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/*
* Copyright (C) 2018 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.
*/
package com.android.server.util;
import static android.os.Binder.getCallingPid;
import static android.os.Binder.getCallingUid;
import android.os.Process;
import android.os.UserHandle;
import java.util.concurrent.atomic.AtomicInteger;
/**
* Utility class to check calling permissions on the network stack.
*/
public final class PermissionUtil {
private static final AtomicInteger sSystemPid = new AtomicInteger(-1);
/**
* Check that the caller is allowed to communicate with the network stack.
* @throws SecurityException The caller is not allowed to communicate with the network stack.
*/
public static void enforceNetworkStackCallingPermission() {
final int caller = getCallingUid();
if (caller == Process.SYSTEM_UID) {
checkConsistentSystemPid();
return;
}
if (caller != Process.myUid() && // apps with NETWORK_STACK_UID
UserHandle.getAppId(caller) != Process.BLUETOOTH_UID) {
throw new SecurityException("Invalid caller: " + caller);
}
}
private static void checkConsistentSystemPid() {
// Apart from the system server process, no process with a system UID should try to
// communicate with the network stack. This is to ensure that the network stack does not
// need to maintain behavior for clients it was not designed to work with.
// Checking that all calls from a system UID originate from the same PID loosely enforces
// this restriction as if another system process calls the network stack first, the system
// server would lose access to the network stack and cause obvious failures. If the system
// server calls the network stack first, other clients would lose access as expected.
final int systemPid = getCallingPid();
if (sSystemPid.compareAndSet(-1, systemPid)) {
// sSystemPid was unset (-1): this was the first call
return;
}
if (sSystemPid.get() != systemPid) {
throw new SecurityException("Invalid PID for the system server, expected "
+ sSystemPid.get() + " but was called from " + systemPid);
}
}
/**
* Check that the caller is allowed to dump the network stack, e.g. dumpsys.
* @throws SecurityException The caller is not allowed to dump the network stack.
*/
public static void checkDumpPermission() {
final int caller = getCallingUid();
if (caller != Process.myUid() && caller != Process.SYSTEM_UID && caller != Process.ROOT_UID
&& caller != Process.SHELL_UID) {
throw new SecurityException("No dump permissions for caller: " + caller);
}
}
private PermissionUtil() {
throw new UnsupportedOperationException("This class is not to be instantiated");
}
}
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