Übernehmen des Objektbesitzes in C++

Im folgenden Beispiel wird versucht, die DACL eines Dateiobjekts zu ändern, indem der Besitz dieses Objekts übernommen wird. Dies ist nur erfolgreich, wenn der Aufrufer WRITE_DAC Zugriff auf das Objekt hat oder besitzer des Objekts ist. Wenn der erste Versuch, die DACL zu ändern, fehlschlägt, kann ein Administrator den Besitz des Objekts übernehmen. Um dem Administrator den Besitz zu erteilen, aktiviert das Beispiel die SE_TAKE_OWNERSHIP_NAME-Berechtigung im Zugriffstoken des Aufrufers und macht die Administratorengruppe des lokalen Systems zum Besitzer des Objekts. Wenn der Aufrufer Mitglied der Gruppe Administratoren ist, kann der Code die DACL des Objekts ändern.

Zum Aktivieren und Deaktivieren von Berechtigungen verwendet dieses Beispiel die SetPrivilege-Beispielfunktion, die unter Aktivieren und Deaktivieren von Berechtigungen in C++ beschrieben wird.

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

//Forward declaration of SetPrivilege
BOOL SetPrivilege(
    HANDLE hToken,          // access token handle
    LPCTSTR lpszPrivilege,  // name of privilege to enable/disable
    BOOL bEnablePrivilege   // to enable or disable privilege
    ) ;


BOOL TakeOwnership(LPTSTR lpszOwnFile) 
{

    BOOL bRetval = FALSE;

    HANDLE hToken = NULL; 
    PSID pSIDAdmin = NULL;
    PSID pSIDEveryone = NULL;
    PACL pACL = NULL;
    SID_IDENTIFIER_AUTHORITY SIDAuthWorld =
            SECURITY_WORLD_SID_AUTHORITY;
    SID_IDENTIFIER_AUTHORITY SIDAuthNT = SECURITY_NT_AUTHORITY;
    const int NUM_ACES  = 2;
    EXPLICIT_ACCESS ea[NUM_ACES];
    DWORD dwRes;

    // Specify the DACL to use.
    // Create a SID for the Everyone group.
    if (!AllocateAndInitializeSid(&SIDAuthWorld, 1,
                     SECURITY_WORLD_RID,
                     0,
                     0, 0, 0, 0, 0, 0,
                     &pSIDEveryone)) 
    {
        printf("AllocateAndInitializeSid (Everyone) error %u\n",
                GetLastError());
        goto Cleanup;
    }

    // Create a SID for the BUILTIN\Administrators group.
    if (!AllocateAndInitializeSid(&SIDAuthNT, 2,
                     SECURITY_BUILTIN_DOMAIN_RID,
                     DOMAIN_ALIAS_RID_ADMINS,
                     0, 0, 0, 0, 0, 0,
                     &pSIDAdmin)) 
    {
        printf("AllocateAndInitializeSid (Admin) error %u\n",
                GetLastError());
        goto Cleanup;
    }

    ZeroMemory(&ea, NUM_ACES * sizeof(EXPLICIT_ACCESS));

    // Set read access for Everyone.
    ea[0].grfAccessPermissions = GENERIC_READ;
    ea[0].grfAccessMode = SET_ACCESS;
    ea[0].grfInheritance = NO_INHERITANCE;
    ea[0].Trustee.TrusteeForm = TRUSTEE_IS_SID;
    ea[0].Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP;
    ea[0].Trustee.ptstrName = (LPTSTR) pSIDEveryone;

    // Set full control for Administrators.
    ea[1].grfAccessPermissions = GENERIC_ALL;
    ea[1].grfAccessMode = SET_ACCESS;
    ea[1].grfInheritance = NO_INHERITANCE;
    ea[1].Trustee.TrusteeForm = TRUSTEE_IS_SID;
    ea[1].Trustee.TrusteeType = TRUSTEE_IS_GROUP;
    ea[1].Trustee.ptstrName = (LPTSTR) pSIDAdmin;

    if (ERROR_SUCCESS != SetEntriesInAcl(NUM_ACES,
                                         ea,
                                         NULL,
                                         &pACL))
    {
        printf("Failed SetEntriesInAcl\n");
        goto Cleanup;
    }

    // Try to modify the object's DACL.
    dwRes = SetNamedSecurityInfo(
        lpszOwnFile,                 // name of the object
        SE_FILE_OBJECT,              // type of object
        DACL_SECURITY_INFORMATION,   // change only the object's DACL
        NULL, NULL,                  // do not change owner or group
        pACL,                        // DACL specified
        NULL);                       // do not change SACL

    if (ERROR_SUCCESS == dwRes) 
    {
        printf("Successfully changed DACL\n");
        bRetval = TRUE;
        // No more processing needed.
        goto Cleanup;
    }
    if (dwRes != ERROR_ACCESS_DENIED)
    {
        printf("First SetNamedSecurityInfo call failed: %u\n",
                dwRes); 
        goto Cleanup;
    }

    // If the preceding call failed because access was denied, 
    // enable the SE_TAKE_OWNERSHIP_NAME privilege, create a SID for 
    // the Administrators group, take ownership of the object, and 
    // disable the privilege. Then try again to set the object's DACL.

    // Open a handle to the access token for the calling process.
    if (!OpenProcessToken(GetCurrentProcess(), 
                          TOKEN_ADJUST_PRIVILEGES, 
                          &hToken)) 
       {
          printf("OpenProcessToken failed: %u\n", GetLastError()); 
          goto Cleanup; 
       } 

    // Enable the SE_TAKE_OWNERSHIP_NAME privilege.
    if (!SetPrivilege(hToken, SE_TAKE_OWNERSHIP_NAME, TRUE)) 
    {
        printf("You must be logged on as Administrator.\n");
        goto Cleanup; 
    }

    // Set the owner in the object's security descriptor.
    dwRes = SetNamedSecurityInfo(
        lpszOwnFile,                 // name of the object
        SE_FILE_OBJECT,              // type of object
        OWNER_SECURITY_INFORMATION,  // change only the object's owner
        pSIDAdmin,                   // SID of Administrator group
        NULL,
        NULL,
        NULL); 

    if (dwRes != ERROR_SUCCESS) 
    {
        printf("Could not set owner. Error: %u\n", dwRes); 
        goto Cleanup;
    }
        
    // Disable the SE_TAKE_OWNERSHIP_NAME privilege.
    if (!SetPrivilege(hToken, SE_TAKE_OWNERSHIP_NAME, FALSE)) 
    {
        printf("Failed SetPrivilege call unexpectedly.\n");
        goto Cleanup;
    }

    // Try again to modify the object's DACL,
    // now that we are the owner.
    dwRes = SetNamedSecurityInfo(
        lpszOwnFile,                 // name of the object
        SE_FILE_OBJECT,              // type of object
        DACL_SECURITY_INFORMATION,   // change only the object's DACL
        NULL, NULL,                  // do not change owner or group
        pACL,                        // DACL specified
        NULL);                       // do not change SACL

    if (dwRes == ERROR_SUCCESS)
    {
        printf("Successfully changed DACL\n");
        bRetval = TRUE; 
    }
    else
    {
        printf("Second SetNamedSecurityInfo call failed: %u\n",
                dwRes); 
    }

Cleanup:

    if (pSIDAdmin)
        FreeSid(pSIDAdmin); 

    if (pSIDEveryone)
        FreeSid(pSIDEveryone); 

    if (pACL)
       LocalFree(pACL);

    if (hToken)
       CloseHandle(hToken);

    return bRetval;

}