【COM】异步通知 ExecNotificationQueryAsync 的使用问题

概述：异步通知 IWbemServices::ExecNotificationQueryAsync 的使用问题。调用 CancelAsyncCall 之后导致程序崩溃。

代码参考微软官方示例：示例：通过 WMI 接收事件通知 - Win32 apps | Microsoft Learn

0x01 复现场景

  • 环境：windows server 2008

参考微软官方代码实现一个进程，使用 windbg 加载进程，然后等待进程结束，就能看到 windbg 报错 0xC0000005。

0x02 dmp分析

  1. 报错详情

    （调用 CancelAsyncCall 的进程）主要问题还是访问了空指针导致的，并且是 ecx。是类成员函数调用时出现异常。this 指针为空。

  2. 堆栈

    确定是 RPC 调用。下一步查询下 RPC 调用方。

    ole32!GetChannelCallMgr 函数原型：

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    HRESULT GetChannelCallMgr(RPCOLEMESSAGE *pMsg, IUnknown * pStub,
                              IUnknown *pServer, CRpcChannelBuffer::CServerCallMgr **ppStubBuffer)

    直接看第一个参数 pMsg 。

  3. 查看下调用方

    成员变量 reserverd1 保存了RPC相关信息。 先 dds 再 dt 查看其内容。

    CAsyncCall 的成员可以查看 Windows-Server-2003/com/ole32/com/dcomrem/call.hxx at 5c6fe3db626b63a384230a1aa6b92ac416b0765f · selfrender/Windows-Server-2003 中相关源码。

    成员变量 _hRPC 来自于其继承的父类 CMessageCall

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    293   handle_t            _hRpc;      // Call handle (not binding handle).

