Special Edition Using Microsoft Windows XP Professional (3rd Edition)

2017-07-07 02:10:07

If your hard drive is formatted using the NTFS (NT File System) directory structure, and you're not using Simple File Sharing, you can assign control of who is permitted to access files and folders on a per-user or per-group basis.

To display or modify NTFS permissions, select a file or folder in Windows Explorer, right-click Properties, and select the Security tab, as shown in Figure 28.14.

Figure 28.14. You can use the NTFS Permissions dialog box to a folder to restrict access to both network and local users.

If the Security tab doesn't appear, see "Security Tab Is Not Present" in the "Troubleshooting" section at the end of this chapter.

In the top part of the dialog box is the list of users or user groups with access to the file or folder. You can select any of the names in the list to view their associated permissions in the bottom half of the dialog.

The permission properties can each be granted or revoked individually. The permissions are Full Control, Modify, Read & Execute, List Folder Contents, Read, and Write. Their properties are listed in Table 28.2.

Table 28.2. NTFS File Permission Settings and Their Functions
Permission	Properties
Full Control	Gives all the rights listed below, plus lets the user change the file's security and ownership settings.
Modify	Lets a user modify a file's contents or delete a file.
Read & Execute	Allows a user to read a file's contents and/or run an executable file as a program.
Read	Lets a user read a file's contents only.
Write	Lets a user create a new file, or write data in an existing file, but not read a file's contents. For a folder, lets users add new files to the folder but not view the folder's contents.

Note that each permission has both Allow and Deny check boxes. To get access to a given resource, a user must be explicitly listed with Allow checked or must belong to a listed group that has Allow checked, and must not be listed with Deny access or belong to any group with Deny marked. Deny preempts Allow.

All these permissions are additive. In other words, Read and Write can both be checked to combine the properties of both. Full Control could be marked Allow but Write marked Deny to give all access rights except writing. (This permission would be strange but possible.)

The most productive use of NTFS file permissions is to assign most rights by group membership. One exception is with user home directories or profile directories, to which you usually grant access only to the Administrators group and the individual owner.

TIP

If you edit Permissions, before you click OK or Apply, click the Advanced button and view the Effective Permissions tab, as discussed later in this chapter. Enter a few usernames to see that the permissions work out as you expected. If they do, only then should you click OK.

If you find that even Administrator can't gain the rights to delete a file or folder, see "Administrator Can't Delete File or Folder" in the "Troubleshooting" section at the end of this chapter.

Inheritance of Permissions

Normally, permissions are assigned to a folder (or drive), and all the folders and files within it inherit the permissions of the top-level folder. This makes it possible for you set permissions on just one object (folder), to manage possibly hundreds of other files and folders contained within. If necessary, explicit permissions can be set on a file or subfolder to add to or override the inherited permissions. Permissions displayed in the Security tab (as in Figure 28.13) will be grayed out if they have been inherited from a containing folder.

You can view or change the inheritance setting for a file or folder by clicking the Advanced button on the Security properties page. In Figure 28.15, the folder has a check in Inherit from Parent the Permission Entries that Apply to Child Objects. That's the usual case.

Figure 28.15. The Advanced Permissions dialog box lets you control the inheritance of permissions, and set detailed permissions for user and groups.

If you uncheck the box, Windows gives you the option of starting with a blank permissions list (Remove) or keeping a copy of the settings it had before (Copy). In either case, the item now has its own independent list of access rights, which you can edit at will.

When you change permissions on a folder, you may want to cancel any manually added permissions set on the files and folders it contains. Checking the Replace Permission Entries on All Child Objects box will reset the permissions on all files in this folder and in subfolders, and will force all subfolders to inherit permissions from this folder.

CAUTION

Changing the permissions of the root folder of the drive containing Windows may make your system unusable. It's best not to mess with the permissions of your boot (usually C:) drive.

Advanced Security Settings

If you edit access permissions in the Advanced Security Settings dialog, you can exercise more "fine grained" control over permissions. It's rarely necessary, but for your reference, Table 28.3 lists the available permission settings.

Table 28.3. NTFS Advanced File Permission Settings and Their Functions
Permission	Properties
Traverse Folder/Execute File	For folders, this special permission allows a user the right to move through a folder to which he or she doesn't have List access, to reach a file or folder to which he or she does have access. For files, this permission allows the running of applications. (This permission is necessary only if the user wasn't granted the Group policy "Bypass Traverse Checking".)
List Folder/Read Data	For folders, allows the user to view the names of files or sub-folders inside a folder. For files, allows the user to read the data in a file.
Read Attributes	Allows the user to view the attributes of the file or folder (that is, Hidden, Read-Only, or System).
Read Extended Attributes	Allows the user to view extended attributes of files or folders as defined by another program. (These attributes vary depending on the program.)
Create Files/Write Data	For folders, allows the user to create new files inside the folder. For files, allows the user to add new data or overwrite data inside existing files.
Create Folders/Append Data	For folders, allows the user to create new subfolders. For files, allows the user to append data to the end of an existing file. This permission does not pertain to deleting or overwriting existing data.
Write Attributes	Allows the user to change the attributes of the file or folder.
Write Extended Attributes	Allows the user to change the extended attributes of a file or folder.
Delete Subfolders and Files	For a folder, allows the user to delete subfolders and their contents. This permission applies even if the Delete permission has not been expressly granted on the individual subfolders or their files.
Delete	Allows or denies the user to delete the file. Even if Delete is denied, a user can still delete a file if he or she has Delete Subfolders and Files permission on the parent folder.
Read Permissions	Allows the user to view the file's or folder's permissions assigned to a file or folder.
Change Permissions	Allows the user to change the file's or folder's permissions.
Take Ownership	Allows the user to take ownership of a file or folder.

