commit d63c4f35de30777533ae38e4e64e9fb53e24947e
author markchien <markchien@google.com> Thu May 21 17:38:28 2020 +0800
committer markchien <markchien@google.com> Sun May 24 22:52:44 2020 +0800
tree 39d631aa22986fbf4d4ce8ece2d2d1f11dcce1be
parent 366eae572dae8c511752671c474b35915b1e3be4

Adjust TTL for ipv6 tethering

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

Tethering/src/android/net/ip/IpServer.java

diff --git a/Tethering/src/android/net/ip/IpServer.java b/Tethering/src/android/net/ip/IpServer.java
index de53787..659d344 100644
--- a/Tethering/src/android/net/ip/IpServer.java
+++ b/Tethering/src/android/net/ip/IpServer.java
@@ -738,7 +738,7 @@
     //
     // 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 @@
             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 @@
         }
     }
 
-    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 @@
                     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 @@
                     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: