Android ContentProvider调用报错"Bad call:..."及相关Binder权限问题分析

时间  2019-11-16
标签 android contentprovider 调用 报错 bad 相关 binder 权限 问题 分析 栏目 Android 繁體版
原文   原文链接

问题：

项目中有一下状况：进程A调用另外一进程的Ｂ ContentProvider,Ｂ在该这次query中须要在query另外一个 Ｃ ContentProvider:java

class BContentProvider extends ContentProvider {
        Context mContext;
        ...
        @Override
        public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
            ...
            try {
                // query C ContentProvider：
                Cursor cursor = mContext.getContentResolver().query(...);
                if (cursor != null) {
                    try {
                        //do something;
                    } finally {
                        cursor.close();
                    }
                }
                Cursor cursor = mContext.getContentResolver().query(...);
            ...
        ...
            }
        }
    }
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在这种状况下，系统抛出Exception以下：android

1-11 16:04:51.867  2633  3557 W AppOps  : Bad call: specified package com.providers.xxx under uid 10032 but it is really 10001
01-11 16:04:51.867  2633  3557 W AppOps  : java.lang.RuntimeException: here
01-11 16:04:51.867  2633  3557 W AppOps  : 	at com.android.server.AppOpsService.getOpsRawLocked(AppOpsService.java:1399)
01-11 16:04:51.867  2633  3557 W AppOps  : 	at com.android.server.AppOpsService.noteOperationUnchecked(AppOpsService.java:1115)
01-11 16:04:51.867  2633  3557 W AppOps  : 	at com.android.server.AppOpsService.noteProxyOperation(AppOpsService.java:1093)
01-11 16:04:51.867  2633  3557 W AppOps  : 	at com.android.internal.app.IAppOpsService$Stub.onTransact(IAppOpsService.java:157)
01-11 16:04:51.867  2633  3557 W AppOps  : 	at android.os.BinderInjector.onTransact(BinderInjector.java:30)
01-11 16:04:51.867  2633  3557 W AppOps  : 	at android.os.Binder.execTransact(Binder.java:569)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: Writing exception to parcel
01-11 16:04:51.868  4659  6791 E DatabaseUtils: java.lang.SecurityException: Proxy package com.providers.xxx from uid 10001 or calling package com.providers.xxx from uid 10032 not allowed to perform READ_PROVIDER_C
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.app.AppOpsManager.noteProxyOp(AppOpsManager.java:1834)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProvider.checkPermissionAndAppOp(ContentProvider.java:538)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProvider.enforceReadPermissionInner(ContentProvider.java:560)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProvider$Transport.enforceReadPermission(ContentProvider.java:483)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProvider$Transport.query(ContentProvider.java:212)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentResolver.query(ContentResolver.java:532)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentResolver.query(ContentResolver.java:473)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at com.android.providers.xxx.BDatabaseHelper.query(BDatabaseHelper.java:7238)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProvider$Transport.query(ContentProvider.java:239)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:112)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.os.BinderInjector.onTransact(BinderInjector.java:30)
01-11 16:04:51.868  4659  6791 E DatabaseUtils: 	at android.os.Binder.execTransact(Binder.java:569)
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分析：

因为错误log首先反应了没有C ContentProvider的权限，但检查A应用是有C的读写权限的。因此排除了A的权限问题。 继续分析： 经过log能够看到确实是ContentProvider在作权限检查时出错。经过log中对应的源码进行分析： 首先能够看到ContentProvider.query()的时候作了权限检查，注意，传入的enforceReadPermission()的callingPkg是调用方的包名，以上面为例，就是B的包名。git

ContentProvider.query():bash

@Override
        public Cursor query(String callingPkg, Uri uri, @Nullable String[] projection, @Nullable Bundle queryArgs, @Nullable ICancellationSignal cancellationSignal) {
            validateIncomingUri(uri);
            uri = maybeGetUriWithoutUserId(uri);
            if (enforceReadPermission(callingPkg, uri, null) != AppOpsManager.MODE_ALLOWED) {
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enforceReadPermission()调用了.checkPermissionAndAppOp()方法，ContentProvider.checkPermissionAndAppOp()调用了AppOpsManager.noteProxyOp()去作检查出了异常。app

