Gerrit Code Review - Access Controls

Access controls in Gerrit are group based. Every user account is a member of one or more groups, and access and privileges are granted to those groups. Access rights cannot be granted to individual users.

System Groups

Gerrit comes with the following system groups:

• Anonymous Users

• Change Owner

• Project Owners

• Registered Users

The system groups are assigned special access and membership management privileges.

Anonymous Users

All users are automatically a member of this group. Users who are not signed in are a member of only this group, and no others.

Any access rights assigned to this group are inherited by all users.

Administrators and project owners can grant access rights to this group in order to permit anonymous users to view project changes, without requiring sign in first. Currently it is only worthwhile to grant Read access to this group as Gerrit requires an account identity for all other operations.

Project Owners

Access rights assigned to this group are always evaluated within the context of a project to which the access rights apply. These rights therefore apply to all the users who are owners of this project.

By assigning access rights to this group on a parent project Gerrit administrators can define a set of default access rights for project owners. Child projects inherit these access rights where they are resolved to the users that own the child project. Having default access rights for project owners assigned on a parent project may avoid the need to initially configure access rights for newly created child projects.

Change Owner

Access rights assigned to this group are always evaluated within the context of a change to which the access rights apply. These rights therefore apply to the user who is the owner of this change.

It is typical to assign a label to this group, allowing the change owner to vote on his change, but not actually cause it to become approved or rejected.

Registered Users

All signed-in users are automatically a member of this group (and also Anonymous Users, see above).

Any access rights assigned to this group are inherited by all users as soon as they sign-in to Gerrit. If OpenID authentication is being employed, moving from only Anonymous Users into this group is very easy. Caution should be taken when assigning any permissions to this group.

It is typical to assign Code-Review -1..+1 to this group, allowing signed-in users to vote on a change, but not actually cause it to become approved or rejected.

Registered users are always permitted to make and publish comments on any change in any project they have Read access to.

Predefined Groups

Predefined groups differs from system groups by the fact that they exist in the ACCOUNT_GROUPS table (like normal groups) but predefined groups are created on Gerrit site initialization and unique UUIDs are assigned to those groups. These UUIDs are different on different Gerrit sites.

Gerrit comes with two predefined groups:

• Administrators

• Non-Interactive Users

Administrators

This is a predefined group, created on Gerrit site initialization, that has the capability Administrate Server assigned.

It is a normal Gerrit group without magic. This means if you remove the Administrate Server capability from it, its members are no longer Gerrit administrators, despite the group name. The group may also be renamed.

Non-Interactive Users

This is the Gerrit “batch” identity. The capabilities Priority BATCH and Stream Events are assigned to this predefined group on Gerrit site creation.

The members of this group are not expected to perform interactive operations on the Gerrit web front-end.

However, sometimes such a user may need a separate thread pool in order to prevent it from grabbing threads from the interactive users.

These users live in a second thread pool, which separates operations made by the non-interactive users from the ones made by the interactive users. This ensures that the interactive users can keep working when resources are tight.

Account Groups

Account groups contain a list of zero or more user account members, added individually by a group owner. Any user account listed as a group member is given any access rights granted to the group.

Every group has one other group designated as its owner. Users who are members of the owner group can:

• Add users and other groups to this group

• Remove users and other groups from this group

• Change the name of this group

• Change the description of this group

• Change the owner of this group, to another group

It is permissible for a group to own itself, allowing the group members to directly manage who their peers are.

Newly created groups are automatically created as owning themselves, with the creating user as the only member. This permits the group creator to add additional members, and change the owner to another group if desired.

It is somewhat common to create two groups at the same time, for example Foo and Foo-admin, where the latter group Foo-admin owns both itself and also group Foo. Users who are members of Foo-admin can thus control the membership of Foo, without actually having the access rights granted to Foo. This configuration can help prevent accidental submits when the members of Foo have submit rights on a project, and the members of Foo-admin typically do not need to have such rights.

