Android的权限机制小结

Android的权限机制总结

 1     boolean checkCallingPermission(String permission, String func) { 2         // Quick check: if the calling permission is me, it's all okay. 3         if (Binder.getCallingPid() == Process.myPid()) { 4             return true; 5         } 6  7         if (mContext.checkCallingPermission(permission) 8                 == PackageManager.PERMISSION_GRANTED) { 9             return true;10         }11         String msg = "Permission Denial: " + func + " from pid="12                 + Binder.getCallingPid()13                 + ", uid=" + Binder.getCallingUid()14                 + " requires " + permission;15         Slog.w(TAG, msg);16         return false;17     }

上面函数返回false的时候抛出异常，那么返回true的时候就是权限检查通过了，继续跟进Context.java

 1     @Override 2     public int checkPermission(String permission, int pid, int uid) { 3         if (permission == null) { 4             throw new IllegalArgumentException("permission is null"); 5         } 6  7         if (!Process.supportsProcesses()) { 8             return PackageManager.PERMISSION_GRANTED; 9         }10         try {11             return ActivityManagerNative.getDefault().checkPermission(12                     permission, pid, uid);13         } catch (RemoteException e) {14             return PackageManager.PERMISSION_DENIED;15         }16     }17 18     @Override19     public int checkCallingPermission(String permission) {20         if (permission == null) {21             throw new IllegalArgumentException("permission is null");22         }23 24         if (!Process.supportsProcesses()) {25             return PackageManager.PERMISSION_GRANTED;26         }27         int pid = Binder.getCallingPid();28         if (pid != Process.myPid()) {29             return checkPermission(permission, pid,30                     Binder.getCallingUid());31         }32         return PackageManager.PERMISSION_DENIED;33     }

ActivityManagerNative.getDefault() 返回 IActivityManager，拿到ActivityManagerProxy对象的引用

static public IActivityManager getDefault()     {         if (gDefault != null) {             return gDefault;         }         IBinder b = ServiceManager.getService("activity");         gDefault = asInterface(b);         return gDefault;     } 

找到ActivityManagerNative.java?

public int checkPermission(String permission, int pid, int uid)throws RemoteException {         Parcel data = Parcel.obtain();         Parcel reply = Parcel.obtain();         data.writeInterfaceToken(IActivityManager.descriptor);         data.writeString(permission);         data.writeInt(pid);         data.writeInt(uid);         mRemote.transact(CHECK_PERMISSION_TRANSACTION, data, reply, 0);         reply.readException();         int res = reply.readInt();         data.recycle();         reply.recycle();         return res;}

通过Binder机制调用到onTransact

public boolean onTransact(int code, Parcel data, Parcel reply, int flags) throws RemoteException {        case CHECK_PERMISSION_TRANSACTION: {             data.enforceInterface(IActivityManager.descriptor);             String perm = data.readString();             int pid = data.readInt();             int uid = data.readInt();             int res = checkPermission(perm, pid, uid);             reply.writeNoException();             reply.writeInt(res);             return true;         }         .................}

找到ActivityManagerService.java?

    public static IPackageManager getPackageManager() {         if (sPackageManager != null) {             return sPackageManager;         }         IBinder b = ServiceManager.getService("package");         sPackageManager = IPackageManager.Stub.asInterface(b);         return sPackageManager;     }

?转到PackageManagerService.java

    public int checkUidPermission(String permName, int uid) {         synchronized (mPackages) {             Object obj = mSettings.getUserIdLP(uid);             if (obj != null) {                 GrantedPermissions gp = (GrantedPermissions)obj;                 if (gp.grantedPermissions.contains(permName)) {                     return PackageManager.PERMISSION_GRANTED;                 }             } else {                 HashSet<String> perms = mSystemPermissions.get(uid);                 if (perms != null && perms.contains(permName)) {                     return PackageManager.PERMISSION_GRANTED;                 }             }         }         return PackageManager.PERMISSION_DENIED;     }