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Adjust TTL for ipv6 tethering

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If upstream is cellular, set the TTL in Router Advertisements to
"network-set TTL - 1" for carrier requirement. For other non-cellular
upstream, set TTL as "network-set TTL + 1" to preventing arbitrary
distinction between tethered and untethered traffic.

Bug: 154776299
Test: atest TetheringTests

Change-Id: I7f2696a642f96c6aafb5613b980bf5bcdd08bbda
This commit is contained in:
markchien
2020-05-21 17:38:28 +08:00
parent 366eae572d
commit d63c4f35de
4 changed files with 80 additions and 18 deletions
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13
Tethering/src/android/net/ip/IpServer.java
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@@ -738,7 +738,7 @@ public class IpServer extends StateMachine {
//
// TODO: Evaluate using a data structure than is more directly suited to
// communicating only the relevant information.
private void updateUpstreamIPv6LinkProperties(LinkProperties v6only) {
private void updateUpstreamIPv6LinkProperties(LinkProperties v6only, int ttlAdjustment) {
if (mRaDaemon == null) return;
// Avoid unnecessary work on spurious updates.
@@ -761,7 +761,7 @@ public class IpServer extends StateMachine {
params.mtu = mUsingBpfOffload ? v6only.getMtu() - 16 : v6only.getMtu();
params.hasDefaultRoute = v6only.hasIpv6DefaultRoute();
if (params.hasDefaultRoute) params.hopLimit = getHopLimit(upstreamIface);
if (params.hasDefaultRoute) params.hopLimit = getHopLimit(upstreamIface, ttlAdjustment);
for (LinkAddress linkAddr : v6only.getLinkAddresses()) {
if (linkAddr.getPrefixLength() != RFC7421_PREFIX_LENGTH) continue;
@@ -1052,12 +1052,11 @@ public class IpServer extends StateMachine {
}
}
private byte getHopLimit(String upstreamIface) {
private byte getHopLimit(String upstreamIface, int adjustTTL) {
try {
int upstreamHopLimit = Integer.parseUnsignedInt(
mNetd.getProcSysNet(INetd.IPV6, INetd.CONF, upstreamIface, "hop_limit"));
// Add one hop to account for this forwarding device
upstreamHopLimit++;
upstreamHopLimit = upstreamHopLimit + adjustTTL;
// Cap the hop limit to 255.
return (byte) Integer.min(upstreamHopLimit, 255);
} catch (Exception e) {
@@ -1145,7 +1144,7 @@ public class IpServer extends StateMachine {
transitionTo(mUnavailableState);
break;
case CMD_IPV6_TETHER_UPDATE:
updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
break;
default:
return NOT_HANDLED;
@@ -1209,7 +1208,7 @@ public class IpServer extends StateMachine {
if (DBG) Log.d(TAG, "Untethered (ifdown)" + mIfaceName);
break;
case CMD_IPV6_TETHER_UPDATE:
updateUpstreamIPv6LinkProperties((LinkProperties) message.obj);
updateUpstreamIPv6LinkProperties((LinkProperties) message.obj, message.arg1);
sendLinkProperties();
break;
case CMD_IP_FORWARDING_ENABLE_ERROR: