Emulator: handle OOM and Protocol error cases

- OutOfMemoryError can happen naturally if the size of the clipboard is
   too large to allocate. We should prefer to drop the clipboard data if
   we have a choice between that and crashing the system server.

 - OutOfMemoryError can happen unnatturally if the protocol gets out of
   sync with the host. This can happen quite easily if there is a caught
   exception and the clipboard monitor tries to keep on trucking, since
   the protocol doesn't have any built in synchronisation to catch back
   up to the start of the next message again. The only option to prevent
   that at the moment is to just close the pipe and reopen it in case
   of failure to understand something.

Bug: 231340598
Test: presubmit
Change-Id: Icceb8ec8b3988c32a2eb5f5598a43753460fc26b

services/core/java/com/android/server/clipboard/EmulatorClipboardMonitor.java

@@ -29,6 +29,7 @@ import android.util.Slog;
 import java.io.EOFException;
 import java.io.FileDescriptor;
 import java.io.InterruptedIOException;
+import java.net.ProtocolException;
 import java.net.SocketException;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
@@ -39,12 +40,16 @@ import java.util.function.Consumer;
 // write contents of the host system's clipboard.
 class EmulatorClipboardMonitor implements Consumer<ClipData> {
     private static final String TAG = "EmulatorClipboardMonitor";
+
     private static final String PIPE_NAME = "pipe:clipboard";
     private static final int HOST_PORT = 5000;
-    private final Thread mHostMonitorThread;
+
     private static final boolean LOG_CLIBOARD_ACCESS =
             SystemProperties.getBoolean("ro.boot.qemu.log_clipboard_access", false);
+    private static final int MAX_CLIPBOARD_BYTES = 128 << 20;
+
     private FileDescriptor mPipe = null;
+    private final Thread mHostMonitorThread;
 
     private static byte[] createOpenHandshake() {
         // String.getBytes doesn't include the null terminator,
@@ -97,8 +102,8 @@ class EmulatorClipboardMonitor implements Consumer<ClipData> {
         return fd;
     }
 
-    private static byte[] receiveMessage(final FileDescriptor fd) throws ErrnoException,
-            InterruptedIOException, EOFException {
+    private byte[] receiveMessage(final FileDescriptor fd) throws ErrnoException,
+            InterruptedIOException, EOFException, ProtocolException {
         final byte[] lengthBits = new byte[4];
         readFully(fd, lengthBits, 0, lengthBits.length);
 
@@ -106,6 +111,10 @@ class EmulatorClipboardMonitor implements Consumer<ClipData> {
         bb.order(ByteOrder.LITTLE_ENDIAN);
         final int msgLen = bb.getInt();
 
+        if (msgLen <= 0 || msgLen > MAX_CLIPBOARD_BYTES) {
+            throw new ProtocolException("Clipboard message length: " + msgLen + " out of bounds.");
+        }
+
         final byte[] msg = new byte[msgLen];
         readFully(fd, msg, 0, msg.length);
 
@@ -150,7 +159,8 @@ class EmulatorClipboardMonitor implements Consumer<ClipData> {
                     }
                     setAndroidClipboard.accept(clip);
                 } catch (ErrnoException | EOFException | InterruptedIOException
-                         | InterruptedException e) {
+                         | InterruptedException | ProtocolException | OutOfMemoryError e) {
+                    Slog.w(TAG, "Failure to read from host clipboard", e);
                     setPipeFD(null);
 
                     try {