Joining an NT Domain with Samba 2.2</emphasis>

- Joining an NT Domain with Samba 2.2</emphasis> + Joining an NT Domain with Samba 2.2 In order for a Samba-2 server to join an NT domain, you must first add the NetBIOS name of the Samba server to the @@ -165,4 +160,4 @@ the NIS/NT Samba. - +

+ + + + Viewing and changing UNIX permissions using the NT + security dialogs + + + New in the Samba 2.0.4 release is the ability for Windows + NT clients to use their native security settings dialog box to + view and modify the underlying UNIX permissions. + + Note that this ability is careful not to compromise + the security of the UNIX host Samba is running on, and + still obeys all the file permission rules that a Samba + administrator can set. + + In Samba 2.0.4 and above the default value of the + parameter + nt acl support has been changed from + false to true, so + manipulation of permissions is turned on by default. + + + + How to view file security on a Samba share + + From an NT 4.0 client, single-click with the right + mouse button on any file or directory in a Samba mounted + drive letter or UNC path. When the menu pops-up, click + on the Properties entry at the bottom of + the menu. This brings up the normal file properties dialog + box, but with Samba 2.0.4 this will have a new tab along the top + marked Security. Click on this tab and you + will see three buttons, Permissions, + Auditing, and Ownership. + The Auditing button will cause either + an error message A requested privilege is not held + by the client to appear if the user is not the + NT Administrator, or a dialog which is intended to allow an + Administrator to add auditing requirements to a file if the + user is logged on as the NT Administrator. This dialog is + non-functional with a Samba share at this time, as the only + useful button, the Add button will not currently + allow a list of users to be seen. + + + + Viewing file ownership + + Clicking on the "Ownership" button + brings up a dialog box telling you who owns the given file. The + owner name will be of the form : + + "SERVER\user (Long name)" + + Where SERVER is the NetBIOS name of + the Samba server, user is the user name of + the UNIX user who owns the file, and (Long name) + is the discriptive string identifying the user (normally found in the + GECOS field of the UNIX password database). Click on the Close + button to remove this dialog. + + If the parameter nt acl support + is set to false then the file owner will + be shown as the NT user "Everyone". + + The Take Ownership button will not allow + you to change the ownership of this file to yourself (clicking on + it will display a dialog box complaining that the user you are + currently logged onto the NT client cannot be found). The reason + for this is that changing the ownership of a file is a privilaged + operation in UNIX, available only to the root + user. As clicking on this button causes NT to attempt to change + the ownership of a file to the current user logged into the NT + client this will not work with Samba at this time. + + There is an NT chown command that will work with Samba + and allow a user with Administrator privillage connected + to a Samba 2.0.4 server as root to change the ownership of + files on both a local NTFS filesystem or remote mounted NTFS + or Samba drive. This is available as part of the Seclib + NT security library written by Jeremy Allison of + the Samba Team, available from the main Samba ftp site. + + + + + Viewing file or directory permissions + + The third button is the "Permissions" + button. Clicking on this brings up a dialog box that shows both + the permissions and the UNIX owner of the file or directory. + The owner is displayed in the form : + + "SERVER\user (Long name)" + + Where SERVER is the NetBIOS name of + the Samba server, user is the user name of + the UNIX user who owns the file, and (Long name) + is the discriptive string identifying the user (normally found in the + GECOS field of the UNIX password database). + + If the parameter nt acl support + is set to false then the file owner will + be shown as the NT user "Everyone" and the + permissions will be shown as NT "Full Control". + + + The permissions field is displayed differently for files + and directories, so I'll describe the way file permissions + are displayed first. + + + File Permissions + + The standard UNIX user/group/world triple and + the correspinding "read", "write", "execute" permissions + triples are mapped by Samba into a three element NT ACL + with the 'r', 'w', and 'x' bits mapped into the corresponding + NT permissions. The UNIX world permissions are mapped into + the global NT group Everyone, followed + by the list of permissions allowed for UNIX world. The UNIX + owner and group permissions are displayed as an NT + user icon and an NT local + group icon respectively followed by the list + of permissions allowed for the UNIX user and group. + + As many UNIX permission sets don't map into common + NT names such as "read", + "change" or "full control" then + usually the permissions will be prefixed by the words + "Special Access" in the NT display list. + + But what happens if the file has no permissions allowed + for a particular UNIX user group or world component ? In order + to allow "no permissions" to be seen and modified then Samba + overloads the NT "Take Ownership" ACL attribute + (which has no meaning in UNIX) and reports a component with + no permissions as having the NT "O" bit set. + This was chosen of course to make it look like a zero, meaning + zero permissions. More details on the decision behind this will + be given below. + + + + Directory Permissions + + Directories on an NT NTFS file system have two + different sets of permissions. The first set of permissions + is the ACL set on the directory itself, this is usually displayed + in the first set of parentheses in the normal "RW" + NT style. This first set of permissions is created by Samba in + exactly the same way as normal file permissions are, described + above, and is displayed in the same way. + + The second set of directory permissions has no real meaning + in the UNIX permissions world and represents the + "inherited" permissions that any file created within + this directory would inherit. + + Samba synthesises these inherited permissions for NT by + returning as an NT ACL the UNIX permission mode that a new file + created by Samba on this share would receive. + + + + + Modifying file or directory permissions + + Modifying file and directory permissions