NetworkStackConstants.IPV4_HEADER_MIN_LEN;
import static com.android.net.module.util.NetworkStackConstants.IPV6_HEADER_LEN;
import static com.android.net.module.util.NetworkStackConstants.IPV6_MIN_MTU;
+import static com.android.net.module.util.NetworkStackConstants.IPV6_MTU;
+import static com.android.net.module.util.NetworkStackConstants.IP_MTU;
import android.annotation.NonNull;
import android.annotation.Nullable;
+import android.annotation.TargetApi;
import android.net.InetAddresses;
import android.net.LinkAddress;
import android.net.LinkProperties;
@@ -35,6 +38,7 @@
import android.net.TrafficStats;
import android.net.shared.PrivateDnsConfig;
import android.net.util.NetworkConstants;
+import android.os.Build;
import android.os.SystemClock;
import android.system.ErrnoException;
import android.system.Os;
@@ -213,14 +217,10 @@
mLinkProperties.addDnsServer(TEST_DNS6);
}
- final int lpMtu = mLinkProperties.getMtu();
- final int mtu = lpMtu > 0 ? lpMtu : ETHER_MTU;
for (RouteInfo route : mLinkProperties.getRoutes()) {
if (route.getType() == RouteInfo.RTN_UNICAST && route.hasGateway()) {
- InetAddress gateway = route.getGateway();
- // Use mtu in the route if exists. Otherwise, use the one in the link property.
- final int routeMtu = route.getMtu();
- prepareIcmpMeasurements(gateway, (routeMtu > 0) ? routeMtu : mtu);
+ final InetAddress gateway = route.getGateway();
+ prepareIcmpMeasurements(gateway);
if (route.isIPv6Default()) {
prepareExplicitSourceIcmpMeasurements(gateway);
}
@@ -228,7 +228,7 @@
}
for (InetAddress nameserver : mLinkProperties.getDnsServers()) {
- prepareIcmpMeasurements(nameserver, mtu);
+ prepareIcmpMeasurements(nameserver);
prepareDnsMeasurement(nameserver);
// Unlike the DnsResolver which doesn't do certificate validation in opportunistic mode,
@@ -285,24 +285,29 @@
// calculation.
if (addr instanceof Inet6Address) {
return IPV6_HEADER_LEN + ICMP_HEADER_LEN;
+ } else {
+ return IPV4_HEADER_MIN_LEN + ICMP_HEADER_LEN;
}
} catch (UnknownHostException e) {
- Log.e(TAG, "Create InetAddress fail(" + target + "): " + e);
+ throw new AssertionError("Create InetAddress fail(" + target + ")", e);
}
-
- return IPV4_HEADER_MIN_LEN + ICMP_HEADER_LEN;
}
- private void prepareIcmpMeasurements(@NonNull InetAddress target, int targetNetworkMtu) {
+ private void prepareIcmpMeasurements(@NonNull InetAddress target) {
+ int mtu = getMtuForTarget(target);
+ // If getMtuForTarget fails, it doesn't matter what mtu is used because connect can't
+ // succeed anyway
+ if (mtu <= 0) mtu = mLinkProperties.getMtu();
+ if (mtu <= 0) mtu = ETHER_MTU;
// Test with different size payload ICMP.
// 1. Test with 0 payload.
addPayloadIcmpMeasurement(target, 0);
final int header = getHeaderLen(target);
// 2. Test with full size MTU.
- addPayloadIcmpMeasurement(target, targetNetworkMtu - header);
+ addPayloadIcmpMeasurement(target, mtu - header);
// 3. If v6, make another measurement with the full v6 min MTU, unless that's what
// was done above.
- if ((target instanceof Inet6Address) && (targetNetworkMtu != IPV6_MIN_MTU)) {
+ if ((target instanceof Inet6Address) && (mtu != IPV6_MIN_MTU)) {
addPayloadIcmpMeasurement(target, IPV6_MIN_MTU - header);
}
}
@@ -321,6 +326,35 @@
}
}
+ /**
+ * Open a socket to the target address and return the mtu from that socket
+ *
+ * If the MTU can't be obtained for some reason (e.g. the target is unreachable) this will
+ * return -1.
+ *
+ * @param target the destination address
+ * @return the mtu to that destination, or -1
+ */
+ // getsockoptInt is S+, but this service code and only installs on S, so it's safe to ignore
+ // the lint warnings by using @TargetApi.
+ @TargetApi(Build.VERSION_CODES.S)
+ private int getMtuForTarget(InetAddress target) {
+ final int family = target instanceof Inet4Address ? AF_INET : AF_INET6;
+ try {
+ final FileDescriptor socket = Os.socket(family, SOCK_DGRAM, 0);
+ mNetwork.bindSocket(socket);
+ Os.connect(socket, target, 0);
+ if (family == AF_INET) {
+ return Os.getsockoptInt(socket, IPPROTO_IP, IP_MTU);
+ } else {
+ return Os.getsockoptInt(socket, IPPROTO_IPV6, IPV6_MTU);
+ }
+ } catch (ErrnoException | IOException e) {
+ Log.e(TAG, "Can't get MTU for destination " + target, e);
+ return -1;
+ }
+ }
+
private void prepareExplicitSourceIcmpMeasurements(InetAddress target) {
for (LinkAddress l : mLinkProperties.getLinkAddresses()) {
InetAddress source = l.getAddress();