StrictMode to detect untagged network traffic.

Network usage is tracked by the kernel at the UID level, which is
granular enough for normal apps, but large components (such as the
system server) are impossible to debug without adding additional
socket tagging to help identify subsystems within a UID.

To help ensure that system components tag all their network traffic,
this change offers a new StrictMode option to detect and report
untagged sockets.

Test: builds, boots, all common traffic tagged
Bug: 30943431, 30414041
Change-Id: I825c7941076054732264690247de2863342638e2

services/core/java/com/android/server/connectivity/NetworkDiagnostics.java

@@ -23,6 +23,7 @@ import android.net.LinkProperties;
 import android.net.Network;
 import android.net.NetworkUtils;
 import android.net.RouteInfo;
+import android.net.TrafficStats;
 import android.os.SystemClock;
 import android.system.ErrnoException;
 import android.system.Os;
@@ -381,7 +382,12 @@ public class NetworkDiagnostics {
         protected void setupSocket(
                 int sockType, int protocol, long writeTimeout, long readTimeout, int dstPort)
                 throws ErrnoException, IOException {
-            mFileDescriptor = Os.socket(mAddressFamily, sockType, protocol);
+            final int oldTag = TrafficStats.getAndSetThreadStatsTag(TrafficStats.TAG_SYSTEM_PROBE);
+            try {
+                mFileDescriptor = Os.socket(mAddressFamily, sockType, protocol);
+            } finally {
+                TrafficStats.setThreadStatsTag(oldTag);
+            }
             // Setting SNDTIMEO is purely for defensive purposes.
             Os.setsockoptTimeval(mFileDescriptor,
                     SOL_SOCKET, SO_SNDTIMEO, StructTimeval.fromMillis(writeTimeout));