Last-ditch clamping of negative NetworkStats.

We've seen reports of negative values flowing through to attempt
being recorded, which will outright crash.  This change does one
last-ditch check to see if we're about to work with negative values,
reporting any trouble and clamping them to zero so we don't crash.

This gives us the data we need to continue investigating without
triggering runtime restarts in the field.

Bug: 80057433
Test: atest android.net.NetworkStatsTest
Change-Id: I8174391c6cf5dadc2c2c10a8d841ee07e1f7d934

core/java/android/net/NetworkStats.java

@@ -1100,6 +1100,8 @@ public class NetworkStats implements Parcelable {
     public interface NonMonotonicObserver<C> {
         public void foundNonMonotonic(
                 NetworkStats left, int leftIndex, NetworkStats right, int rightIndex, C cookie);
+        public void foundNonMonotonic(
+                NetworkStats stats, int statsIndex, C cookie);
     }
 
     /**

services/core/java/com/android/server/net/NetworkStatsRecorder.java

@@ -241,6 +241,20 @@ public class NetworkStatsRecorder {
         NetworkStats.Entry entry = null;
         for (int i = 0; i < delta.size(); i++) {
             entry = delta.getValues(i, entry);
+
+            // As a last-ditch sanity check, report any negative values and
+            // clamp them so recording below doesn't croak.
+            if (entry.isNegative()) {
+                if (mObserver != null) {
+                    mObserver.foundNonMonotonic(delta, i, mCookie);
+                }
+                entry.rxBytes = Math.max(entry.rxBytes, 0);
+                entry.rxPackets = Math.max(entry.rxPackets, 0);
+                entry.txBytes = Math.max(entry.txBytes, 0);
+                entry.txPackets = Math.max(entry.txPackets, 0);
+                entry.operations = Math.max(entry.operations, 0);
+            }
+
             final NetworkIdentitySet ident = ifaceIdent.get(entry.iface);
             if (ident == null) {
                 unknownIfaces.add(entry.iface);

services/core/java/com/android/server/net/NetworkStatsService.java

@@ -1713,7 +1713,7 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
         @Override
         public void foundNonMonotonic(NetworkStats left, int leftIndex, NetworkStats right,
                 int rightIndex, String cookie) {
-            Log.w(TAG, "found non-monotonic values; saving to dropbox");
+            Log.w(TAG, "Found non-monotonic values; saving to dropbox");
 
             // record error for debugging
             final StringBuilder builder = new StringBuilder();
@@ -1722,9 +1722,21 @@ public class NetworkStatsService extends INetworkStatsService.Stub {
             builder.append("left=").append(left).append('\n');
             builder.append("right=").append(right).append('\n');
 
-            final DropBoxManager dropBox = (DropBoxManager) mContext.getSystemService(
+            mContext.getSystemService(DropBoxManager.class).addText(TAG_NETSTATS_ERROR,
-                    Context.DROPBOX_SERVICE);
+                    builder.toString());
-            dropBox.addText(TAG_NETSTATS_ERROR, builder.toString());
+        }
+
+        @Override
+        public void foundNonMonotonic(
+                NetworkStats stats, int statsIndex, String cookie) {
+            Log.w(TAG, "Found non-monotonic values; saving to dropbox");
+
+            final StringBuilder builder = new StringBuilder();
+            builder.append("Found non-monotonic " + cookie + " values at [" + statsIndex + "]\n");
+            builder.append("stats=").append(stats).append('\n');
+
+            mContext.getSystemService(DropBoxManager.class).addText(TAG_NETSTATS_ERROR,
+                    builder.toString());
         }
     }