is as simple + as changing the displayed permissions in the dialog box, and + clicking the OK button. However, there are + limitations that a user needs to be aware of, and also interactions + with the standard Samba permission masks and mapping of DOS + attributes that need to also be taken into account. + + If the parameter nt acl support + is set to false then any attempt to set + security permissions will fail with an "Access Denied" + message. + + The first thing to note is that the "Add" + button will not return a list of users in Samba 2.0.4 (it will give + an error message of "The remote proceedure call failed + and did not execute"). This means that you can only + manipulate the current user/group/world permissions listed in + the dialog box. This actually works quite well as these are the + only permissions that UNIX actually has. + + If a permission triple (either user, group, or world) + is removed from the list of permissions in the NT dialog box, + then when the "OK" button is pressed it will + be applied as "no permissions" on the UNIX side. If you then + view the permissions again the "no permissions" entry will appear + as the NT "O" flag, as described above. This + allows you to add permissions back to a file or directory once + you have removed them from a triple component. + + As UNIX supports only the "r", "w" and "x" bits of + an NT ACL then if other NT security attributes such as "Delete + access" are selected then they will be ignored when applied on + the Samba server. + + When setting permissions on a directory the second + set of permissions (in the second set of parentheses) is + by default applied to all files within that directory. If this + is not what you want you must uncheck the "Replace + permissions on existing files" checkbox in the NT + dialog before clicking "OK". + + If you wish to remove all permissions from a + user/group/world component then you may either highlight the + component and click the "Remove" button, + or set the component to only have the special "Take + Ownership" permission (dsplayed as "O" + ) highlighted. + + + + Interaction with the standard Samba create mask + parameters + + Note that with Samba 2.0.5 there are four new parameters + to control this interaction. These are : + + security mask + force security mode + directory security mask + force directory security mode + + Once a user clicks "OK" to apply the + permissions Samba maps the given permissions into a user/group/world + r/w/x triple set, and then will check the changed permissions for a + file against the bits set in the + security mask parameter. Any bits that + were changed that are not set to '1' in this parameter are left alone + in the file permissions. + + Essentially, zero bits in the security mask + mask may be treated as a set of bits the user is not + allowed to change, and one bits are those the user is allowed to change. + + + If not set explicitly this parameter is set to the same value as + the create mask + parameter to provide compatibility with Samba 2.0.4 + where this permission change facility was introduced. To allow a user to + modify all the user/group/world permissions on a file, set this parameter + to 0777. + + Next Samba checks the changed permissions for a file against + the bits set in the + force security mode parameter. Any bits + that were changed that correspond to bits set to '1' in this parameter + are forced to be set. + + Essentially, bits set in the force security mode + parameter may be treated as a set of bits that, when + modifying security on a file, the user has always set to be 'on'. + + If not set explicitly this parameter is set to the same value + as the force + create mode parameter to provide compatibility + with Samba 2.0.4 where the permission change facility was introduced. + To allow a user to modify all the user/group/world permissions on a file, + with no restrictions set this parameter to 000. + + The security mask and force + security mode parameters are applied to the change + request in that order. + + For a directory Samba will perform the same operations as + described above for a file except using the parameter + directory security mask instead of security + mask, and force directory security mode + parameter instead of force security mode + . + + The directory security mask parameter + by default is set to the same value as the directory mask + parameter and the force directory security + mode parameter by default is set to the same value as + the force directory mode parameter to provide + compatibility with Samba 2.0.4 where the permission change facility + was introduced. + + In this way Samba enforces the permission restrictions that + an administrator can set on a Samba share, whilst still allowing users + to modify the permission bits within that restriction. + + If you want to set up a share that allows users full control + in modifying the permission bits on their files and directories and + doesn't force any particular bits to be set 'on', then set the following + parameters in the smb.conf(5) + file in that share specific section : + + security mask = 0777 + force security mode = 0 + directory security mask = 0777 + force directory security mode = 0 + + As described, in Samba 2.0.4 the parameters : + + create mask + force create mode + directory mask + force directory mode + + were used instead of the parameters discussed here. + + + + Interaction with the standard Samba file attribute + mapping + + Samba maps some of the DOS attribute bits (such as "read + only") into the UNIX permissions of a file. This means there can + be a conflict between the permission bits set via the security + dialog and the permission bits set by the file attribute mapping. + + + One way this can show up is if a file has no UNIX read access + for the owner it will show up as "read only" in the standard + file attributes tabbed dialog. Unfortunately this dialog is + the same one that contains the security info in another tab. + + What this can mean is that if the owner changes the permissions + to allow themselves read access using the security dialog, clicks + "OK" to get back to the standard attributes tab + dialog, and then clicks "OK" on that dialog, then + NT will set the file permissions back to read-only (as that is what + the attributes still say in the dialog). This means that after setting + permissions and clicking "OK" to get back to the + attributes dialog you should always hit "Cancel" + rather than "OK" to ensure that your changes + are not overridden. + + +

