HOWTO: Manage User Privileges Programmatically in Windows NT

• Microsoft Win32 Application Programming Interface (API) included with:

      - Microsoft Windows NT, versions 3.51, 4.0
  

SUMMARY

In Windows NT, privileges are used to provide a means of access control that differs from discretionary access control. A system manager uses privileges to control which users/groups are able to manipulate various aspects of the system. An application may use privileges when it changes a system resource, such as the system time, or when it shuts down the system.

The User Manager tool can be used to grant and revoke privileges from accounts.

Windows NT 3.51 provides functionality which allows the developer to manage privileges programmatically. This functionality is made available through LSA (Local Security Authority).

An example of an application that would benefit from LSA is a service install program. If the service is configured to run under a user account, it is necessary for that account to have the SeServiceLogonRight "logon as a service" privilege. This article discusses how to take advantage of LSA to grant and revoke privileges from users and groups.

MORE INFORMATION

Managing user privileges can be achieved programmatically using the following steps:

1. Open the policy on the target machine with LsaOpenPolicy(). To grant privileges, open the policy with POLICY_CREATE_ACCOUNT and POLICY_LOOKUP_NAMES access. To revoke privileges, open the policy with POLICY_LOOKUP_NAMES access.

2. Obtain a SID (security identifier) representing the user/group of interest. The LookupAccountName() and LsaLookupNames() APIs can obtain a SID from an account name.

3. Call LsaAddAccountRights() to grant privileges to the user(s) represented by the supplied SID.

4. Call LsaRemoveAccountRights() to revoke privileges from the user(s) represented by the supplied SID.

5. Close the policy with LsaClose().

The LSA API LsaEnumerateAccountRights() can be used to determine which privileges have been granted to an account.

The LSA API LsaEnumerateAccountsWithUserRight() can be used to determine which accounts have been granted a specified privilege.

Documentation and header files for these LSA APIs is provided in the Windows 32 SDK in the MSTOOLS\SECURITY directory.

In the lastest versions of the Win32 SDK, the headers appear in the mstools\samples\win32\winnt\security\include directory and the documentation is in ....\security\lsasamp\lsaapi.hlp.

NOTE: These LSA APIs are currently implemented as Unicode only.

This sample will grant the privilege SeServiceLogonRight to the account specified on argv[1].

This sample is dependant on these import libs

   advapi32.lib (for LsaXxx)
   user32.lib (for wsprintf)

Sample Code

/*++

The optional target machine is specified as argv[2], otherwise, the account database is updated on the local machine.

The LSA APIs used by this sample are Unicode only.

Use LsaRemoveAccountRights() to remove account rights.

Scott Field (sfield)    12-Jul-95
--*/

#define UNICODE

#include <windows.h>
#include <stdio.h>

#include "ntsecapi.h"

    LPWSTR ServerName,          // machine to open policy on (Unicode)
    DWORD DesiredAccess,        // desired access to policy
    PLSA_HANDLE PolicyHandle    // resultant policy handle
    );

    LPTSTR SystemName,          // where to lookup account
    LPTSTR AccountName,         // account of interest
    PSID *Sid                   // resultant buffer containing SID
    );

    LSA_HANDLE PolicyHandle,    // open policy handle
    PSID AccountSid,            // SID to grant privilege to
    LPWSTR PrivilegeName,       // privilege to grant (Unicode)
    BOOL bEnable                // enable or disable
    );

    PLSA_UNICODE_STRING LsaString, // destination
    LPWSTR String                  // source (Unicode)
    );

    LPSTR szAPI,                // pointer to function name (ANSI)
    NTSTATUS Status             // NTSTATUS error value
    );

    LPSTR szAPI,                // pointer to function name (ANSI)
    DWORD WinError              // DWORD WinError
    );

#define RTN_OK 0
#define RTN_USAGE 1
#define RTN_ERROR 13

//
// If you have the ddk, include ntstatus.h.
//

#define STATUS_SUCCESS  ((NTSTATUS)0x00000000L)

int _cdecl

    LSA_HANDLE PolicyHandle;
    WCHAR wComputerName[256]=L"";   // static machine name buffer
    TCHAR AccountName[256];         // static account name buffer
    PSID pSid;
    NTSTATUS Status;
    int iRetVal=RTN_ERROR;          // assume error from main

    if(argc == 1)
    {
        fprintf(stderr,"Usage: %s <Account> [TargetMachine]\n",
            argv[0]);
        return RTN_USAGE;
    }

