一、背景
為了減少后臺應(yīng)用的系統(tǒng)資源消耗眷篇，提升用戶體驗忌警，Android 7.0（API 級別 24）對廣播施加了限制，Android 8.0（API 級別 26）讓這些限制更為嚴(yán)格里伯。
限制點(diǎn)：Android 8.0 +版本的應(yīng)用無法靜態(tài)注冊廣播接收者接收到隱式廣播。
基于android-13.0.0_r43 源碼測試：
| 廣播接收者 | 廣播發(fā)送方 | 結(jié)果 |
|---|---|---|
| 靜態(tài)注冊 | 隱式廣播 | ? |
| 靜態(tài)注冊 | 顯式廣播 | ? |
| 靜態(tài)注冊 | 隱式廣播 + addFlags(0x01000000)FLAG_RECEIVER_INCLUDE_BACKGROUND | ? |
| 靜態(tài)注冊 |
豁免的系統(tǒng)隱式廣播 測試：BOOT_COMPLETED 注：接收方需要添加權(quán)限：<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" /> |
? |
| 動態(tài)注冊 | 隱式/顯式廣播 | ? |
另外：需要簽名權(quán)限的廣播不受此限制所限，因為這些廣播只會發(fā)送到使用相同證書簽名的應(yīng)用再榄，而不是發(fā)送到設(shè)備上的所有應(yīng)用。
二享潜、限制點(diǎn)源碼分析
2.1 調(diào)試發(fā)送廣播方法梳理出核心調(diào)用棧：
at com.android.server.am.BroadcastQueue.performReceiveLocked(Native Method)
at com.android.server.am.BroadcastQueue.processNextBroadcastLocked(BroadcastQueue.java:1359)
at com.android.server.am.BroadcastQueue.processNextBroadcast(BroadcastQueue.java:1155)
at com.android.server.am.BroadcastQueue$BroadcastHandler.handleMessage(BroadcastQueue.java:224)
at com.android.server.am.BroadcastQueue.scheduleBroadcastsLocked(Native Method)
at com.android.server.am.ActivityManagerService.broadcastIntentLocked(ActivityManagerService.java:14208)
at com.android.server.am.ActivityManagerService.broadcastIntentWithFeature(ActivityManagerService.java:14461)
at android.app.ContextImpl.sendBroadcastAsUser(ContextImpl.java:1416)
2.2 核心限制點(diǎn)邏輯分析
Background execution not allowed: receiving Intent { act=android.intent.action.EVAN flg=0x10 } to com.stan.simpledemo/.TestReceiver
基于系統(tǒng)限制日志, 定位代碼：
com.android.server.am.BroadcastQueue#processNextBroadcastLocked(boolean fromMsg, boolean skipOomAdj)
...
// 靜態(tài)注冊的廣播接收者限制點(diǎn)
if (!skip) {
// ① AMS. getAppStartModeLOSP 返回的mode值
final int allowed = mService.getAppStartModeLOSP( 成mode
info.activityInfo.applicationInfo.uid, info.activityInfo.packageName,
info.activityInfo.applicationInfo.targetSdkVersion, -1, true, false, false);
if (allowed != ActivityManager.APP_START_MODE_NORMAL) {
// We won't allow this receiver to be launched if the app has been
// completely disabled from launches, or it was not explicitly sent
// to it and the app is in a state that should not receive it
// (depending on how getAppStartModeLOSP has determined that).
if (allowed == ActivityManager.APP_START_MODE_DISABLED) {
Slog.w(TAG, "Background execution disabled: receiving "
+ r.intent + " to "
+ component.flattenToShortString());
skip = true;
// ② intent參數(shù)判斷
} else if (((r.intent.getFlags()&Intent.FLAG_RECEIVER_EXCLUDE_BACKGROUND) != 0)
|| (r.intent.getComponent() == null
&& r.intent.getPackage() == null
&& ((r.intent.getFlags()
& Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND) == 0)
&& !isSignaturePerm(r.requiredPermissions))) {
mService.addBackgroundCheckViolationLocked(r.intent.getAction(),
component.getPackageName());
Slog.w(TAG, "Background execution not allowed: receiving "
+ r.intent + " to "
+ component.flattenToShortString());
skip = true;
}
}
}
...
這里主要有兩個部分：
- ① AMS. getAppStartModeLOSP 生成mode
- ② intent參數(shù)判斷
結(jié)合前面的測試困鸥，來看下是如何限制的：
① getAppStartModeLOSP 核心邏輯：
final int startMode = (alwaysRestrict) //當(dāng)前路徑下alwaysRestrict = true
? appRestrictedInBackgroundLOSP(uid, packageName, packageTargetSdk)
: appServicesRestrictedInBackgroundLOSP(uid, packageName,
packageTargetSdk);
而appRestrictedInBackgroundLOSP開頭就是版本限制：
int appRestrictedInBackgroundLOSP(int uid, String packageName, int packageTargetSdk) {
// Apps that target O+ are always subject to background check
if (packageTargetSdk >= Build.VERSION_CODES.O) {
if (DEBUG_BACKGROUND_CHECK) {
Slog.i(TAG, "App " + uid + "/" + packageName + " targets O+, restricted");
}
return ActivityManager.APP_START_MODE_DELAYED_RIGID;
}
...