    _hRpc 记录了调用方的句柄。查看 0x0479ba28 内存，在其附近找到了调用方的 PID 和 TID。如下图所示：

  4. 看下 PID 对应的进程，如下图所示：

    unsecapp 也就是我们注册的异步通知的通知方。

0x03 问题分析

基本分析完 dmp 文件之后，可以确定是我们注册的异步通知在程序结束时被调用了，导致 unsecapp 通知过来之后，调用了空指针。

为什么会出现这种问题，可以看下 unsecapp 的堆栈，上边已经看到了具体的pid和tid，1b34.1b48, 这就直接看线程 1b38 的堆栈就可以了。

堆栈如下所示：

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   0  Id: 1b34.1b38 Suspend: 1 Teb: 7ffdf000 Unfrozen
 # ChildEBP RetAddr      Args to Child              
00 0018e8b0 773354ac     76d6a8b7 00000002 0018e904 ntdll!KiFastSystemCallRet (FPO: [0,0,0])
01 0018e8b4 76d6a8b7     00000002 0018e904 00000001 ntdll!NtWaitForMultipleObjects+0xc (FPO: [5,0,0])
02 0018e950 77420f8d     0018e904 0018e978 00000000 kernel32!WaitForMultipleObjectsEx+0x11d (FPO: [Non-Fpo])
03 0018e9a4 76832507     0000002c 0018e9ec ffffffff USER32!RealMsgWaitForMultipleObjectsEx+0x13c (FPO: [Non-Fpo])
04 0018e9cc 768325bc     0018e9ec ffffffff 0018e9fc ole32!CCliModalLoop::BlockFn+0x97 (FPO: [Non-Fpo]) (CONV: thiscall) [d:\longhorn\com\ole32\com\dcomrem\callctrl.cxx @ 1162] 
05 0018e9f4 76938f62     ffffffff 002c27a0 0018eb00 ole32!ModalLoop+0x5b (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\chancont.cxx @ 211] 
06 0018ea10 76939ce1     00000000 0018eb14 00000000 ole32!ThreadSendReceive+0x12c (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 4831] 
07 0018ea38 76939b4d     0018eb00 002cf4d8 0018eb5c ole32!CRpcChannelBuffer::SwitchAptAndDispatchCall+0x194 (FPO: [Non-Fpo]) (CONV: thiscall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 4386] 
08 0018eb18 76833f94     002cf4d8 0018ec40 0018ec24 ole32!CRpcChannelBuffer::SendReceive2+0xef (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 4009] 
09 0018eb34 76833f46     0018ec40 0018ec24 002cf4d8 ole32!CCliModalLoop::SendReceive+0x1e (FPO: [Non-Fpo]) (CONV: thiscall) [d:\longhorn\com\ole32\com\dcomrem\callctrl.cxx @ 849] 
0a 0018ebac 76853811     002cf4d8 0018ec40 0018ec24 ole32!CAptRpcChnl::SendReceive+0x73 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\callctrl.cxx @ 578] 
0b 0018ec00 7712074c     002cf4d8 0018ec40 0018ec24 ole32!CCtxComChnl::SendReceive+0x1c5 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\ctxchnl.cxx @ 734] 
0c 0018ec18 771207ad     002a37bc 0018ecdc 771211b0 RPCRT4!NdrProxySendReceive+0x43
0d 0018ec24 771211b0     45542f97 0018f0d8 070001f3 RPCRT4!NdrpProxySendReceive+0xc (FPO: [0,0,0])
0e 0018f09c 77120822     70b62ba8 70b621fc 0018f0d8 RPCRT4!NdrClientCall2+0x5e9
0f 0018f0c0 770aeb83     0018f0d8 00000004 0018f0f0 RPCRT4!ObjectStublessClient+0x6f
10 0018f0d0 6fc1a87e     002a37bc 00000000 80041032 RPCRT4!ObjectStubless+0xf
11 0018f0f0 004b2ec2     00eea0fc 00000000 80041032 fastprox!CSinkProxyBuffer::XSinkFacelet::SetStatus+0x2e (FPO: [Non-Fpo])
12 0018f128 770b3419     00262914 00000000 80041032 unsecapp!CStub::SetStatus+0x7b (FPO: [Non-Fpo])
13 0018f150 77121d35     004b2e47 0018f350 00000005 RPCRT4!Invoke+0x2a
14 0018f180 771220a1     00000000 002aeb9c 002df118 RPCRT4!NdrStubCall2+0x28a (FPO: [SEH])
15 0018f1c8 770b6e5f     76866918 70b62ba8 00000000 RPCRT4!NdrStubCall2+0x4ab (FPO: [SEH])
16 0018f1cc 76866918     70b62ba8 00000000 00000000 RPCRT4!NdrpClientUnMarshal+0x464 (FPO: [SEH])
17 0018f574 77122465     002d1e78 002cf658 002c31b8 ole32!NdrOleAllocate
18 0018f5c4 6fc1a8b7     002d1e78 002c31b8 002cf658 RPCRT4!CStdStubBuffer_Invoke+0xa0 (FPO: [SEH])
19 0018f5d8 7693a8c5     00eea174 002c31b8 002cf658 fastprox!CSinkStubBuffer::XSinkStublet::Invoke+0x36 (FPO: [Non-Fpo])
1a 0018f620 7693aa59     002c31b8 002bd800 002b5eb0 ole32!SyncStubInvoke+0x3c (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 1161] 
1b 0018f66c 768661d6     002c31b8 002cfd60 00eea174 ole32!StubInvoke+0xb9 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 1372] 
1c 0018f748 768660e7     002cf658 00000000 00eea174 ole32!CCtxComChnl::ContextInvoke+0xfa (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\ctxchnl.cxx @ 1255] 
1d 0018f764 76866df5     002c31b8 00000001 00eea174 ole32!MTAInvoke+0x1a (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\callctrl.cxx @ 2020] 
1e 0018f790 7693a981     002c31b8 00000001 00eea174 ole32!STAInvoke+0x46 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\callctrl.cxx @ 1839] 
1f 0018f7c4 7693a79b     d0908070 002cf658 00eea174 ole32!AppInvoke+0xaa (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 1060] 
20 0018f8a0 7693ae2d     002c3160 002abff0 00000400 ole32!ComInvokeWithLockAndIPID+0x32c (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 1675] 
21 0018f8c8 76866bcd     002c3160 00000400 0029cc10 ole32!ComInvoke+0xc5 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\channelb.cxx @ 1445] 
22 0018f8dc 76866b8c     002c3160 0018f99c 00000400 ole32!ThreadDispatch+0x23 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\chancont.cxx @ 298] 
23 0018f920 7741fd72     00c600f6 00000400 0000babe ole32!ThreadWndProc+0x167 (FPO: [Non-Fpo]) (CONV: stdcall) [d:\longhorn\com\ole32\com\dcomrem\chancont.cxx @ 654] 
24 0018f94c 7741fe4a     76866aef 00c600f6 00000400 USER32!InternalCallWinProc+0x23
25 0018f9c4 7742018d     00000000 76866aef 00c600f6 USER32!UserCallWinProcCheckWow+0x14b (FPO: [Non-Fpo])
26 0018fa28 7742022b     76866aef 00000000 0018fa68 USER32!DispatchMessageWorker+0x322 (FPO: [Non-Fpo])
27 0018fa38 004b4fd7     0018fa4c 71b6d20c 004b9118 USER32!DispatchMessageW+0xf (FPO: [Non-Fpo])
28 0018fa68 004b6749     457c3509 004b954c 00000001 unsecapp!MessageLoop+0x28 (FPO: [Non-Fpo])
29 0018fa98 004b41a2     00000002 00262228 002614a0 unsecapp!main+0x38c (FPO: [Non-Fpo])
2a 0018fadc 76d6d411     7ffd7000 0018fb28 7731152f unsecapp!_initterm_e+0x163 (FPO: [Non-Fpo])
2b 0018fae8 7731152f     7ffd7000 772f5944 00000000 kernel32!BaseThreadInitThunk+0xe (FPO: [Non-Fpo])
2c 0018fb28 77311502     004b42dc 7ffd7000 ffffffff ntdll!__RtlUserThreadStart+0x23 (FPO: [Non-Fpo])
2d 0018fb40 00000000     004b42dc 7ffd7000 00000000 ntdll!_RtlUserThreadStart+0x1b (FPO: [Non-Fpo])