    //
    // Pick up account name on argv[1].
    // Assumes source is ANSI. Resultant string is ANSI or Unicode
    //
    wsprintf(AccountName, TEXT("%hS"), argv[1]);

    //
    // Pick up machine name on argv[2], if appropriate
    // assumes source is ANSI. Resultant string is Unicode.
    //
    if(argc == 3) wsprintfW(wComputerName, L"%hS", argv[2]);

    //
    // Open the policy on the target machine.
    //
    if((Status=OpenPolicy(
                wComputerName,      // target machine
                POLICY_CREATE_ACCOUNT | POLICY_LOOKUP_NAMES,
                &PolicyHandle       // resultant policy handle
                )) != STATUS_SUCCESS) {
        DisplayNtStatus("OpenPolicy", Status);
        return RTN_ERROR;
    }

    //
    // Obtain the SID of the user/group.
    // Note that we could target a specific machine, but we don't.
    // Specifying NULL for target machine searches for the SID in the
    // following order: well-known, Built-in and local, primary domain,
    // trusted domains.
    //
    if(GetAccountSid(
            NULL,       // default lookup logic
            AccountName,// account to obtain SID
            &pSid       // buffer to allocate to contain resultant SID
            )) {
        //
        // We only grant the privilege if we succeeded in obtaining the
        // SID. We can actually add SIDs which cannot be looked up, but
        // looking up the SID is a good sanity check which is suitable for
        // most cases.

        //
        // Grant the SeServiceLogonRight to users represented by pSid.
        //
        if((Status=SetPrivilegeOnAccount(
                    PolicyHandle,           // policy handle
                    pSid,                   // SID to grant privilege
                    L"SeServiceLogonRight", // Unicode privilege
                    TRUE                    // enable the privilege
                    )) == STATUS_SUCCESS)
            iRetVal=RTN_OK;
        else
            DisplayNtStatus("AddUserRightToAccount", Status);
    }
    else {
        //
        // Error obtaining SID.
        //
        DisplayWinError("GetAccountSid", GetLastError());
    }

    //
    // Close the policy handle.
    //
    LsaClose(PolicyHandle);

    //
    // Free memory allocated for SID.
    //
    if(pSid != NULL) HeapFree(GetProcessHeap(), 0, pSid);

    return iRetVal;

void InitLsaString(

    PLSA_UNICODE_STRING LsaString,
    LPWSTR String
    )

    DWORD StringLength;

    if (String == NULL) {
        LsaString->Buffer = NULL;
        LsaString->Length = 0;
        LsaString->MaximumLength = 0;
        return;
    }

    StringLength = wcslen(String);
    LsaString->Buffer = String;
    LsaString->Length = (USHORT) StringLength * sizeof(WCHAR);
    LsaString->MaximumLength=(USHORT)(StringLength+1) * sizeof(WCHAR);

NTSTATUS OpenPolicy(

    LPWSTR ServerName,
    DWORD DesiredAccess,
    PLSA_HANDLE PolicyHandle
    )

    LSA_OBJECT_ATTRIBUTES ObjectAttributes;
    LSA_UNICODE_STRING ServerString;
    PLSA_UNICODE_STRING Server = NULL;

    //
    // Always initialize the object attributes to all zeroes.
    //
    ZeroMemory(&ObjectAttributes, sizeof(ObjectAttributes));

    if (ServerName != NULL) {
        //
        // Make a LSA_UNICODE_STRING out of the LPWSTR passed in
        //
        InitLsaString(&ServerString, ServerName);
        Server = &ServerString;
    }

    //
    // Attempt to open the policy.
    //
    return LsaOpenPolicy(
                Server,
                &ObjectAttributes,
                DesiredAccess,
                PolicyHandle
                );
}

/*++

If the function succeeds, the return value is TRUE. A buffer is allocated which contains the SID representing the supplied account. This buffer should be freed when it is no longer needed by calling HeapFree(GetProcessHeap(), 0, buffer)

If the function fails, the return value is FALSE. Call GetLastError() to obtain extended error information.