Viewing and changing UNIX permissions using the NT security dialogs in Samba 2.0.4

Jeremy Allison, Samba Team

12th April 1999

New in the Samba 2.0.4 release is the -ability for Windows NT clients to use their native security -settings dialog box to view and modify the underlying UNIX -permissions. -

Note that this ability is careful not to compromise the security -of the UNIX host Samba is running on, and still obeys all the -file permission rules that a Samba administrator can set. -

In Samba 2.0.4 and above the default value of the parameter -"nt acl support" has been -changed from "false" to "true", so manipulation of permissions is -turned on by default. -

How to view file security on a Samba share
------------------------------------------- -

From an NT 4.0 client, single-click with the right mouse button on -any file or directory in a Samba mounted drive letter or UNC path. -When the menu pops-up, click on the Properties entry at the -bottom of the menu. This brings up the normal file properties dialog -box, but with Samba 2.0.4 this will have a new tab along the top -marked Security. Click on this tab and you will see three buttons, -Permissions, Auditing, and Ownership. The Auditing -button will cause either an error message

"A requested privilege is
-not held by the client"

to appear if the user is not the NT Administrator, -or a dialog which is intended to allow an Administrator to add -auditing requirements to a file if the user is logged on as the -NT Administrator. This dialog is non-functional with a Samba -share at this time, as the only useful button, the Add button -will not currently allow a list of users to be seen. -

Clicking on the "Ownership" button brings up a dialog box telling -you who owns the given file. The owner name will be of the form : -

Where SERVER is the NetBIOS name of the Samba server, user -is the user name of the UNIX user who owns the file, and (Long name) -is the discriptive string identifying the user (normally found in the -GECOS field of the UNIX password database). Click on the Close -button to remove this dialog. -

If the parameter "nt acl support" -is set to "false" then the file owner will be shown as the NT user -"Everyone". -

The Take Ownership button will not allow you to change the -ownership of this file to yourself (clicking on it will display a -dialog box complaining that the user you are currently logged onto -the NT client cannot be found). The reason for this is that changing -the ownership of a file is a privilaged operation in UNIX, available -only to the root user. As clicking on this button causes NT to -attempt to change the ownership of a file to the current user logged -into the NT client this will not work with Samba at this time. -

There is an NT chown command that will work with Samba and allow -a user with Administrator privillage connected to a Samba 2.0.4 -server as root to change the ownership of files on both a local NTFS -filesystem or remote mounted NTFS or Samba drive. This is available -as part of the Seclib NT security library written by Jeremy -Allison of the Samba Team, available from the main Samba ftp site. -

Viewing file or directory permissions
-------------------------------------- -

The third button is the "Permissions" button. Clicking on this -brings up a dialog box that shows both the permissions and the UNIX -owner of the file or directory. The owner is displayed in the form : -

If the parameter "nt acl support" -is set to "false" then the file owner will be shown as the NT user -"Everyone" and the permissions will be shown as NT "Full Control". -

The permissions field is displayed differently for files and directories, -so I'll describe the way file permissions are displayed first. -

The standard UNIX user/group/world triple and the correspinding -"read", "write", "execute" permissions triples are mapped by Samba -into a three element NT ACL with the 'r', 'w', and 'x' bits mapped -into the corresponding NT permissions. The UNIX world permissions are mapped -into the global NT group Everyone, followed by the list of permissions -allowed for UNIX world. The UNIX owner and group permissions -are displayed as an NT user icon and an NT local group icon -respectively followed by the list of permissions allowed for the -UNIX user and group. -

As many UNIX permission sets don't map into common NT names such as -"read", "change" or "full control" then usually the permissions -will be prefixed by the words "Special Access" in the NT display -list. -

But what happens if the file has no permissions allowed for a -particular UNIX user group or world component ? In order to -allow "no permissions" to be seen and modified then Samba overloads -the NT "Take Ownership" ACL attribute (which has no meaning in -UNIX) and reports a component with no permissions as having the NT -"O" bit set. This was chosen of course to make it look like a -zero, meaning zero permissions. More details on the decision behind -this will be given below. -

Directories on an NT NTFS file system have two different sets of -permissions. The first set of permissions is the ACL set on the -directory itself, this is usually displayed in the first set of -parentheses in the normal "RW" NT style. This first set of -permissions is created by Samba in exactly the same way as normal -file permissions are, described above, and is displayed in the -same way. -

The second set of directory permissions has no real meaning in the -UNIX permissions world and represents the "inherited" permissions -that any file created within this directory would inherit. -

Samba synthesises these inherited permissions for NT by returning as -an NT ACL the UNIX permission mode that a new file created by Samba -on this share would receive. -

Modifying file or directory permissions
---------------------------------------- -

Modifying file and directory permissions is as simple as changing -the displayed permissions in the dialog box, and clicking the OK -button. However, there are limitations that a user needs to be aware -of, and also interactions with the standard Samba permission masks -and mapping of DOS attributes that need to also be taken into account. -

If the parameter "nt acl support" -is set to "false" then any attempt to set security permissions will -fail with an "Access Denied" message. -

The first thing to note is that the "Add" button will not return -a list of users in Samba 2.0.4 (it will give an error message of -"The remote proceedure call failed and did not execute"). This -means that you can only manipulate the current user/group/world -permissions listed in the dialog box. This actually works quite well -as these are the only permissions that UNIX actually has. -

If a permission triple (either user, group, or world) is removed from -the list of permissions in the NT dialog box, then when the "OK" -button is pressed it will be applied as "no permissions" on the UNIX -side. If you then view the permissions again the "no permissions" entry -will appear as the NT "O" flag, as described above. This allows you -to add permissions back to a file or directory once you have removed -them from a triple component. -

As UNIX supports only the "r", "w" and "x" bits of an NT ACL -then if other NT security attributes such as "Delete access" -are selected then they will be ignored when applied on the -Samba server. -