可以看到消息都是通过 DispatchMessageW 发送出去的。在后续rpc通知的时候，客户端可能已经调用了 CancelAsyncCall。当rpc执行的时候，就会出现崩溃问题。

0x04 解决方法

在 CancelAsyncCall 方法之后让当前线程阻塞一点时间，等待上次 unsecapp rpc调用结束，再调用 release 释放 IWbemServices 等相关对象。

补充

reserverd1 变量说明:

还是这个项目 selfrender/Windows-Server-2003: This is the leaked source code of Windows Server 2003

先看一下 CMessageCall 作为 CAsyncCall 的父类是有哪些成员的：

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//-----------------------------------------------------------------
//
//  Class:      CMessageCall
//
//  Purpose:    This class adds a message to the call info.  The
//              proxie's message is copied so the call can be
//              canceled without stray pointer references.
//
//-----------------------------------------------------------------
class CMessageCall : public ICancelMethodCalls, public IMessageParam
{
public:
    // Constructor and destructor
    CMessageCall();

protected:
    virtual ~CMessageCall();
    virtual void UninitCallObject();

public:
    // called before a call starts and after a call completes.
    virtual HRESULT InitCallObject(CALLCATEGORY callcat,
                           RPCOLEMESSAGE     *message,
                           DWORD              flags,
                           REFIPID            ipidServer,
                           DWORD              destctx,
                           COMVERSION         version,
                           CChannelHandle    *handle);

