| Platform SDK: Access Control |
The following example uses the LogonUser function to start a new logon session for a client. The example gets the logon SID from the client's access token, and uses it to add access-control entries (ACEs) to the DACLs of the interactive window station and desktop. The ACEs allow the client access to the interactive desktop for the duration of the logon session. Next, the example calls the ImpersonateLoggedOnUser function to ensure that it has access to the client's executable file. A call to the CreateProcessAsUser function creates the client's process, specifying that it run in the interactive desktop. Before the function returns, it calls the RevertToSelf function to end the caller's impersonation of the client.
This sample calls the GetLogonSID and FreeLogonSID sample functions described in Getting the Logon SID.
BOOL AddAceToWindowStation(HWINSTA hwinsta, PSID psid);
BOOL AddAceToDesktop(HDESK hdesk, PSID psid);
BOOL StartInteractiveClientProcess (
LPTSTR lpszUsername, // client to log on
LPTSTR lpszDomain, // domain of client's account
LPTSTR lpszPassword, // client's password
LPTSTR lpCommandLine // command line to execute
)
{
HANDLE hToken;
HDESK hdesk = NULL;
HWINSTA hwinsta = NULL, hwinstaSave = NULL;
PROCESS_INFORMATION pi;
PSID pSid = NULL;
STARTUPINFO si;
BOOL bResult = FALSE;
// Log the client on to the local computer.
if (!LogonUser(
lpszUsername,
lpszDomain,
lpszPassword,
LOGON32_LOGON_INTERACTIVE,
LOGON32_PROVIDER_DEFAULT,
&hToken) )
{
goto Cleanup;
}
// Save a handle to the caller's current window station.
if ( (hwinstaSave = GetProcessWindowStation() ) == NULL)
goto Cleanup;
// Get a handle to the interactive window station.
hwinsta = OpenWindowStation(
"winsta0", // the interactive window station
FALSE, // handle is not inheritable
READ_CONTROL | WRITE_DAC); // rights to read/write the DACL
if (hwinsta == NULL)
goto Cleanup;
// To get the correct default desktop, set the caller's
// window station to the interactive window station.
if (!SetProcessWindowStation(hwinsta))
goto Cleanup;
// Get a handle to the interactive desktop.
hdesk = OpenDesktop(
"default", // the interactive window station
0, // no interaction with other desktop processes
FALSE, // handle is not inheritable
READ_CONTROL | // request the rights to read and write the DACL
WRITE_DAC |
DESKTOP_WRITEOBJECTS |
DESKTOP_READOBJECTS);
// Restore the caller's window station.
if (!SetProcessWindowStation(hwinstaSave))
goto Cleanup;
if (hdesk == NULL)
goto Cleanup;
// Get the SID for the client's logon session.
if (!GetLogonSID(hToken, &pSid))
goto Cleanup;
// Allow logon SID full access to interactive window station.
if (! AddAceToWindowStation(hwinsta, pSid) )
goto Cleanup;
// Allow logon SID full access to interactive desktop.
if (! AddAceToDesktop(hdesk, pSid) )
goto Cleanup;
// Impersonate client to ensure access to executable file.
if (! ImpersonateLoggedOnUser(hToken) )
goto Cleanup;
// Initialize the STARTUPINFO structure.
// Specify that the process runs in the interactive desktop.
ZeroMemory(&si, sizeof(STARTUPINFO));
si.cb= sizeof(STARTUPINFO);
si.lpDesktop = TEXT("winsta0\\default");
// Launch the process in the client's logon session.
bResult = CreateProcessAsUser(
hToken, // client's access token
NULL, // file to execute
lpCommandLine, // command line
NULL, // pointer to process SECURITY_ATTRIBUTES
NULL, // pointer to thread SECURITY_ATTRIBUTES
FALSE, // handles are not inheritable
NORMAL_PRIORITY_CLASS | CREATE_NEW_CONSOLE, // creation flags
NULL, // pointer to new environment block
NULL, // name of current directory
&si, // pointer to STARTUPINFO structure
&pi // receives information about new process
);
// End impersonation of client.