LDAP Groups

LDAP groups are Account Groups that are maintained inside of your LDAP instance. If you are using LDAP to manage your groups they will not appear in the Groups list. However you can use them just like regular Account Groups by prefixing your group with “ldap/” in the Access Control for a project. For example “ldap/foo-project” will add the LDAP “foo-project” group to the access list.

Project Access Control Lists

A system wide access control list affecting all projects is stored in project “All-Projects”. This inheritance can be configured through gerrit set-project-parent.

Per-project access control lists are also supported.

Users are permitted to use the maximum range granted to any of their groups on a label. For example, a user is a member of Foo Leads, and the following ACLs are granted on a project:

Then the effective range permitted to be used by the user is -2..+2, as the user is a member of all three groups (see above about the system groups) and the maximum range is chosen (so the lowest value granted to any group, and the highest value granted to any group).

Reference-level access control is also possible.

Permissions can be set on a single reference name to match one branch (e.g. refs/heads/master), or on a reference namespace (e.g. +refs/heads/*+) to match any branch starting with that prefix. So a permission with +refs/heads/*+ will match all of refs/heads/master, refs/heads/experimental, refs/heads/release/1.0 etc.

Reference names can also be described with a regular expression by prefixing the reference name with ^. For example ^refs/heads/[a-z]{1,8} matches all lower case branch names between 1 and 8 characters long. Within a regular expression . is a wildcard matching any character, but may be escaped as \.. The dk.brics.automaton library is used for evaluation of regular expression access control rules. See the library documentation for details on this particular regular expression flavor. One quirk is that the shortest possible pattern expansion must be a valid ref name: thus ^refs/heads/.*/name will fail because refs/heads//name is not a valid reference, but ^refs/heads/.+/name will work.

References can have the user name or the sharded account ID of the current user automatically included, creating dynamic access controls that change to match the currently logged in user. For example to provide a personal sandbox space to all developers, +refs/heads/sandbox/${username}/*+ allows the user joe to use refs/heads/sandbox/joe/foo. The sharded account ID can be used to give users access to their user branch in the All-Users repository, for example +refs/users/${shardeduserid}+ is resolved to refs/users/23/1011123 if the account ID of the current user is 1011123.

When evaluating a reference-level access right, Gerrit will use the full set of access rights to determine if the user is allowed to perform a given action. For example, if a user is a member of Foo Leads, they are reviewing a change destined for the refs/heads/qa branch, and the following ACLs are granted on the project:

Then the effective range permitted to be used by the user is -2..+2, as the user’s membership of Foo Leads effectively grant them access to the entire reference space, thanks to the wildcard.

Gerrit also supports exclusive reference-level access control.

It is possible to configure Gerrit to grant an exclusive ref level access control so that only users of a specific group can perform an operation on a project/reference pair. This is done by ticking the exclusive flag when setting the permission for the refs/heads/qa branch.

For example, if a user who is a member of Foo Leads tries to review a change destined for branch refs/heads/qa in a project, and the following ACLs are granted:

Then this user will not have Code-Review rights on that change, since there is an exclusive access right in place for the refs/heads/qa branch. This allows locking down access for a particular branch to a limited set of users, bypassing inherited rights and wildcards.

In order to grant the ability to Code-Review to the members of Foo Leads, in refs/heads/qa then the following access rights would be needed:

OpenID Authentication

If the Gerrit instance is configured to use OpenID authentication, an account’s effective group membership will be restricted to only the Anonymous Users and Registered Users groups, unless all of its OpenID identities match one or more of the patterns listed in the auth.trustedOpenID list from gerrit.config.

All Projects

Any access right granted to a group within All-Projects is automatically inherited by every other project in the same Gerrit instance. These rights can be seen, but not modified, in any other project’s Access administration tab.

Only members of the groups with the Administrate Server capability may edit the access control list for All-Projects. By default this capability is given to the group Administrators, but can be given to more groups.

Ownership of this project cannot be delegated to another group. This restriction is by design. Granting ownership to another group gives nearly the same level of access as membership in Administrators does, as group members would be able to alter permissions for every managed project including global capabilities.

Per-Project

The per-project ACL is evaluated before the global All-Projects ACL, permitting some limited override capability to project owners. This behavior is generally only useful on the Read category when granting DENY within a specific project to deny a group access.

