CreateFileMapping and OpenFileMapping accross different users.

[Darrel Q Pham]

Hi guys, I'm a new programmer and I'm using CreateFileMapping in my service and trying to open it up with my Process with user A. OpenFileMapping with user A returns a file not found error. I know the file mapping works if I open two processes with the same user. I was able to get two services to share a file mapping correctly. So this must mean that the file mapping is out of scope to user A. Please help.

//Service
TCHAR SharedMemoryName[] = _T("Global\\Shared Memory1");

	HANDLE handle\_SharedMemory = CreateFileMappingA( 
		INVALID\_HANDLE\_VALUE,	// use paging file
		NULL,					// default security
		PAGE\_READWRITE,			// read/write access
		0,						// max. object size
		MAX\_SH\_MEM\_SIZE,		// buffer size
		(LPCSTR) SharedMemoryName ); //name of mapping object

//Process launched by user A
TCHAR SharedMemoryName[] = _T("Global\\Shared Memory1");

            HANDLE handle\_SharedMemory = OpenFileMappingA( 
		FILE\_MAP\_ALL\_ACCESS, //read/write access
		FALSE,				 //do not inherit the name
		(LPCSTR) SharedMemoryName ); //name of mapping object

[Lost User]

Have you enabled "Interact with desktop" for the service?

[Darrel Q Pham]

Yes it is enabled. Any other suggestions?

[Lost User]

What operating system is the service running on? Try using AdjustTokenPrivileges to set SeCreateGlobalPrivilege in the service before creating the mapping.

[Darrel Q Pham]

It still doesn't work. This is what I did. Perhaps I did something wrong here?

//Adjust Token and privileges to set global shared memory space
HANDLE l_handle_Token; //To Do Close handle
TOKEN_PRIVILEGES l_tokenprivileges_myPrivileges;

if( !OpenProcessToken( GetCurrentProcess(), TOKEN\_ADJUST\_PRIVILEGES | TOKEN\_QUERY, &l\_handle\_Token ) )
{
	WriteLog( g\_cLogFile, \_T("OpenProcessToken failed \\n")		);
	return (FALSE);
}

LUID l\_luid\_ID;	
if( !::LookupPrivilegeValue( NULL, SE\_CREATE\_GLOBAL\_NAME, &l\_luid\_ID ) )
{
	WriteLog( g\_cLogFile, \_T("LookupPrivilageValue failed \\n")		);
	CloseHandle( l\_handle\_Token );
	return (FALSE);
}
else 
{
	WriteLog( g\_cLogFile, \_T("LookupPrivilageValue successful \\n")		);
	l\_tokenprivileges\_myPrivileges.PrivilegeCount = 1;
	l\_tokenprivileges\_myPrivileges.Privileges\[0\].Luid = l\_luid\_ID;
	l\_tokenprivileges\_myPrivileges.Privileges\[0\].Attributes = SE\_PRIVILEGE\_ENABLED;
	AdjustTokenPrivileges( 
		l\_handle\_Token, 
		FALSE, 
		&l\_tokenprivileges\_myPrivileges, 
		sizeof(TOKEN\_PRIVILEGES), 
		(PTOKEN\_PRIVILEGES)NULL, 
		0 );
	CloseHandle( l\_handle\_Token );
}

[Darrel Q Pham]

I checked the service information with process explorer and it does show that SE_CREATE_GLOBAL_NAME(SeCreateGlobalPrivilege ) is set. CreateEvent(...) was set up and called similarly, and that works fine. I initially had problems with access violations with OpenEvent(...) but atleast I know there is something there, and I fixed that with creating an empty security attribute and passing that in with OpenEvent(...). This is beyond me. More ideas would greatly be appreciated.

[Darrel Q Pham]

Solution: The casting is wrong. Now I just have to find a way to pass my TCHAR array/string correctly.

g_handle_SharedMemory[i_counter] = CreateFileMapping(
INVALID_HANDLE_VALUE, // use paging file
&l_securityattributes_AllAccessAttr, // default security
PAGE_READWRITE, // read/write access
0, // max. object size
MAX_SH_MEM_SIZE, // buffer size
"Global\\Shared Memory" ); //name of mapping object

instead of

g_handle_SharedMemory[i_counter] = CreateFileMapping(
INVALID_HANDLE_VALUE, // use paging file
&l_securityattributes_AllAccessAttr, // default security
PAGE_READWRITE, // read/write access
0, // max. object size
MAX_SH_MEM_SIZE, // buffer size
(LPTSTR)Somestring ); //name of mapping object