RevertToSelf();
if (bResult && pi.hProcess != INVALID_HANDLE_VALUE)
{
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(pi.hProcess);
}
if (pi.hThread != INVALID_HANDLE_VALUE)
CloseHandle(pi.hThread);
Cleanup:
if (hwinstaSave != NULL)
SetProcessWindowStation (hwinstaSave);
// Free the buffer for the logon SID.
if (pSid)
FreeLogonSID(&pSid);
// Close the handles to the interactive window station and desktop.
if (hwinsta)
CloseWindowStation(hwinsta);
if (hdesk)
CloseDesktop(hdesk);
// Close the handle to the client's access token.
if (hToken != INVALID_HANDLE_VALUE)
CloseHandle(hToken);
return bResult;
}
BOOL AddAceToWindowStation(HWINSTA hwinsta, PSID psid)
{
ACCESS_ALLOWED_ACE *pace;
ACL_SIZE_INFORMATION aclSizeInfo;
BOOL bDaclExist;
BOOL bDaclPresent;
BOOL bSuccess = FALSE;
DWORD dwNewAclSize;
DWORD dwSidSize = 0;
DWORD dwSdSizeNeeded;
PACL pacl;
PACL pNewAcl;
PSECURITY_DESCRIPTOR psd = NULL;
PSECURITY_DESCRIPTOR psdNew = NULL;
PVOID pTempAce;
SECURITY_INFORMATION si = DACL_SECURITY_INFORMATION;
unsigned int i;
__try
{
// Obtain the DACL for the window station.
if (!GetUserObjectSecurity(
hwinsta,
&si,
psd,
dwSidSize,
&dwSdSizeNeeded)
)
if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)
{
psd = (PSECURITY_DESCRIPTOR)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwSdSizeNeeded);
if (psd == NULL)
__leave;
psdNew = (PSECURITY_DESCRIPTOR)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwSdSizeNeeded);
if (psdNew == NULL)
__leave;
dwSidSize = dwSdSizeNeeded;
if (!GetUserObjectSecurity(
hwinsta,
&si,
psd,
dwSidSize,
&dwSdSizeNeeded)
)
__leave;
}
else
__leave;
// Create a new DACL.
if (!InitializeSecurityDescriptor(
psdNew,
SECURITY_DESCRIPTOR_REVISION)
)
__leave;
// Get the DACL from the security descriptor.
if (!GetSecurityDescriptorDacl(
psd,
&bDaclPresent,
&pacl,
&bDaclExist)
)
__leave;
// Initialize the ACL.
ZeroMemory(&aclSizeInfo, sizeof(ACL_SIZE_INFORMATION));
aclSizeInfo.AclBytesInUse = sizeof(ACL);
// Call only if the DACL is not NULL.
if (pacl != NULL)
{
// get the file ACL size info
if (!GetAclInformation(
pacl,
(LPVOID)&aclSizeInfo,
sizeof(ACL_SIZE_INFORMATION),
AclSizeInformation)
)
__leave;
}
// Compute the size of the new ACL.
dwNewAclSize = aclSizeInfo.AclBytesInUse + (2*sizeof(ACCESS_ALLOWED_ACE)) +
(2*GetLengthSid(psid)) - (2*sizeof(DWORD));
// Allocate memory for the new ACL.
pNewAcl = (PACL)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwNewAclSize);
if (pNewAcl == NULL)
__leave;
// Initialize the new DACL.
if (!InitializeAcl(pNewAcl, dwNewAclSize, ACL_REVISION))
__leave;
// If DACL is present, copy it to a new DACL.
if (bDaclPresent)
{
// Copy the ACEs to the new ACL.
if (aclSizeInfo.AceCount)
{
for (i=0; i < aclSizeInfo.AceCount; i++)
{
// Get an ACE.
if (!GetAce(pacl, i, &pTempAce))
__leave;
// Add the ACE to the new ACL.
if (!AddAce(
pNewAcl,
ACL_REVISION,
MAXDWORD,
pTempAce,
((PACE_HEADER)pTempAce)->AceSize)
)
__leave;
}
}
}
// Add the first ACE to the window station.
pace = (ACCESS_ALLOWED_ACE *)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
sizeof(ACCESS_ALLOWED_ACE) + GetLengthSid(psid) -
sizeof(DWORD));
if (pace == NULL)
__leave;
pace->Header.AceType = ACCESS_ALLOWED_ACE_TYPE;
pace->Header.AceFlags = CONTAINER_INHERIT_ACE |
INHERIT_ONLY_ACE | OBJECT_INHERIT_ACE;
pace->Header.AceSize = sizeof(ACCESS_ALLOWED_ACE) +
GetLengthSid(psid) - sizeof(DWORD);
pace->Mask = GENERIC_ACCESS;
if (!CopySid(GetLengthSid(psid), &pace->SidStart, psid))
__leave;
if (!AddAce(
pNewAcl,
ACL_REVISION,
MAXDWORD,
(LPVOID)pace,
pace->Header.AceSize)
)
__leave;
// Add the second ACE to the window station.
pace->Header.AceFlags = NO_PROPAGATE_INHERIT_ACE;
pace->Mask = WINSTA_ALL;
if (!AddAce(
pNewAcl,
ACL_REVISION,
MAXDWORD,
(LPVOID)pace,
pace->Header.AceSize)
)
__leave;
// Set a new DACL for the security descriptor.