AppOpsManager.noteProxyOp()：ide

public int noteProxyOp(int op, String proxiedPackageName) {
        int mode = noteProxyOpNoThrow(op, proxiedPackageName);
        if (mode == MODE_ERRORED) {
            throw new SecurityException("Proxy package " + mContext.getOpPackageName()
                    + " from uid " + Process.myUid() + " or calling package "
                    + proxiedPackageName + " from uid " + Binder.getCallingUid()
                    + " not allowed to perform " + sOpNames[op]);
        }
        return mode;
    }
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noteProxyOpNoThrow()又作了什么呢？ AppOpsManager.noteProxyOpNoThrow():ui

/** * Like {@link #noteProxyOp(int, String)} but instead * of throwing a {@link SecurityException} it returns {@link #MODE_ERRORED}. * @hide */
    public int noteProxyOpNoThrow(int op, String proxiedPackageName) {
        try {
            return mService.noteProxyOperation(op, mContext.getOpPackageName(),
                    Binder.getCallingUid(), proxiedPackageName);
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }
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可见noteProxyOpNoThrow()是经过binder调用到了AppOpsService.noteProxyOperation()方法，注意，这里传入的是AppOpsService.noteProxyOperation()的后两个参数为Binder.getCallingUid()和以前层层传入的调用方的包名，也就是上面例子的B的包名。this

下面，继续看binder另外一侧的AppOpsService.noteProxyOperation()方法,咱们结合log中AppOps的输出log：spa

AppOpsService.noteProxyOperation():线程

@Override
    public int noteProxyOperation(int code, String proxyPackageName, int proxiedUid, String proxiedPackageName) {
        verifyIncomingOp(code);
        final int proxyUid = Binder.getCallingUid();
        String resolveProxyPackageName = resolvePackageName(proxyUid, proxyPackageName);
        if (resolveProxyPackageName == null) {
            return AppOpsManager.MODE_IGNORED;
        }
        final int proxyMode = noteOperationUnchecked(code, proxyUid,
                resolveProxyPackageName, -1, null);
        if (proxyMode != AppOpsManager.MODE_ALLOWED || Binder.getCallingUid() == proxiedUid) {
            return proxyMode;
        }
        String resolveProxiedPackageName = resolvePackageName(proxiedUid, proxiedPackageName);
        if (resolveProxiedPackageName == null) {
            return AppOpsManager.MODE_IGNORED;
        }
        return noteOperationUnchecked(code, proxiedUid, resolveProxiedPackageName,
                proxyMode, resolveProxyPackageName);
    }
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AppOpsService.noteOperationUnchecked():

private int noteOperationUnchecked(int code, int uid, String packageName, int proxyUid, String proxyPackageName) {
        Op op = null;
        Op switchOp = null;
        int switchCode;
        int resultMode = AppOpsManager.MODE_ALLOWED;
        synchronized (this) {
            Ops ops = getOpsRawLocked(uid, packageName, true);
          ...
         }
    ...
}
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AppOpsService.getOpsRawLocked():

private Ops getOpsRawLocked(int uid, String packageName, boolean edit) {
        ...
        Ops ops = uidState.pkgOps.get(packageName);
        if (ops == null) {
            if (!edit) {
                return null;
            }
            boolean isPrivileged = false;
            // This is the first time we have seen this package name under this uid,
            // so let's make sure it is valid.
            if (uid != 0) {
                final long ident = Binder.clearCallingIdentity();
                try {
                    int pkgUid = -1;
                    try {
                        ApplicationInfo appInfo = ActivityThread.getPackageManager()
                                .getApplicationInfo(packageName,
                                        PackageManager.MATCH_DEBUG_TRIAGED_MISSING,
                                        UserHandle.getUserId(uid));
                        if (appInfo != null) {
                            pkgUid = appInfo.uid;
                            isPrivileged = (appInfo.privateFlags
                                    & ApplicationInfo.PRIVATE_FLAG_PRIVILEGED) != 0;
                        }
                        ...
                    }
                    ...
                    if (pkgUid != uid) {
                        // Oops! The package name is not valid for the uid they are calling
                        // under. Abort.
                        RuntimeException ex = new RuntimeException("here");
                        ex.fillInStackTrace();
                        Slog.w(TAG, "Bad call: specified package " + packageName
                                + " under uid " + uid + " but it is really " + pkgUid, ex);
                        return null;
                    }
                } finally {
                    Binder.restoreCallingIdentity(ident);
                }
            }
            ops = new Ops(packageName, uidState, isPrivileged);
            uidState.pkgOps.put(packageName, ops);
        }
        return ops;
    }
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这里主要的操做就是将传入的uid和包名进行判断：比对该包对应的uid和传入的uid比较，若是不一致就报错。错误信息和log中的一致：

