From 04252031522382efb7bb56566898a69ea25739da Mon Sep 17 00:00:00 2001
From: Hansen Kurli <hkurli@google.com>
Date: Wed, 7 Dec 2022 11:21:49 +0000
Subject: [PATCH] Ensure MTU is set for new interfaces.

Setting the MTU for an interface should not be skipped when the
interface names are different. This occurs when a VPN network creates
a new interface with identical MTU.

Bug: 246398088
Test: atest ConnectivityServiceTest
Test: Manual test: Connect to VPN network and switch networks
Test: Confirm MTU of interface is set correctly with `adb shell ip addr`
Change-Id: I811a01feca2fb2130c57c6c924145314180434c5
---
 .../com/android/server/ConnectivityService.java | 17 +++++++++--------
 .../android/server/ConnectivityServiceTest.java |  3 +--
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/service/src/com/android/server/ConnectivityService.java b/service/src/com/android/server/ConnectivityService.java
index a44494cabd..80ec8ae206 100755
--- a/service/src/com/android/server/ConnectivityService.java
+++ b/service/src/com/android/server/ConnectivityService.java
@@ -3116,22 +3116,23 @@ public class ConnectivityService extends IConnectivityManager.Stub
     private void updateMtu(@NonNull LinkProperties newLp, @Nullable LinkProperties oldLp) {
         final String iface = newLp.getInterfaceName();
         final int mtu = newLp.getMtu();
-        if (oldLp == null && mtu == 0) {
+        if (mtu == 0) {
             // Silently ignore unset MTU value.
             return;
         }
-        if (oldLp != null && newLp.isIdenticalMtu(oldLp)) {
-            if (VDBG) log("identical MTU - not setting");
+        if (oldLp != null && newLp.isIdenticalMtu(oldLp)
+                && TextUtils.equals(oldLp.getInterfaceName(), iface)) {
+            if (VDBG) log("identical MTU and iface - not setting");
             return;
         }
-        if (!LinkProperties.isValidMtu(mtu, newLp.hasGlobalIpv6Address())) {
-            if (mtu != 0) loge("Unexpected mtu value: " + mtu + ", " + iface);
+        // Cannot set MTU without interface name
+        if (TextUtils.isEmpty(iface)) {
+            if (VDBG) log("Setting MTU size with null iface.");
             return;
         }
 
-        // Cannot set MTU without interface name
-        if (TextUtils.isEmpty(iface)) {
-            loge("Setting MTU size with null iface.");
+        if (!LinkProperties.isValidMtu(mtu, newLp.hasGlobalIpv6Address())) {
+            loge("Unexpected mtu value: " + mtu + ", " + iface);
             return;
         }
 
diff --git a/tests/unit/java/com/android/server/ConnectivityServiceTest.java b/tests/unit/java/com/android/server/ConnectivityServiceTest.java
index 16f7039ee6..3d6ee099c5 100755
--- a/tests/unit/java/com/android/server/ConnectivityServiceTest.java
+++ b/tests/unit/java/com/android/server/ConnectivityServiceTest.java
@@ -17155,7 +17155,6 @@ public class ConnectivityServiceTest {
         mWiFiNetworkAgent.sendLinkProperties(new LinkProperties(lp2));
 
         waitForIdle();
-        // TODO(b/246398088): the MTU should be set on the new interface.
-        verify(mMockNetd, never()).interfaceSetMtu(eq(ifaceName2), eq(mtu));
+        verify(mMockNetd).interfaceSetMtu(eq(ifaceName2), eq(mtu));
     }
 }