if (!SetSecurityDescriptorDacl(
psdNew,
TRUE,
pNewAcl,
FALSE)
)
__leave;
// Set the new security descriptor for the window station.
if (!SetUserObjectSecurity(hwinsta, &si, psdNew))
__leave;
// Indicate success.
bSuccess = TRUE;
}
__finally
{
// Free the allocated buffers.
if (pace != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)pace);
if (pNewAcl != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)pNewAcl);
if (psd != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)psd);
if (psdNew != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)psdNew);
}
return bSuccess;
}
BOOL AddAceToDesktop(HDESK hdesk, PSID psid)
{
ACL_SIZE_INFORMATION aclSizeInfo;
BOOL bDaclExist;
BOOL bDaclPresent;
BOOL bSuccess = FALSE;
DWORD dwNewAclSize;
DWORD dwSidSize = 0;
DWORD dwSdSizeNeeded;
PACL pacl;
PACL pNewAcl;
PSECURITY_DESCRIPTOR psd = NULL;
PSECURITY_DESCRIPTOR psdNew = NULL;
PVOID pTempAce;
SECURITY_INFORMATION si = DACL_SECURITY_INFORMATION;
unsigned int i;
__try
{
// Obtain the security descriptor for the desktop object.
if (!GetUserObjectSecurity(
hdesk,
&si,
psd,
dwSidSize,
&dwSdSizeNeeded))
{
if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)
{
psd = (PSECURITY_DESCRIPTOR)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwSdSizeNeeded );
if (psd == NULL)
__leave;
psdNew = (PSECURITY_DESCRIPTOR)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwSdSizeNeeded);
if (psdNew == NULL)
__leave;
dwSidSize = dwSdSizeNeeded;
if (!GetUserObjectSecurity(
hdesk,
&si,
psd,
dwSidSize,
&dwSdSizeNeeded)
)
__leave;
}
else
__leave;
}
// Create a new security descriptor.
if (!InitializeSecurityDescriptor(
psdNew,
SECURITY_DESCRIPTOR_REVISION)
)
__leave;
// Obtain the DACL from the security descriptor.
if (!GetSecurityDescriptorDacl(
psd,
&bDaclPresent,
&pacl,
&bDaclExist)
)
__leave;
// Initialize.
ZeroMemory(&aclSizeInfo, sizeof(ACL_SIZE_INFORMATION));
aclSizeInfo.AclBytesInUse = sizeof(ACL);
// Call only if NULL DACL.
if (pacl != NULL)
{
// Determine the size of the ACL information.
if (!GetAclInformation(
pacl,
(LPVOID)&aclSizeInfo,
sizeof(ACL_SIZE_INFORMATION),
AclSizeInformation)
)
__leave;
}
// Compute the size of the new ACL.
dwNewAclSize = aclSizeInfo.AclBytesInUse +
sizeof(ACCESS_ALLOWED_ACE) +
GetLengthSid(psid) - sizeof(DWORD);
// Allocate buffer for the new ACL.
pNewAcl = (PACL)HeapAlloc(
GetProcessHeap(),
HEAP_ZERO_MEMORY,
dwNewAclSize);
if (pNewAcl == NULL)
__leave;
// Initialize the new ACL.
if (!InitializeAcl(pNewAcl, dwNewAclSize, ACL_REVISION))
__leave;
// If DACL is present, copy it to a new DACL.
if (bDaclPresent)
{
// Copy the ACEs to our new ACL.
if (aclSizeInfo.AceCount)
{
for (i=0; i < aclSizeInfo.AceCount; i++)
{
// Get an ACE.
if (!GetAce(pacl, i, &pTempAce))
__leave;
// Add the ACE to the new ACL.
if (!AddAce(
pNewAcl,
ACL_REVISION,
MAXDWORD,
pTempAce,
((PACE_HEADER)pTempAce)->AceSize)
)
__leave;
}
}
}
// Add ACE to the DACL.
if (!AddAccessAllowedAce(
pNewAcl,
ACL_REVISION,
DESKTOP_ALL,
psid)
)
__leave;
// Set new DACL to the new security descriptor.
if (!SetSecurityDescriptorDacl(
psdNew,
TRUE,
pNewAcl,
FALSE)
)
__leave;
// Set the new security descriptor for the desktop object.
if (!SetUserObjectSecurity(hdesk, &si, psdNew))
__leave;
// Indicate success.
bSuccess = TRUE;
}
__finally
{
// Free buffers.
if (pNewAcl != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)pNewAcl);
if (psd != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)psd);
if (psdNew != NULL)
HeapFree(GetProcessHeap(), 0, (LPVOID)psdNew);
}
return bSuccess;
}