Special and magic references

The reference namespaces used in git are generally two, one for branches and one for tags:

• refs/heads/*

• refs/tags/*

However, every reference under refs/* is really available, and in Gerrit this opportunity for giving other refs a special meaning is used. In Gerrit they are sometimes used as magic/virtual references that give the push to Gerrit a special meaning.

Special references

The special references have content that’s either generated by Gerrit or contains important project configuration that Gerrit needs. When making changes to these references, Gerrit will take extra precautions to verify the contents compatibility at upload time.

refs/changes/*

Under this namespace each uploaded patch set for every change gets a static reference in their git. The format is convenient but still intended to scale to hundreds of thousands of patch sets. To access a given patch set you will need the change number and patch set number.

refs/changes/<last two digits of change number>/ <change number>/ <patch set number>

You can also find these static references linked on the page of each change.

refs/meta/config

This is where the Gerrit configuration of each project resides. This branch contains several files of importance: project.config, groups and rules.pl. Together they control access and behavior during the change review process.

refs/meta/dashboards/*

There’s a dedicated page where you can read more about User Dashboards.

refs/notes/review

Autogenerated copy of review notes for all changes in the git. Each log entry on the refs/notes/review branch also references the patch set on which the review is made. This functionality is provided by the review-notes plugin.

Magic references

These are references with added functionality to them compared to a regular git push operation.

refs/for/<branch ref>

Most prominent is the refs/for/<branch ref> reference which is the reference upon which we build the code review intercept before submitting a commit to the branch it’s uploaded to.

Further documentation on how to push can be found on the Upload changes page.

Access Categories

Gerrit has several permission categories that can be granted to groups within projects, enabling functionality for that group’s members.

Abandon

This category controls whether users are allowed to abandon changes to projects in Gerrit. It can give permission to abandon a specific change to a given ref.

The uploader of a change, anyone granted the Owner permission at the ref or project level, and anyone granted the Administrate Server permission can also Abandon changes.

This also grants the permission to restore a change if the user also has push permission on the change’s destination ref.

Create Reference

The create reference category controls whether it is possible to create new references, branches or tags. This implies that the reference must not already exist, it’s not a destructive permission in that you can’t overwrite or remove any previously existing references (and also discard any commits in the process).

It’s probably most common to either permit the creation of a single branch in many gits (by granting permission on a parent project), or to grant this permission to a name pattern of branches.

This permission is often given in conjunction with regular push branch permissions, allowing the holder of both to create new branches as well as bypass review for new commits on that branch.

To push lightweight (non-annotated) tags, grant Create Reference for reference name +refs/tags/*+, as lightweight tags are implemented just like branches in Git. To push a lightweight tag on a new commit (commit not reachable from any branch/tag) grant Push permission on +refs/tags/*+ too. The Push permission on +refs/tags/*+ also allows fast-forwarding of lightweight tags.

For example, to grant the possibility to create new branches under the namespace foo, you have to grant this permission on +refs/heads/foo/*+ for the group that should have it. Finally, if you plan to grant each user a personal namespace in where they are free to create as many branches as they wish, you should grant the create reference permission so it’s possible to create new branches. This is done by using the special ${username} keyword in the reference pattern, e.g. +refs/heads/sandbox/${username}/*+. If you do, it’s also recommended you grant the users the push force permission to be able to clean up stale branches.

Delete Reference

The delete reference category controls whether it is possible to delete references, branches or tags. It doesn’t allow any other update of references.

Deletion of references is also possible if Push with the force option is granted, however that includes the permission to fast-forward and force-update references to existing and new commits. Being able to push references for new commits is bad if bypassing of code review must be prevented.

Forge Author

Normally Gerrit requires the author and the committer identity lines in a Git commit object (or tagger line in an annotated tag) to match one of the registered email addresses of the uploading user. This permission allows users to bypass parts of that validation, which may be necessary when mirroring changes from an upstream project.

Permits the use of an unverified author line in commit objects. This can be useful when applying patches received by email from 3rd parties, when cherry-picking changes written by others across branches, or when amending someone else’s commit to fix up a minor problem before submitting.

