TracFineGrainedPermissions

Fine grained permissions¶

There is a general mechanism in place that allows custom \\permission policies\\ to grant or deny any action on any Trac resource, or even specific versions of a resource.

That mechanism is \AuthzPolicy\, an optional component in \tracopt.perm.authz_policy.\*\ which is not activated by default. It can be activated via the //Plugins// panel in the Trac administration module.

See TracPermissions for a more general introduction to Trac permissions and permission policies.

Permission Policies¶

A great diversity of permission policies can be implemented and Trac comes with a few examples.

The active policies are determined by a configuration setting:

[trac]
permission_policies = DefaultWikiPolicy,
 DefaultTicketPolicy,
 DefaultPermissionPolicy,
 LegacyAttachmentPolicy

• DefaultWikiPolicy controls readonly access to wiki pages.
• DefaultTicketPolicy provides elevated privileges in the ticket system for authenticated users.
• DefaultPermissionPolicy checks for the traditional coarse-grained permissions described in TracPermissions.
• LegacyAttachmentPolicy uses the coarse-grained permissions to check permissions on attachments.

Among the optional choices, there is #AuthzPolicy, a very generic permission policy, based on an Authz-style system. See authz_policy.py for details.

Another permission policy #AuthzSourcePolicy, uses the path-based authorization defined by Subversion to enforce permissions on the version control system.

See also sample-plugins/permissions for more examples.

AuthzPolicy¶

Configuration¶

1. modify the permission_policies option in the \trac\ section:

• Put an empty conf file (\authzpolicy.conf\) in a secure location on the server, not readable by users other than the webuser. If the file contains non-ASCII characters, the UTF-8 encoding should be used.
• Update your \trac.ini\:

[trac]
permission_policies = AuthzPolicy, DefaultWikiPolicy, DefaultTicketPolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy

1. add a new \authz_policy\ section and point the \authz_file\ option to the conf file:

[authz_policy]
authz_file = /some/trac/env/conf/authzpolicy.conf

1. enable the plugin through WebAdmin or by editing the \components\ section:

[components]
tracopt.perm.authz_policy.* = enabled

Usage Notes¶

Note the order in which permission policies are specified: policies are implemented in the sequence provided and therefore may override earlier policy specifications.

A policy will return either \True\, \False\ or \None\ for a given permission check. \True\ is returned if the policy explicitly grants the permission. \False\ is returned if the policy explicitly denies the permission. \None\ is returned if the policy is unable to either grant or deny the permission.

The \authzpolicy.conf\ file is a \.ini\ style configuration file:

[wiki:PrivatePage@*]
john = WIKI_VIEW, !WIKI_MODIFY
jack = WIKI_VIEW
* =

• Each section of the config is a glob pattern used to match against a Trac resource descriptor. These descriptors are in the form:

<realm>:<id>@<version>[/<realm>:<id>@<version> ...]

Resources are ordered left to right, from parent to child. If any component is inapplicable, \\*\ is substituted. If the version pattern is not specified explicitly, all versions (\@\*\) is added implicitly. Example: Match the WikiStart page:

[wiki:*]
[wiki:WikiStart*]
[wiki:WikiStart@*]
[wiki:WikiStart]

Example: Match the attachment \wiki:[WikiStart](/briareus/notes/WikiStart/)@117/attachment:FOO.JPG@\*\ on WikiStart:

[wiki:*]
[wiki:WikiStart*]
[wiki:WikiStart@*]
[wiki:WikiStart@*/attachment:*]
[wiki:WikiStart@117/attachment:FOO.JPG]

• Sections are checked against the current Trac resource descriptor IN ORDER of appearance in the configuration file. ORDER IS CRITICAL.

• If a key (username) is prefixed with a \@\, it is treated as a group.
• If a value (permission) is prefixed with a \\!\, the permission is denied rather than granted.

• Once a section matches, the current username is matched against the keys (usernames) of the section, IN ORDER.

The username will match any of 'anonymous', 'authenticated', or '*', using normal Trac permission rules.

