Solaris ACL Model

Previous versions of Solaris supported an ACL implementation that was primarily based on the POSIX-draft ACL specification. The POSIX-draft based ACLs are used to protect UFS files and are translated by versions of NFS prior to NFSv4.

With the introduction of NFSv4, a new ACL model fully supports the interoperability that NFSv4 offers between UNIX and non-UNIX clients. The new ACL implementation, as defined in the NFSv4 specification, provides much richer semantics that are based on NT-style ACLs.

The main differences of the new ACL model are as follows:

Based on the NFSv4 specification and similar to NT-style ACLs.
Provide much more granular set of access privileges. For more information, see Table 7-2.
Set and displayed with the chmod and ls commands rather than the setfacl and getfacl commands.
Provide richer inheritance semantics for designating how access privileges are applied from directory to subdirectories, and so on. For more information, see ACL Inheritance.

Both ACL models provide more fine-grained access control than is available with the standard file permissions. Much like POSIX-draft ACLs, the new ACLs are composed of multiple Access Control Entries (ACEs).

POSIX-draft style ACLs use a single entry to define what permissions are allowed and what permissions are denied. The new ACL model has two types of ACEs that affect access checking: ALLOW and DENY. As such, you cannot infer from any single ACE that defines a set of permissions whether or not the permissions that weren't defined in that ACE are allowed or denied.

Translation between NFSv4-style ACLs and POSIX-draft ACLs is as follows:

If you use any ACL-aware utility, such as the cp, mv, tar, cpio, or rcp commands, to transfer UFS files with ACLs to a ZFS file system, the POSIX-draft ACLs are translated into the equivalent NFSv4-style ACLs.
Some NFSv4-style ACLs are translated to POSIX-draft ACLs. You see a message similar to the following if an NFSv4–style ACL isn't translated to a POSIX-draft ACL:
```
# cp -p filea /var/tmp
cp: failed to set acl entries on /var/tmp/filea
```
If you create a UFS tar or cpio archive with the preserve ACL option (tar -p or cpio -P) on a system that runs a current Solaris release, you will lose the ACLs when the archive is extracted on a system that runs a previous Solaris release.

All of the files are extracted with the correct file modes, but the ACL entries are ignored.
You can use the ufsrestore command to restore data into a ZFS file system. If the original data includes POSIX-style ACLs, they are converted to NFSv4-style ACLs.
If you attempt to set an NFSv4-style ACL on a UFS file, you see a message similar to the following:
```
chmod: ERROR: ACL type's are different
```

If you attempt to set a POSIX-style ACL on a ZFS file, you will see messages similar to the following:

# getfacl filea
File system doesn't support aclent_t style ACL's.
See acl(5) for more information on Solaris ACL support.

For information about other limitations with ACLs and backup products, see Saving ZFS Data With Other Backup Products.

Syntax Descriptions for Setting ACLs

Two basic ACL formats are provided as follows:

Trivial ACL – Contains only traditional UNIX user, group, and owner entries.
Non-Trivial ACL – Contains more entries than just owner, group, and everyone, or includes inheritance flags set, or the entries are ordered in a non-traditional way.

Syntax for Setting Trivial ACLs

chmod [options] A[index]{+|=}owner@ |group@ |everyone@:access-permissions/...[:inheritance-flags]:deny | allow file

chmod [options] A-owner@, group@, everyone@:access-permissions/...[:inheritance-flags]:deny | allow file ...

chmod [options] A[index]- file

Syntax for Setting Non-Trivial ACLs

chmod [options] A[index]{+|=}user|group:name:access-permissions/...[:inheritance-flags]:deny | allow file

chmod [options] A-user|group:name:access-permissions/...[:inheritance-flags]:deny | allow file ...

chmod [options] A[index]- file

owner@, group@, everyone@: Identifies the ACL-entry-type for trivial ACL syntax. For a description of ACL-entry-types, see Table 7-1.
user or group:ACL-entry-ID=username or groupname: Identifies the ACL-entry-type for explicit ACL syntax. The user and group ACL-entry-type must also contain the ACL-entry-ID, username or groupname. For a description of ACL-entry-types, see Table 7-1.
access-permissions/.../: Identifies the access permissions that are granted or denied. For a description of ACL access privileges, see Table 7-2.
inheritance-flags: Identifies an optional list of ACL inheritance flags. For a description of the ACL inheritance flags, see Table 7-4.
deny | allow: Identifies whether the access permissions are granted or denied.