Viewing Effective Permissions

The Effective drive Permissions tab on the Advanced Security page lets you enter a username and see what privileges the user will have as a result of the current security settings on the file or folder, as shown in Figure 28.16.

Figure 28.16. Effective Permissions shows you how edited Permissions settings will work before they're actually applied to the file.

This dialog box displays the effective permissions as edited, before they are applied to the file folder. This lets you verify that the permissions you have set operate as desired before committing them to the file by clicking OK or Apply.

Access Auditing

The Advanced Security drive Settings dialog provides a way for you to monitor access to files and folders through the Event Log. The Auditing tab (see Figure 28.17) lets you specify users and access types to monitor, and whether to record log entries for successful access, failure to access, or both. Auditing can be set for the use of each access attribute that you can set with Permissions: List Folder, Write Data, and so on.

Figure 28.17. Auditing properties record events in the Security Event log whenever the selected access privileges succeed and/or fail.

Auditing is useful in several situations:

To determine what files and folders an errant application program is attempting to use

To monitor users for attempts to circumvent security

To keep a record of access to important documents

To enable auditing, locate the folder or file you want to monitor, view its Security properties, click Advanced, view the Auditing page, and click Add. Select a specific user or group (or Everyone), and check the desired events to audit. You can prevent a new audit setting from propagating into subfolders by checking Apply These Auditing Entries to Objects and/or Containers Within This Container Only. You can enable the resetting of audit properties of all subfolders and files by checking "Replace Auditing Entries on All Child Objects…"

An entry is made in the Security Event log for each audited access, so be careful if you are enabling auditing on the entire hard drive!

Taking Ownership of Files

Sometimes files or folders have security attributes set so stringently that even Administrator can't read or modify them. Usually this occurs when the file has permissions set only for its owner and not the usual list: Owner, Administrator, System, and Backup Operators, as when a user account is deleted. In this case, no user is able to access the files in that user's My Documents folder.

If you absolutely need to access such files, you can take ownership of the file or folder, and then assign permissions to read and write as appropriate. To take ownership of a file or folder

1.	Log on as Administrator.
2.	View the file or folder in Explorer, right-click it, and choose Properties.
3.	View the Security tab and click Advanced.
4.	View the Owner tab, and select Administrator (the user) or Administrators (the group) from the list. You may want to check the Replace Owner on Subcontainers box to change subfolders as well.
5.	Click OK.
6.	Add privileges as necessary to grant access to the desired user(s).

Assigning Permissions to Groups

It's common in an office environment to want shared folders that are accessible by some users and not by others. For instance, you may wish to put payroll information in a shared folder and grant access only to certain administrative employees. In a school environment, you might want some folders that are accessible only by teachers, and others accessible only by members of a particular class. If you're using Simple File Sharing, this isn't possible, but if you are using manual permissions, it's fairly straightforward.

The best practice in this case is to create local user groups, which are collections of users that can be given privileges that carry over to the group's members. You can add the group and assign permissions for specific folders and files without having to list each of the qualified users separately. Another benefit is that you can add and remove users from the group later on without having to modify the settings of the various folders.

To create local user groups, follow these steps:

1.	Right click My Computer, click Manage, and open Local Users and Groups; or, on a domain computer, click the Advanced button on the Advanced tab of the User Accounts control panel applet.
2.	Right-click the Group entry in the left pane.
3.	Select Actions, New Group.
4.	Enter a name for the new group, such as Accounting.
5.	Click Add and select users to add to the group.

To grant the group permissions to specific folders

1.	Highlight the folder or file in Windows Explorer.
2.	Right-click and select Sharing and Security.
3.	Select the Security tab and click Add.
4.	Select the group name (on a domain computer you may select domain groups or local groups by selecting Location and choosing a domain name or the local computer name).
5.	Click OK, and then check the appropriate permissions for the group to have.
6.	If Everyone or other groups are listed as having rights to this folder, you may want to select the group(s) and uncheck any undesired privileges. If the entry is grayed out, the privileges are inherited from a containing folder. In this case, select Advanced, uncheck Inherit from Parent, and choose Copy to retain copies of the current settings. You can then remove the entries you don't want.
7.	Important: Before you click OK to commit the changes, use the Effective Permissions tab on the Advanced Properties dialog to check the effective rights of a few different users to be sure that the rights are what you intend. Be sure that Administrator has at least taken ownership privileges.

If you find that a user has access to something he or she shouldn't, see "A User Has Access to a Restricted Object" in the "Troubleshooting" section at the end of the chapter.

Securing Your Printers

If you have a printer that uses expensive paper or ink, and are concerned that guests, kids or unauthorized persons might use your printer, you should know that printers can be secured in the same way that access is controlled for files and folders: through user and group privileges. In the case of printers, the privileges allow users to add jobs to the printer, delete other people's jobs, and so on.

On a domain network, the network manager usually takes care of this. And on a workgroup it's generally not important to restrict access to printers. If you are using Simple File Sharing, it's not even possible to set up specific printer access privileges.

If you decide to, however, you can set printer access permissions by right-clicking a printer in your Printers folder and selecting Properties. The Security properties tab resembles the properties tab of files and folders, and can be modified in the same way.