LineageOS/android_packages_modules_Connectivity
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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
This commit is contained in:
Maciej Żenczykowski
2023-07-26 10:26:27 +00:00
parent 868859d4ef
commit 9f94648b7f
2 changed files with 5 additions and 5 deletions
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4
service/src/com/android/server/connectivity/ClatCoordinator.java
View File

@@ -78,7 +78,7 @@ public class ClatCoordinator {
@VisibleForTesting @VisibleForTesting
static final int MTU_DELTA = 28; static final int MTU_DELTA = 28;
@VisibleForTesting @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. // This must match the interface prefix in clatd.c.
private static final String CLAT_PREFIX = "v4-"; private static final String CLAT_PREFIX = "v4-";
@@ -673,7 +673,7 @@ public class ClatCoordinator {
throw new IOException("Detect MTU on " + tunIface + " failed: " + e); throw new IOException("Detect MTU on " + tunIface + " failed: " + e);
} }
final int mtu = adjustMtu(detectedMtu); 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. // Config tun interface mtu, address and bring up.
try { try {

6
tests/unit/java/com/android/server/connectivity/ClatCoordinatorTest.java
View File

@@ -508,10 +508,10 @@ public class ClatCoordinatorTest {
// Expected mtu is that the detected mtu minus MTU_DELTA(28). // Expected mtu is that the detected mtu minus MTU_DELTA(28).
assertEquals(1372, ClatCoordinator.adjustMtu(1400)); assertEquals(1372, ClatCoordinator.adjustMtu(1400));
assertEquals(1472, ClatCoordinator.adjustMtu(ETHER_MTU)); 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). // Expected mtu is that CLAT_MAX_MTU(1528) minus MTU_DELTA(28).
assertEquals(65508, ClatCoordinator.adjustMtu(CLAT_MAX_MTU + 1 /* over maximum mtu */)); assertEquals(1500, ClatCoordinator.adjustMtu(CLAT_MAX_MTU + 1 /* over maximum mtu */));
} }
private void verifyDump(final ClatCoordinator coordinator, boolean clatStarted) { private void verifyDump(final ClatCoordinator coordinator, boolean clatStarted) {