For example, if the \authz_file\ contains:

[wiki:WikiStart@*]
* = WIKI_VIEW

[wiki:PrivatePage@*]
john = WIKI_VIEW
* = !WIKI_VIEW

and the default permissions are set like this:

john           WIKI_VIEW
jack           WIKI_VIEW
# anonymous has no WIKI_VIEW

Then:

• All versions of WikiStart will be viewable by everybody, including anonymous
• PrivatePage will be viewable only by john
• other pages will be viewable only by john and jack

Groups:

[groups]
admins = john, jack
devs = alice, bob

[wiki:Dev@*]
@admins = TRAC_ADMIN
@devs = WIKI_VIEW
* =

[*]
@admins = TRAC_ADMIN
* =

Then:

• everything is blocked (whitelist approach), but
• admins get all TRAC_ADMIN everywhere and
• devs can view wiki pages.

Some repository examples (Browse Source specific):

# A single repository:
[repository:test_repo@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW for the entire test_repo

# The default repository (requires Trac 1.0.2 or later):
[repository:@*]
john = BROWSER_VIEW, FILE_VIEW
# John has BROWSER_VIEW and FILE_VIEW for the entire default repository

# All repositories:
[repository:*@*]
jack = BROWSER_VIEW, FILE_VIEW
# Jack has BROWSER_VIEW and FILE_VIEW for all repositories

Very granular repository access:

# John has BROWSER_VIEW and FILE_VIEW access to trunk/src/some/location/ only
[repository:test_repo@*/source:trunk/src/some/location/*@*]
john = BROWSER_VIEW, FILE_VIEW

# John has BROWSER_VIEW and FILE_VIEW access to only revision 1 of all files at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/*@1]
john = BROWSER_VIEW, FILE_VIEW

# John has BROWSER_VIEW and FILE_VIEW access to all revisions of 'somefile' at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/somefile@*]
john = BROWSER_VIEW, FILE_VIEW

# John has BROWSER_VIEW and FILE_VIEW access to only revision 1 of 'somefile' at trunk/src/some/location only
[repository:test_repo@*/source:trunk/src/some/location/somefile@1]
john = BROWSER_VIEW, FILE_VIEW

Missing Features¶

Although possible with the DefaultPermissionPolicy handling (see Admin panel), fine-grained permissions still miss those grouping features (see trac:#9573, trac:#5648). Patches are partially available, see authz_policy.2.patch, part of #6680.

You cannot do the following:

[groups]
team1 = a, b, c
team2 = d, e, f
team3 = g, h, i
departmentA = team1, team2

Permission groups are not supported either, so you cannot do the following:

[groups]
permission_level_1 = WIKI_VIEW, TICKET_VIEW
permission_level_2  = permission_level_1, WIKI_MODIFY, TICKET_MODIFY
[*]
@team1 = permission_level_1
@team2 = permission_level_2
@team3 = permission_level_2, TICKET_CREATE

AuthzSourcePolicy (\mod_authz_svn\-like permission policy) #AuthzSourcePolicy¶

\AuthzSourcePolicy\ can be used for restricting access to the repository. Granular permission control needs a definition file, which is the one used by Subversion's \mod_authz_svn\. More information about this file format and about its usage in Subversion is available in the Path-Based Authorization section in the Server Configuration chapter of the svn book.

Example:

[/]
* = r

[/branches/calc/bug-142]
harry = rw
sally = r

[/branches/calc/bug-142/secret]
harry =

• / = Everyone has read access by default
• /branches/calc/bug-142 = harry has read/write access, sally read only
• /branches/calc/bug-142/secret = harry has no access, sally has read access (inherited as a sub folder permission)

Trac Configuration¶

To activate granular permissions you must specify the authz_file option in the \svn\ section of trac.ini. If this option is set to null or not specified, the permissions will not be used.

[svn]
authz_file = /path/to/svnaccessfile

If you want to support the use of the \`''modulename'':/''some''/''path''\ syntax within the \authz_file`, add:

authz_module_name = modulename

where modulename refers to the same repository indicated by the \<name>.dir\ entry in the \repositories\ section. As an example, if the \somemodule.dir\ entry in the \repositories\ section is \/srv/active/svn/somemodule\, that would yield the following:

[svn]
authz_file = /path/to/svnaccessfile
authz_module_name = somemodule
...
[repositories]
somemodule.dir = /srv/active/svn/somemodule

where the svn access file, /path/to/svnaccessfile, contains entries such as [somemodule:/some/path].

Make sure you have AuthzSourcePolicy included in the permission_policies list in trac.ini, otherwise the authz permissions file will be ignored.