從調(diào)試看，基本都是返回 2 即：APP_START_MODE_DELAYED_RIGID
② intent參數(shù)判斷
((r.intent.getFlags()&Intent.FLAG_RECEIVER_EXCLUDE_BACKGROUND) != 0)
|| (r.intent.getComponent() == null
&& r.intent.getPackage() == null
&& ((r.intent.getFlags()& Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND) == 0)
&& !isSignaturePerm(r.requiredPermissions))
二者滿足其一，廣播接收就會被限制疾就。
不限制條件總結(jié)：
首先澜术，intent不包含F(xiàn)LAG_RECEIVER_EXCLUDE_BACKGROUND，在此基礎(chǔ)上：
- 1）發(fā)送顯示廣播猬腰，即指定Component鸟废，r.intent.getComponent() == null 不滿足而繞過；
- 2）intent包含flag: Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND 即&上該flags不等于0繞過姑荷；
- 3）滿足組件簽名權(quán)限條件的盒延，可以繞過；
至此鼠冕，我們已經(jīng)知道了添寺，為什么發(fā)送顯示廣播、添加FLAG_RECEIVER_INCLUDE_BACKGROUND flag 懈费、滿足組件簽名權(quán)限條件可以繞過后臺廣播限制计露。
那么最后，豁免的系統(tǒng)隱式廣播是怎么繞過的呢? 還是BOOT_COMPLETED舉例分析：
com.android.server.am.UserController#sendLockedBootCompletedBroadcast
private void sendLockedBootCompletedBroadcast(IIntentReceiver receiver, @UserIdInt int userId) {
final Intent intent = new Intent(Intent.ACTION_LOCKED_BOOT_COMPLETED, null);
intent.putExtra(Intent.EXTRA_USER_HANDLE, userId);
intent.addFlags(Intent.FLAG_RECEIVER_NO_ABORT
| Intent.FLAG_RECEIVER_OFFLOAD
| Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND); // 添加了FLAG_RECEIVER_INCLUDE_BACKGROUND
mInjector.broadcastIntent(intent, null, receiver, 0, null, null,
new String[]{android.Manifest.permission.RECEIVE_BOOT_COMPLETED},
AppOpsManager.OP_NONE,
getTemporaryAppAllowlistBroadcastOptions(REASON_LOCKED_BOOT_COMPLETED)
.toBundle(), true,
false, MY_PID, SYSTEM_UID,
Binder.getCallingUid(), Binder.getCallingPid(), userId);
}
這里明顯看到構(gòu)建Intent的時候憎乙，添加了FLAG_RECEIVER_INCLUDE_BACKGROUND票罐。
2.3 廠商魔改分析
經(jīng)過測試，普通三方應(yīng)用靜態(tài)注冊的情況下泞边，基于原生系統(tǒng)顯式廣播/flag/豁免系統(tǒng)廣播方式均可拉活應(yīng)用胶坠，但是廠商（小米、華為繁堡、榮耀沈善、vivo、oppo）均無法拉活椭蹄， 主要是針對三方應(yīng)用非存活狀態(tài)下廣播接收做了限制闻牡。
以oppo（colorOs14 android 14）為例：
系統(tǒng)日志：
2024-10-24 17:08:54.652 1816-1877 OplusAppStartupManager system_server W prevent start com.stan.simpledemo, cmp ComponentInfo{com.stan.simpledemo/com.stan.simpledemo.TestReceiver} by broadcast com.stan.evan callingUid 10176, scenePriority = 0
定位到觸發(fā)的方法：com.android.server.am.OplusAppStartupManager#shouldPreventSendReceiverReal
限制關(guān)鍵方法：com.android.server.am.OplusAppStartupManager#isAllowForSPS
private SPSCase isAllowForSPS(Intent intent, int callingUid, String pkgName, String cpnName, int uid, String cpnType, ApplicationInfo appInfo) {
if (this.mOplusStartupStrategy.isInLruProcessesLocked(uid) && uid > 10000) {
return SPSCase.TRUE;
...
}
uid大于10000的應(yīng)用需要進(jìn)程存活情況下才不會被限制拉活。
其他廠商不做一一分析绳矩，這里僅貼下關(guān)鍵系統(tǒng)日志：
xiaomi:
10-24 16:35:34.018 2267 2311 W WakePathChecker: MIUILOG-AutoStart, Service/Provider/Broadcast Reject userId= 0 caller= com.stan.evan callee= com.stan.simpledemo classname=com.stan.simpledemo.TestReceiver action=android.intent.action.EVAN wakeType=2
10-24 16:35:34.018 2267 2311 W BroadcastQueueInjector: Unable to launch app com.stan.simpledemo/10181 for broadcast Intent { act=android.intent.action.EVAN flg=0x10 cmp=com.stan.simpledemo/.TestReceiver }: process is not permitted to wake path
vivo:
10-24 17:16:29.321 1486 1680 D _V_VivoBroadcastQueueModernImpl: intent:Intent { act=android.intent.action.EVAN flg=0x10 cmp=com.stan.simpledemo/.TestReceiver },toBeFiltered:true,userid:10325,packageName:com.stan.simpledemo
huawei/honor:
10-24 16:48:39.746 1692 3400 I ActivityManager: App 10040/com.stan.simpledemo targets O+, restricted