    // IUnknown methods
    STDMETHOD(QueryInterface)(REFIID riid, LPVOID *ppv)   = 0;
    STDMETHOD_(ULONG,AddRef)(void)                        = 0;
    STDMETHOD_(ULONG,Release)(void)                       = 0;

    // ICancelMethodCalls methods
    STDMETHOD(Cancel)(ULONG ulSeconds)                    = 0;
    STDMETHOD(TestCancel)(void)                           = 0;

    // Virtual methods needed by every call type for cancel support
    virtual void    CallCompleted   ( HRESULT hrRet )     = 0;
    virtual void    CallFinished    ()                    = 0;
    virtual HRESULT CanDispatch     ()                    = 0;
    virtual HRESULT WOWMsgArrived   ()                    = 0;
    virtual HRESULT GetState        ( DWORD *pdwState )   = 0;
    virtual BOOL    IsCallDispatched()                    = 0;
    virtual BOOL    IsCallCompleted ()                    = 0;
    virtual BOOL    IsCallCanceled  ()                    = 0;
    virtual BOOL    IsCancelIssued  ()                    = 0;
    virtual BOOL    HasWOWMsgArrived()                    = 0;
    virtual BOOL    IsClientWaiting ()                    = 0;
    virtual void    AckCancel       ()                    = 0;
    virtual HRESULT Cancel          (BOOL fModalLoop,
                                     ULONG ulTimeout)     = 0;
    virtual HRESULT AdvCancel       ()                    = 0;
    virtual void    Abort()         { Win4Assert(!"Abort Called"); }

    // Query methods
    BOOL ClientAsync()     { return _iFlags & CALLFLAG_CLIENTASYNC; }
    BOOL ServerAsync()     { return _iFlags & CALLFLAG_SERVERASYNC; }
    BOOL CancelEnabled()   { return _iFlags & CALLFLAG_CANCELENABLED; }
    BOOL IsClientSide()    { return !(_iFlags & server_cs); }
    BOOL FakeAsync()       { return _iFlags & fake_async_cs; }
    BOOL FreeThreaded()    { return _iFlags & freethreaded_cs; }
    void Lock()            { _iFlags |= locked_cs; }
#if DBG == 1
    void SetNAToMTAFlag()  {_iFlags |= leave_natomta_cs;}
    void ResetNAToMTAFlag(){_iFlags &= ~leave_natomta_cs;}
    BOOL IsNAToMTAFlagSet(){ return _iFlags & leave_natomta_cs;}
    void SetNAToSTAFlag()  {_iFlags |= leave_natosta_cs;}
    void ResetNAToSTAFlag(){_iFlags &= ~leave_natosta_cs;}
    BOOL IsNAToSTAFlagSet(){ return _iFlags & leave_natosta_cs;}
#endif    
    BOOL Locked()          { return _iFlags & locked_cs; }
    BOOL Neutral()         { return _iFlags & neutral_cs; }
    BOOL ProcessLocal()    { return _iFlags & process_local_cs; }
    BOOL ThreadLocal()     { return _iFlags & thread_local_cs; }
    BOOL Proxy()           { return _iFlags & proxy_cs; }
    BOOL Server()          { return _iFlags & server_cs; }

    // Get methods
    DWORD GetTimeout();
    DWORD GetDestCtx()           { return _destObj.GetDestCtx(); }
    COMVERSION &GetComVersion()  { return _destObj.GetComVersion(); }
    CCtxCall *GetClientCtxCall() { return m_pClientCtxCall; }
    CCtxCall *GetServerCtxCall() { return m_pServerCtxCall; }
    BOOL GetErrorFromPolicy()    { return (_iFlags & CALLFLAG_ERRORFROMPOLICY); }