Scott Field (sfield)    12-Jul-95
--*/

BOOL

    LPTSTR SystemName,
    LPTSTR AccountName,
    PSID *Sid
    )

    LPTSTR ReferencedDomain=NULL;
    DWORD cbSid=128;    // initial allocation attempt
    DWORD cchReferencedDomain=16; // initial allocation size
    SID_NAME_USE peUse;
    BOOL bSuccess=FALSE; // assume this function will fail

    __try {

    //
    // initial memory allocations
    //
    if((*Sid=HeapAlloc(
                    GetProcessHeap(),
                    0,
                    cbSid
                    )) == NULL) __leave;

    if((ReferencedDomain=HeapAlloc(
                    GetProcessHeap(),
                    0,
                    cchReferencedDomain * sizeof(TCHAR)
                    )) == NULL) __leave;

    //
    // Obtain the SID of the specified account on the specified system.
    //
    while(!LookupAccountName(
                    SystemName,         // machine to lookup account on
                    AccountName,        // account to lookup
                    *Sid,               // SID of interest
                    &cbSid,             // size of SID
                    ReferencedDomain,   // domain account was found on
                    &cchReferencedDomain,
                    &peUse
                    )) {
        if (GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
            //
            // reallocate memory
            //
            if((*Sid=HeapReAlloc(
                        GetProcessHeap(),
                        0,
                        *Sid,
                        cbSid
                        )) == NULL) __leave;

            if((ReferencedDomain=HeapReAlloc(
                        GetProcessHeap(),
                        0,
                        ReferencedDomain,
                        cchReferencedDomain * sizeof(TCHAR)
                        )) == NULL) __leave;
        }
        else __leave;
    }

    //
    // Indicate success.
    //
    bSuccess=TRUE;

    } // finally
    __finally {

    //
    // Cleanup and indicate failure, if appropriate.
    //

    HeapFree(GetProcessHeap(), 0, ReferencedDomain);

    if(!bSuccess) {
        if(*Sid != NULL) {
            HeapFree(GetProcessHeap(), 0, *Sid);
            *Sid = NULL;
        }
    }

    } // finally

    return bSuccess;

NTSTATUS SetPrivilegeOnAccount(

    LSA_HANDLE PolicyHandle,    // open policy handle
    PSID AccountSid,            // SID to grant privilege to
    LPWSTR PrivilegeName,       // privilege to grant (Unicode)
    BOOL bEnable                // enable or disable
    )

    LSA_UNICODE_STRING PrivilegeString;

    //
    // Create a LSA_UNICODE_STRING for the privilege name.
    //
    InitLsaString(&PrivilegeString, PrivilegeName);

    //
    // grant or revoke the privilege, accordingly
    //
    if(bEnable) {
        return LsaAddAccountRights(
                PolicyHandle,       // open policy handle
                AccountSid,         // target SID
                &PrivilegeString,   // privileges
                1                   // privilege count
                );
    }
    else {
        return LsaRemoveAccountRights(
                PolicyHandle,       // open policy handle
                AccountSid,         // target SID
                FALSE,              // do not disable all rights
                &PrivilegeString,   // privileges
                1                   // privilege count
                );
    }

void DisplayNtStatus(

    LPSTR szAPI,
    NTSTATUS Status
    )

    //
    // Convert the NTSTATUS to Winerror. Then call DisplayWinError().
    //
    DisplayWinError(szAPI, LsaNtStatusToWinError(Status));

void DisplayWinError(

    LPSTR szAPI,
    DWORD WinError
    )

    LPSTR MessageBuffer;
    DWORD dwBufferLength;

    //
    // TODO: Get this fprintf out of here!
    //
    fprintf(stderr,"%s error!\n", szAPI);

    if(dwBufferLength=FormatMessageA(
                        FORMAT_MESSAGE_ALLOCATE_BUFFER |
                        FORMAT_MESSAGE_FROM_SYSTEM,
                        NULL,
                        WinError,
                        GetUserDefaultLangID(),
                        (LPSTR) &MessageBuffer,
                        0,
                        NULL
                        ))
    {
        DWORD dwBytesWritten; // unused

        //
        // Output message string on stderr.
        //
        WriteFile(
            GetStdHandle(STD_ERROR_HANDLE),
            MessageBuffer,
            dwBufferLength,
            &dwBytesWritten,
            NULL
            );

        //
        // Free the buffer allocated by the system.
        //
        LocalFree(MessageBuffer);
    }