Calling MSVC DLL procedure from MSVB service to create mutex.

Category:

System/API

Type:

Snippets

Difficulty:

Beginning

Author: Anonymous

Version Compatibility: Visual Basic 6

More information:

This code shows (1) how one can create an MSVC 6 DLL with a procedure that can be called from an MSVB 6 program and (2) how to create a mutex in a service with security that allows a nonservice process to use it.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
' (None)

Code:

I had to write an MSVC DLL because I needed to change the security on a mutex created by a service so that another process that was not a service could open the mutex.  I could not find a way to do this task in MSVB.

I used "File > New > Projects > Win 32 Dynamic-Link Library" in the MSVC 6 IDE to create a project "MyProject".  In the resulting CPP file, I added the following:

//   Function
//       GetAccessableMutex
//   Abstract
//       Wraps CreateMutex with the additional functionality for
creating security that may be more relaxed than is the default.  This
security will allow a service to create a mutex that an ordinary
process can use.  See the CreateMutex documentation in MSDN Library.
//   Arguments
//       bInitialOwner input Specifies the initial owner of the mutex
object.  If this value is TRUE and the caller created the mutex, the
calling thread obtains ownership of the mutex object.  Otherwise, the
calling thread does not obtain ownership of the mutex.
//       szName   input Pointer to a null-terminated string specifying
the name of the mutex object.  The name is limited to MAX_PATH
characters.  Name comparison is case sensitive.
//       hMutex   output Handle to the mutex object.
//   Return
//       Value from GetLastError.
//   Notes
//  2003.12.11:Alan Barksdale:Created.  See:
//   "Mutex Madness" in "Ask Dr. GUI #49" (November/December 1999)
<http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaskdr/html/drgui49.asp>.
//   "How do you call a Visual C++ (DLL) function from Visual Basic"
in comp.lang.basic.visual.misc and microsoft.public.vb.3rdparty in
USENET <http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm=97bcs6%24god%242%40news3.inter.net.il&rnum=1&prev=/groups%3Fq%3Dreference%2B%2522msvc%2Bdll%2522%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3D97bcs6%2524god%25242%2540news3.inter.net.il%26rnum%3D1>.
//   "Microsoft Knowledge Base Article - 106387, HOWTO: Share Kernel
Objects Between Processes"
<http://support.microsoft.com/default.aspx?scid=kb;en-us;106387>.
DWORD MYPROJECT_API_STD GetAccessableMutex( BOOL bInitialOwner, LPTSTR
szName, PHANDLE phMutex )
{
    SID_IDENTIFIER_AUTHORITY siaNT = SECURITY_NT_AUTHORITY;
 DWORD dwGottenLastError ; //   Last error from GetLastError
    PSID psidAuthenticatedUsers = NULL; 
    HANDLE hMutex = NULL  ;
    int nSidSize ; 
    int nAclSize ;
    PACL paclNewDacl = NULL; 
    SECURITY_DESCRIPTOR sd ;
    SECURITY_ATTRIBUTES sa ; 
    
    __try{
  SetLastError(ERROR_SUCCESS) ;
  *phMutex = NULL ;

// Create the Authenticated Users user group sid.
  if (!AllocateAndInitializeSid(&siaNT, 1,
SECURITY_AUTHENTICATED_USER_RID, 0,
                                           0, 0, 0, 0, 0, 0,
&psidAuthenticatedUsers))
        {
            psidAuthenticatedUsers = NULL ; 
            __leave;
        }
 
        nSidSize = GetLengthSid(psidAuthenticatedUsers) ;
  nAclSize = nSidSize + sizeof(ACCESS_ALLOWED_ACE) + sizeof(ACL) ;
        paclNewDacl = (PACL) LocalAlloc( LPTR, nAclSize ) ;
        if( !paclNewDacl )
            __leave ; 
        if(!InitializeAcl( paclNewDacl, nAclSize, ACL_REVISION ))
            __leave ; 
        // I am using GENERIC_ALL here so that this very code can be
applied to
        // other objects.  Specific access should be applied when
possible.
        if(!AddAccessAllowedAce( paclNewDacl, ACL_REVISION,
GENERIC_ALL, psidAuthenticatedUsers ))
            __leave ; 
        if(!InitializeSecurityDescriptor( &sd,
SECURITY_DESCRIPTOR_REVISION ))
            __leave ; 
        if(!SetSecurityDescriptorDacl( &sd, TRUE, paclNewDacl, FALSE
))
            __leave ; 
        sa.nLength = sizeof( sa ) ;
        sa.bInheritHandle = FALSE ; 
        sa.lpSecurityDescriptor = &sd ;
 
        *phMutex = CreateMutex( &sa, bInitialOwner, szName ) ;
        if( !hMutex )
            hMutex = OpenMutex( SYNCHRONIZE, FALSE, szName ) ;
    }__finally{
        if( !paclNewDacl )
            LocalFree( paclNewDacl ) ;
        if( !psidAuthenticatedUsers )
            FreeSid( psidAuthenticatedUsers ) ;

}
 
    dwGottenLastError = GetLastError() ;
    return dwGottenLastError ; 
} // GetAccessableMutex

I used "File > New > Projects > MFC AppWizard (dll)" to create a dummy
project just so that I would have a DEF file template.  I modified the
DEF file as follows:

; MYPROJECT.def : Declares the module parameters for the DLL.

LIBRARY      "MyProject"
DESCRIPTION  'MyProject Windows Dynamic Link Library'

EXPORTS
    ; Explicit exports can go here
 GetAccessableMutex

In MyProject.dsp I added the following after the analogous lines for
MyProject.cpp:

# Begin Source File

SOURCE=.\MYPROJECT.def
# End Source File

I modified MyProject.h as follows:

#ifdef MYPROJECT_EXPORTS
#define MYPROJECT_API __declspec(dllexport)
#define MYPROJECT_API_STD __stdcall
#else
#define MYPROJECT_API __declspec(dllimport)
#endif

extern "C" DWORD MYPROJECT_API_STD GetAccessableMutex( BOOL
bInitialOwner, LPTSTR szName, PHANDLE phMutex );

In my MSVB 6 program, I declared the function as follows:

'   Wraps CreateMutex with the additional functionality for creating
security that may be more relaxed than is the default.  This security
will allow a service to create a mutex that an ordinary process can
use.
Private Declare Function GetAccessableMutex Lib "MyProject.dll" ( _
    ByVal bInitialOwner As Long, _
    ByVal szName As String, _
    ByRef lHandle As Long _
) As Long

I called the function as follows in my MSVB 6 program:

Dim lGottenLastError As Long ' Last error from GetLastError in
MSVC DLL.  Would use Err.LastDllError if called the Win32 API
procedure in this process.

lGottenLastError = GetAccessableMutex(APIFALSE, sName, lHandle)

If ERROR_ALREADY_EXISTS = lGottenLastError Then
        ' Log that the mutex already exists.
    ElseIf ERROR_SUCCESS <> lGottenLastError Then
        ' Raise an error.
    End If