Bad call: specified package com.providers.xxx under uid 10032 but it is really 10001
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上文提到了，这个包名是传入的ContentProvider的调用方的包名，也就是例子中的B的包名。而uid是在AppOpsManager中经过Binder.getCallingUid()得到的。log中显示，此uid并非B的uid，而是其上游调用者A的uid。 为何在C中调用Binder.getCallingUid()获得的是A进程的呢？我找到了袁辉辉大神的一片博客： Binder IPC的权限控制

“线程B经过Binder调用当前线程的某个组件：此时线程B是线程B某个组件的调用端，则mCallingUid和mCallingPid应该保存当前线程B的PID和UID，故须要调用clearCallingIdentity()方法完成这个功能。当线程B调用完某个组件，因为线程B仍然处于线程A的被调用端，所以mCallingUid和mCallingPid须要恢复成线程A的UID和PID，这是调用restoreCallingIdentity()便可完成。”

Binder的机制就是这么设计的，因此须要在B进行下一次Binder调用(也就是query ContentProvider)以前调用clearCallingIdentity()来将B的 PID和UID附给mCallingUid和mCallingPid。Binder调用结束后在restoreCallingIdentity()来将其恢复成其本来调用方的PID和UID。这样在C里就会用B的相关信息进行权限校验，在AppOpsService.getOpsRawLocked()，UID和包名都是B的，是一致的，就不会报错。

解决办法

其实上文也已经提到了，参考 Binder IPC的权限控制，在B进行Query先后分别调用clearCallingIdentity() //做用是清空远程调用端的uid和pid，用当前本地进程的uid和pid替代，这样在以后的调用方去进行权限校验时会以B的信息为主，不会出现包名和UID不一致的状况。 最后修改过的调用方式以下：

long token = Binder.clearCallingIdentity();
        try {
            Cursor cursor = mContext.getContentResolver().query(...);
            if (cursor != null) {
                try {
                    //do something;
                } finally {
                    cursor.close();
                }
            }
        } finally {
            Binder.restoreCallingIdentity(token);
        }
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总结：

  1. ContentProvider是用Binder实现的，查询的过程其实就是一次Binder调用，因此想深刻了解ContentProvider必定要会一些Binder相关的知识。

  2. ContentProvider在接受一次查询前会调用AppOpsManager(其会经过Binder再由AppOpsService完成)进行权限校验，其中会校验调用方的UID和包名是否一致，其相关功能可见文章： Android 权限管理 —— AppOps。

  3. Binder调用时候能够经过Binder.getCallingPid()和Binder.getCallingUid()来获取调用方的PID和UID，而若是A经过Binder调用B，B又Binder调用了C，那么在C中Binder.getCallingPid()和Binder.getCallingUid()获得的是A的PID和UID，这种状况下须要在B调用C的先后用Binder.clearCallingIdentity()和Binder.restoreCallingIdentity()使其带上B的PID和UID，从而在C中进行权限校验时候用B的信息进行校验，固然这也符合逻辑，B调用的C，应该B须要有相应权限。

  4. Binder.clearCallingIdentity()和Binder.restoreCallingIdentity()的实现原理 Binder IPC的权限控制也有介绍，是经过移位实现的。

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