Taking Object Ownership in C++

The following example tries to change the DACL of a file object by taking ownership of that object. This will succeed only if the caller has WRITE_DAC access to the object or is the owner of the object. If the initial attempt to change the DACL fails, an administrator can take ownership of the object. To give the administrator ownership, the example enables the SE_TAKE_OWNERSHIP_NAME privilege in the caller's access token, and makes the local system's Administrators group the owner of the object. If the caller is a member of the Administrators group, the code will then be able to change the object's DACL.

To enable and disable privileges, this example uses the SetPrivilege sample function described in Enabling and Disabling Privileges in C++.


#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;

}


 

 

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