When setting permissions on a directory the second set of permissions -(in the second set of parentheses) is by default applied to all -files within that directory. If this is not what you want you -must uncheck the "Replace permissions on existing files" checkbox -in the NT dialog before clicking "OK". -

If you wish to remove all permissions from a user/group/world -component then you may either highlight the component and click -the "Remove" button, or set the component to only have the special -"Take Ownership" permission (dsplayed as "O") highlighted. -

Interaction with the standard Samba create mask parameters
----------------------------------------------------------- -

Note that with Samba 2.0.5 there are four new parameters to -control this interaction. -

security mask -force security mode -directory security mask -force directory security mode -

Once a user clicks "OK" to apply the permissions Samba maps -the given permissions into a user/group/world r/w/x triple set, -and then will check the changed permissions for a file against -the bits set in the "security mask" -parameter. Any bits that were changed that are not set to '1' -in this parameter are left alone in the file permissions. -

Essentially, zero bits in the "security mask" -mask may be treated as a set of bits the user is not allowed to change, -and one bits are those the user is allowed to change. -

If not set explicitly this parameter is set to the same value as the -"create mask" parameter to provide compatibility -with Samba 2.0.4 where this permission change facility was introduced. -To allow a user to modify all the user/group/world permissions on a file, -set this parameter to 0777. -

Next Samba checks the changed permissions for a file against the -bits set in the "force security mode" -parameter. Any bits that were changed that correspond to bits set -to '1' in this parameter are forced to be set. -

Essentially, bits set in the "force security mode" -parameter may be treated as a set of bits that, when modifying security on a file, the -user has always set to be 'on'. -

If not set explicitly this parameter is set to the same value as the -"force create mode" parameter to provide compatibility -with Samba 2.0.4 where the permission change facility was introduced. -To allow a user to modify all the user/group/world permissions on a file, -with no restrictions set this parameter to 000. -

The "directory security mask" -parameter by default is set to the same value as the "directory mask" -parameter and the "force directory security mode" -parameter by default is set to the same value as the -iurl("force directory mode")(smb.conf.5.html#forcedirectorymode) parameter -to provide compatibility with Samba 2.0.4 where the permission change facility was introduced. -

In this way Samba enforces the permission restrictions that an administrator -can set on a Samba share, whilst still allowing users to modify the -permission bits within that restriction. -

If you want to set up a share that allows users full control -in modifying the permission bits on their files and directories and -doesn't force any particular bits to be set 'on', then set the following -parameters in the smb.conf.5 file in -that share specific section : -

security mask = 0777 -force security mode = 0 -directory security mask = 0777 -force directory security mode = 0 -

Interaction with the standard Samba file attribute mapping
----------------------------------------------------------- -

Samba maps some of the DOS attribute bits (such as "read only") -into the UNIX permissions of a file. This means there can be a -conflict between the permission bits set via the security dialog -and the permission bits set by the file attribute mapping. -

One way this can show up is if a file has no UNIX read access -for the owner it will show up as "read only" in the standard -file attributes tabbed dialog. Unfortunately this dialog is -the same one that contains the security info in another tab. -

What this can mean is that if the owner changes the permissions -to allow themselves read access using the security dialog, clicks -"OK" to get back to the standard attributes tab dialog, and -then clicks "OK" on that dialog, then NT will set the file -permissions back to read-only (as that is what the attributes -still say in the dialog). This means that after setting permissions -and clicking "OK" to get back to the attributes dialog you -should always hit "Cancel" rather than "OK" to ensure -that your changes are not overridden. - - +

Jeremy Allison

Joining an NT Domain with Samba 2.2

Why is this better than security = server?

Viewing and changing UNIX permissions using the NT security dialogs in Samba 2.0.4

Jeremy Allison, Samba Team

12th April 1999

Table of Contents

Viewing and changing UNIX permissions using the NT + security dialogs

How to view file security on a Samba share

Viewing file ownership

Viewing file or directory permissions

File Permissions

Directory Permissions

Modifying file or directory permissions

Interaction with the standard Samba create mask + parameters

Interaction with the standard Samba file attribute + mapping