In the following example, no ACL-entry-ID value exists for owner@, group@, or everyone@..

group@:write_data/append_data/execute:deny

The following example includes an ACL-entry-ID because a specific user (ACL-entry-type) is included in the ACL.

0:user:gozer:list_directory/read_data/execute:allow

When an ACL entry is displayed, it looks similar to the following:

2:group@:write_data/append_data/execute:deny

The 2 or the index-ID designation in this example identifies the ACL entry in the larger ACL, which might have multiple entries for owner, specific UIDs, group, and everyone. You can specify the index-ID with the chmod command to identify which part of the ACL you want to modify. For example, you can identify index ID 3 as A3 to the chmod command, similar to the following:

chmod A3=user:venkman:read_acl:allow filename

ACL entry types, which are the ACL representations of owner, group, and other, are described in the following table.

Table 7-1 ACL Entry Types

ACL Entry Type	Description
`owner@`	Specifies the access granted to the owner of the object.
`group@`	Specifies the access granted to the owning group of the object.
`everyone@`	Specifies the access granted to any user or group that does not match any other ACL entry.
`user`	With a user name, specifies the access granted to an additional user of the object. Must include the ACL-entry-ID, which contains a `username` or `userID`. If the value is not a valid numeric UID or `username`, the ACL entry type is invalid.
`group`	With a group name, specifies the access granted to an additional group of the object. Must include the ACL-entry-ID, which contains a `groupname` or `groupID`. If the value is not a valid numeric GID or `groupname`, the ACL entry type is invalid.

ACL access privileges are described in the following table.

Table 7-2 ACL Access Privileges

Access Privilege	Compact Access Privilege	Description
`add_file`	`w`	Permission to add a new file to a directory.
`add_subdirectory`	`p`	On a directory, permission to create a subdirectory.
`append_data`	`p`	Not currently implemented.
`delete`	`d`	Permission to delete a file. For more information about specific `delete` permission behavior, see Table 7-3.
`delete_child`	`D`	Permission to delete a file or directory within a directory. For more information about specific `delete_child` permission behavior, see Table 7-3.
`execute`	`x`	Permission to execute a file or search the contents of a directory.
`list_directory`	`r`	Permission to list the contents of a directory.
`read_acl`	`c`	Permission to read the ACL (`ls`).
`read_attributes`	a	Permission to read basic attributes (non-ACLs) of a file. Think of basic attributes as the stat level attributes. Allowing this access mask bit means the entity can execute `ls`(1) and `stat`(2).
`read_data`	`r`	Permission to read the contents of the file.
`read_xattr`	`R`	Permission to read the extended attributes of a file or perform a lookup in the file's extended attributes directory.
`synchronize`	`s`	Not currently implemented.
`write_xattr`	`W`	Permission to create extended attributes or write to the extended attributes directory. Granting this permission to a user means that the user can create an extended attribute directory for a file. The attribute file's permissions control the user's access to the attribute.
`write_data`	`w`	Permission to modify or replace the contents of a file.
`write_attributes`	`A`	Permission to change the times associated with a file or directory to an arbitrary value.
`write_acl`	`C`	Permission to write the ACL or the ability to modify the ACL by using the `chmod` command.
`write_owner`	`o`	Permission to change the file's owner or group. Or, the ability to execute the `chown` or `chgrp` commands on the file. Permission to take ownership of a file or permission to change the group ownership of the file to a group of which the user is a member. If you want to change the file or group ownership to an arbitrary user or group, then the `PRIV_FILE_CHOWN` privilege is required.

The following table provides additional details about ACL delete and delete_child behavior.

Table 7-3 ACL delete and delete_child Permission Behavior

Parent Directory Permissions	Target Object Permissions
	ACL allows delete	ACL denies delete	Delete permission unspecified
ACL allows `delete_child`	Permit	Permit	Permit
ACL denies `delete_child`	Permit	Deny	Deny
ACL allows only `write` and `execute`	Permit	Permit	Permit
ACL denies `write` and `execute`	Permit	Deny	Deny

ZFS ACL Sets

The following ACL combinations can be applied in an ACL set rather than setting individual permissions separately. The following ACL sets are available.