    HRESULT      SetCallerhWnd();
    HWND         GetCallerhWnd()  { return _hWndCaller; }
    HANDLE       GetEvent()       { return _hEvent; }
    CALLCATEGORY GetCallCategory(){ return _callcat; }
    HRESULT      GetResult()      { return _hResult; }
    void         SetResult(HRESULT hr)  { _hResult = hr; }
    DWORD        GetFault()       { return _server_fault; }
    void         SetFault(DWORD fault) { _server_fault = fault; }
    IPID &       GetIPID()        { return _ipid; }
    HANDLE       GetSxsActCtx()   { return _hSxsActCtx; }

    // Set methods
    void SetThreadLocal(BOOL fThreadLocal);
    void SetClientCtxCall(CCtxCall *pCtxCall) { m_pClientCtxCall = pCtxCall; }
    void SetServerCtxCall(CCtxCall *pCtxCall) { m_pServerCtxCall = pCtxCall; }
    void SetClientAsync()                     { _iFlags |= CALLFLAG_CLIENTASYNC; }
    void SetServerAsync()                     { _iFlags |= CALLFLAG_SERVERASYNC; }
    void SetCancelEnabled()                   { _iFlags |= CALLFLAG_CANCELENABLED; }
    void SetErrorFromPolicy()                 { _iFlags |= CALLFLAG_ERRORFROMPOLICY; }
    void ResetErrorFromPolicy()               { _iFlags &= ~CALLFLAG_ERRORFROMPOLICY; }
    void SetSxsActCtx(HANDLE hCtx);

    // Other methods
    HRESULT RslvCancel(DWORD &dwSignal, HRESULT hrIn,
                       BOOL fPostMsg, CCliModalLoop *pCML);    
                       
protected:
    // Call object fields
    CALLCATEGORY        _callcat;   // call category
    DWORD               _iFlags;    // EChannelState
    SCODE               _hResult;   // HRESULT or exception code
    HANDLE              _hEvent;    // caller wait event
    HWND                _hWndCaller;// caller apartment hWnd (only used InWow)
    IPID                _ipid;      // ipid of interface call is being made on
    HANDLE              _hSxsActCtx;// Activation context active in the caller's context

public:
    // Channel fields
    DWORD               _server_fault;
    CDestObject         _destObj;
    void               *_pHeader;
    CChannelHandle     *_pHandle;
    handle_t            _hRpc;      // Call handle (not binding handle).
    IUnknown           *_pContext;

    // Structure
    RPCOLEMESSAGE        message;
    SChannelHookCallInfo hook;
    DWORD                _dwErrorBufSize;

protected:
    // Cancel fields
    ULONG     m_ulCancelTimeout;   // Seconds to wait before canceling the call
    DWORD     m_dwStartCount;      // Tick count at the time the call was made
    CCtxCall *m_pClientCtxCall;    // Client side context call object
    CCtxCall *m_pServerCtxCall;    // Server side context call object
};
  • 134行 message 成员的结构体就是我们用来解析 reserved1 成员时使用的结构体。

可以使用 RPCOLEMESSAGE 的原因就是因为在 CAsyncCall 的另外一个函数中，当 RPC 服务端响应时，reserved1 被 _hRPC 赋值了。而 _hRpc 则是在rpc建立连接时绑定的（调用函数为 RpcBindingInqAuthInfoExW 函数 (rpcdce.h) - Win32 apps | Microsoft Learn）。

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inline void CAsyncCall::ServerReply()
{
    Win4Assert( _hRpc != NULL );

    if (_hResult != S_OK)
    {
        I_RpcAsyncAbortCall( &_AsyncState, _hResult );
    }
    else
    {
        // Ignore errors because replies can fail.
        message.reserved1  = _hRpc;
        I_RpcSend( (RPC_MESSAGE *) &message );
    }
}
A_OS > Windows > COM
#RPC #调试 #COM
【COM】异步通知 ExecNotificationQueryAsync 的使用问题
https://hodlyounger.github.io/A_OS/Windows/COM/【COM】异步通知的使用问题/
作者
mingming
发布于
2024年2月6日
许可协议