[trac]
permission_policies = AuthzSourcePolicy, DefaultWikiPolicy, DefaultTicketPolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy

Subversion Configuration¶

The same access file is typically applied to the corresponding Subversion repository using an Apache directive like this:

<Location /repos>
  DAV svn
  SVNParentPath /usr/local/svn

  # our access control policy
  AuthzSVNAccessFile /path/to/svnaccessfile
</Location>

For information about how to restrict access to entire projects in a multiple project environment see trac:wiki:TracMultipleProjectsSVNAccess.

DefaultWikiPolicy and DefaultTicketPolicy¶

Since 1.1.2, the read-only attribute of wiki pages is enabled and enforced when \DefaultWikiPolicy\ is in the list of active permission policies (\DefaultWikiPolicy\ was named \ReadonlyWikiPolicy\ from Trac 1.1.2 to 1.3.1). The default for new Trac installations in 1.3.2 and later is:

[trac]
permission_policies = DefaultWikiPolicy,
 DefaultTicketPolicy,
 DefaultPermissionPolicy,
 LegacyAttachmentPolicy

\DefaultWikiPolicy\ returns \False\ to deny modify, delete and rename actions on wiki pages when the page has the read-only attribute set and the user does not have \WIKI_ADMIN\, regardless of \WIKI_MODIFY\, \WIKI_DELETE\ and \WIKI_RENAME\ permissions. It returns \None\ for all other cases, which causes the next permission policy in the list to be consulted.

Since 1.3.2 \DefaultTicketPolicy\ implements the following behaviors:

• Authenticated user can edit their own comments.
• Authenticated user with \TICKET_APPEND\ or \TICKET_CHGPROP\ can modify the description of a ticket they reported.
• User with \MILESTONE_VIEW\ can change the ticket milestone.

The wiki- and ticket-specific behaviors are implemented in permission policies so they can be easily replaced in case other behavior is desired.

When upgrading from earlier versions of Trac, \DefaultWikiPolicy, DefaultTicketPolicy\ will be appended to the list of \permission_policies\ when upgrading the environment, provided that \permission_policies\ has the default value (\ReadonlyWikiPolicy, DefaultPermissionPolicy, LegacyAttachmentPolicy\ if upgrading from Trac 1.1.2 or later). If any non-default \permission_polices\ are active, \DefaultWikiPolicy, DefaultTicketPolicy\ \\will need to be manually added\\ to the list. A message will be echoed to the console when upgrading the environment, indicating if any action needs to be taken.

\\DefaultWikiPolicy and DefaultTicketPolicy must be listed //before// DefaultPermissionPolicy\\. The latter returns \True\ to allow modify, delete or rename actions when the user has the respective \WIKI_\*\ permission, without consideration for the read-only attribute. Similarly, some of the behaviors implemented in \DefaultTicketPolicy\ won't be considered if \DefaultPermissionPolicy\ is executed first.

When active, the #AuthzPolicy should therefore come before \DefaultWikiPolicy, DefaultTicketPolicy\, allowing it to grant or deny the actions on individual resources, which is the usual ordering for \AuthzPolicy\ in the \permission_policies\ list.

[trac]
permission_policies = AuthzPolicy,
 DefaultWikiPolicy,
 DefaultTicketPolicy,
 DefaultPermissionPolicy,
 LegacyAttachmentPolicy

The placement of #AuthzSourcePolicy relative to \DefaultWikiPolicy, DefaultTicketPolicy\ does not matter since they don't perform checks on the same realms.

For all other permission policies, the user will need to decide the proper ordering. Generally, if the permission policy should be capable of overriding the checks performed by \DefaultWikiPolicy\ or \DefaultTicketPolicy\, it should come before the policy it overrides. If \DefaultWikiPolicy\ or \DefaultTicketPolicy\ should override the check performed by another permission policy, as is the case for those policies relative to \DefaultPermissionPolicy\, then the overriding policy should come first.

Debugging permissions¶

In trac.ini set:

[logging]
log_file = trac.log
log_level = DEBUG
log_type = file

Display the trac.log to understand what checks are being performed:

tail -n 0 -f log/trac.log | egrep '\[perm\]|\[authz_policy\]'

See the sourced documentation of the plugin for more info.

See also: TracPermissions, FineGrainedPageAuthzEditorPlugin for a simple editor.