ACL Set Name	Included ACL Permissions
`full_set`	All permissions
`modify_set`	all permissions except `write_acl` and `write_owner`
`read_set`	`read_data`, `read_attributes`, `read_xattr`, and `read_acl`
`write_set`	`write_data`, `append_data`, `write_attributes`, and `write_xattr`

These ACL sets are prefined and cannot be modified.

ACL Inheritance

The purpose of using ACL inheritance is so that a newly created file or directory can inherit the ACLs they are intended to inherit, but without disregarding the existing permission bits on the parent directory.

By default, ACLs are not propagated. If you set a non-trivial ACL on a directory, it is not inherited to any subsequent directory. You must specify the inheritance of an ACL on a file or directory.

The optional inheritance flags are described in the following table.

Table 7-4 ACL Inheritance Flags

Inheritance Flag	Compact Inheritance Flag	Description
`file_inherit`	`f`	Only inherit the ACL from the parent directory to the directory's files.
`dir_inherit`	`d`	Only inherit the ACL from the parent directory to the directory's subdirectories.
`inherit_only`	`i`	Inherit the ACL from the parent directory but applies only to newly created files or subdirectories and not the directory itself. This flag requires the `file_inherit` flag, the `dir_inherit` flag, or both, to indicate what to inherit.
`no_propagate`	`n`	Only inherit the ACL from the parent directory to the first-level contents of the directory, not the second-level or subsequent contents. This flag requires the `file_inherit` flag, the `dir_inherit` flag, or both, to indicate what to inherit.
`-`	N/A	No permission granted.
Currently, the following flags are only applicable to a SMB client or server.
`successful_access`	`S`	Indicates whether an alarm or audit record should be initiated upon a successful access. This flag is used with audit or alarm ACE types.
`failed_access`	`F`	Indicates whether an alarm or audit record should be initiated when an access fails. This flag is used with audit or alarm ACE types.
`inherited`	`I`	Indicates that an ACE was inherited.

In addition, you can set a default ACL inheritance policy on the file system that is more strict or less strict by using the aclinherit file system property. For more information, see the next section.

ACL Properties

The ZFS file system includes the following ACL properties to determine the specific behavior of ACL inheritance and ACL interaction with chmod operations.

aclinherit – Determine the behavior of ACL inheritance. Values include the following:
- discard – For new objects, no ACL entries are inherited when a file or directory is created. The ACL on the file or directory is equal to the permission mode of the file or directory.
- noallow – For new objects, only inheritable ACL entries that have an access type of deny are inherited.
- restricted – For new objects, the write_owner and write_acl permissions are removed when an ACL entry is inherited.
- passthrough – When property value is set to passthrough, files are created with a mode determined by the inheritable ACEs. If no inheritable ACEs exist that affect the mode, then the mode is set in accordance to the requested mode from the application.
- passthrough-x – Has the same semantics as passthrough, except that when passthrough-x is enabled, files are created with the execute (x) permission, but only if execute permission is set in the file creation mode and in an inheritable ACE that affects the mode.
The default mode for the aclinherit is restricted.
aclmode – Modifies ACL behavior when a file is initially created or controls how an ACL is modified during a chmod operation. Values include the following:
- discard – A file system with an aclmode property of discard deletes all ACL entries that do not represent the mode of the file. This is the default value.
- mask – A file system with an aclmode property of mask reduces user or group permissions. The permissions are reduced, such that they are no greater than the group permission bits, unless it is a user entry that has the same UID as the owner of the file or directory. In this case, the ACL permissions are reduced so that they are no greater than owner permission bits. The mask value also preserves the ACL across mode changes, provided an explicit ACL set operation has not been performed.
- passthrough – A file system with an aclmode property of passthrough indicates that no changes are made to the ACL other than generating the necessary ACL entries to represent the new mode of the file or directory.
The default mode for the aclmode is discard.

For more information on using the aclmode property, see Example 7-14.

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