Factor out and speed up permission-checking code

Use the caching permission check for dump to save IPC.

Cache getpid() to save kernel call for other permission checks.

The C runtime library getpid() can't cache due to a fork
race condition, but we know that mediaserver doesn't fork.

Don't construct String16 on the stack.

Change-Id: I6be6161dae5155d39ba6ed6228e7683e67be34ed

1 files changed, 55 insertions, 0 deletions

diff --git a/services/audioflinger/ServiceUtilities.cpp b/services/audioflinger/ServiceUtilities.cpp
new file mode 100644
index 0000000..6a58852
--- /dev/null
+++ b/services/audioflinger/ServiceUtilities.cpp
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <binder/IPCThreadState.h>
+#include <binder/IServiceManager.h>
+#include <binder/PermissionCache.h>
+#include "ServiceUtilities.h"
+
+namespace android {
+
+// This optimization assumes mediaserver process doesn't fork, which it doesn't
+const pid_t getpid_cached = getpid();
+
+bool recordingAllowed() {
+    if (getpid_cached == IPCThreadState::self()->getCallingPid()) return true;
+    static const String16 sRecordAudio("android.permission.RECORD_AUDIO");
+    // don't use PermissionCache; this is not a system permission
+    bool ok = checkCallingPermission(sRecordAudio);
+    if (!ok) ALOGE("Request requires android.permission.RECORD_AUDIO");
+    return ok;
+}
+
+bool settingsAllowed() {
+    if (getpid_cached == IPCThreadState::self()->getCallingPid()) return true;
+    static const String16 sAudioSettings("android.permission.MODIFY_AUDIO_SETTINGS");
+    // don't use PermissionCache; this is not a system permission
+    bool ok = checkCallingPermission(sAudioSettings);
+    if (!ok) ALOGE("Request requires android.permission.MODIFY_AUDIO_SETTINGS");
+    return ok;
+}
+
+bool dumpAllowed() {
+    // don't optimize for same pid, since mediaserver never dumps itself
+    static const String16 sDump("android.permission.DUMP");
+    // OK to use PermissionCache; this is a system permission
+    bool ok = PermissionCache::checkCallingPermission(sDump);
+    // convention is for caller to dump an error message to fd instead of logging here
+    //if (!ok) ALOGE("Request requires android.permission.DUMP");
+    return ok;
+}
+
+} // namespace android