From 9f94648b7f04abeaaf34bd256f6d2ab74e210065 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Maciej=20=C5=BBenczykowski?= <maze@google.com>
Date: Wed, 26 Jul 2023 10:26:27 +0000
Subject: [PATCH] Lower CLAT max MTU from 65536 to 1528.
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Android's clat is for reaching the internet, which in general
never has an ipv4 L3 mtu higher than 1500.
(We could probably hit this on a jumboframe enabled IPv6-only
wifi network [ http://b/292057969#comment18 ] where RA claims
MTU of 9K [9170])
Bug: 292057969
Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I7a32455571458b8a3f1121ad980d54323b2ef06b
---
.../com/android/server/connectivity/ClatCoordinator.java | 4 ++--
.../android/server/connectivity/ClatCoordinatorTest.java | 6 +++---
2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/service/src/com/android/server/connectivity/ClatCoordinator.java b/service/src/com/android/server/connectivity/ClatCoordinator.java
index eb3e7cea7a..17de1461fb 100644
--- a/service/src/com/android/server/connectivity/ClatCoordinator.java
+++ b/service/src/com/android/server/connectivity/ClatCoordinator.java
@@ -78,7 +78,7 @@ public class ClatCoordinator {
@VisibleForTesting
static final int MTU_DELTA = 28;
@VisibleForTesting
- static final int CLAT_MAX_MTU = 65536;
+ static final int CLAT_MAX_MTU = 1500 + MTU_DELTA;
// This must match the interface prefix in clatd.c.
private static final String CLAT_PREFIX = "v4-";
@@ -673,7 +673,7 @@ public class ClatCoordinator {
throw new IOException("Detect MTU on " + tunIface + " failed: " + e);
}
final int mtu = adjustMtu(detectedMtu);
- Log.i(TAG, "ipv4 mtu is " + mtu);
+ Log.i(TAG, "detected ipv4 mtu of " + detectedMtu + " adjusted to " + mtu);
// Config tun interface mtu, address and bring up.
try {
diff --git a/tests/unit/java/com/android/server/connectivity/ClatCoordinatorTest.java b/tests/unit/java/com/android/server/connectivity/ClatCoordinatorTest.java
index 4158663999..88044be116 100644
--- a/tests/unit/java/com/android/server/connectivity/ClatCoordinatorTest.java
+++ b/tests/unit/java/com/android/server/connectivity/ClatCoordinatorTest.java
@@ -508,10 +508,10 @@ public class ClatCoordinatorTest {
// Expected mtu is that the detected mtu minus MTU_DELTA(28).
assertEquals(1372, ClatCoordinator.adjustMtu(1400));
assertEquals(1472, ClatCoordinator.adjustMtu(ETHER_MTU));
- assertEquals(65508, ClatCoordinator.adjustMtu(CLAT_MAX_MTU));
+ assertEquals(1500, ClatCoordinator.adjustMtu(CLAT_MAX_MTU));
- // Expected mtu is that CLAT_MAX_MTU(65536) minus MTU_DELTA(28).
- assertEquals(65508, ClatCoordinator.adjustMtu(CLAT_MAX_MTU + 1 /* over maximum mtu */));
+ // Expected mtu is that CLAT_MAX_MTU(1528) minus MTU_DELTA(28).
+ assertEquals(1500, ClatCoordinator.adjustMtu(CLAT_MAX_MTU + 1 /* over maximum mtu */));
}
private void verifyDump(final ClatCoordinator coordinator, boolean clatStarted) {
--
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