By default this is granted to Registered Users in all projects, but a site administrator may disable it if verified authorship is required.

Forge Committer

Normally Gerrit requires the author and the committer identity lines in a Git commit object (or tagger line in an annotated tag) to match one of the registered email addresses of the uploading user. This permission allows users to bypass parts of that validation, which may be necessary when mirroring changes from an upstream project.

Allows the use of an unverified committer line in commit objects, or an unverified tagger line in annotated tag objects. Typically this is only required when mirroring commits from an upstream project repository.

Forge Server

Normally Gerrit requires the author and the committer identity lines in a Git commit object (or tagger line in an annotated tag) to match one of the registered email addresses of the uploading user. This permission allows users to bypass parts of that validation, which may be necessary when mirroring changes from an upstream project.

Allows the use of the server’s own name and email on the committer line of a new commit object. This should only be necessary when force pushing a commit history which has been rewritten by git filter-branch and that contains merge commits previously created by this Gerrit Code Review server.

Owner

The Owner category controls which groups can modify the project’s configuration. Users who are members of an owner group can:

• Change the project description

• Grant/revoke any access rights, including Owner

To get SSH branch access project owners must grant an access right to a group they are a member of, just like for any other user.

Ownership over a particular branch subspace may be delegated by entering a branch pattern. To delegate control over all branches that begin with qa/ to the QA group, add Owner category for reference +refs/heads/qa/*+. Members of the QA group can further refine access, but only for references that begin with refs/heads/qa/. See project owners to find out more about this role.

For the All-Projects root project any Owner access right on refs/* is ignored since this permission would allow users to edit the global capabilities, which is the same as being able to administrate the Gerrit server (e.g. the user could assign the Administrate Server capability to the own account).

Push

This category controls how users are allowed to upload new commits to projects in Gerrit. It can either give permission to push directly into a branch, bypassing any code review process that would otherwise be used. Or it may give permission to upload new changes for code review, this depends on which namespace the permission is granted to.

Direct Push

Any existing branch can be fast-forwarded to a new commit. Creation of new branches is controlled by the Create Reference category. Deletion of existing branches is rejected. This is the safest mode as commits cannot be discarded.

• Force option

  Allows an existing branch to be deleted. Since a force push is effectively a delete immediately followed by a create, but performed atomically on the server and logged, this option also permits forced push updates to branches. Enabling this option allows existing commits to be discarded from a project history.

The push category is primarily useful for projects that only want to take advantage of Gerrit’s access control features and do not need its code review functionality. Projects that need to require code reviews should not grant this category.

Upload To Code Review

The Push access right granted on the namespace refs/for/refs/heads/BRANCH permits the user to upload a non-merge commit to the project’s refs/for/BRANCH namespace, creating a new change for code review.

A user must be able to clone or fetch the project in order to create a new commit on their local system, so in practice they must also have the Read access granted to upload a change.

For an open source, public Gerrit installation, it is common to grant Push for +refs/for/refs/heads/*+ to Registered Users in the All-Projects ACL. For more private installations, its common to grant Push for +refs/for/refs/heads/*+ to all users of a project.

• Force option

  The force option has no function when granted to a branch in the +refs/for/refs/heads/*+ namespace.

Add Patch Set

This category controls which users are allowed to upload new patch sets to existing changes. Irrespective of this permission, change owners are always allowed to upload new patch sets for their changes. This permission needs to be set on refs/for/*.

By default, this permission is granted to Registered Users on refs/for/*, allowing all registered users to upload a new patch set to any change. Revoking this permission (by granting it to no groups and setting the “Exclusive” flag) will prevent users from uploading a patch set to a change they do not own.

Push Merge Commits

The Push Merge Commit access right permits the user to upload merge commits. It’s an add-on to the Push access right, and so it won’t be sufficient with only Push Merge Commit granted for a push to happen. Some projects wish to restrict merges to being created by Gerrit. By granting Push without Push Merge Commit, the only merges that enter the system will be those created by Gerrit.

The reference name connected to a Push Merge Commit entry must always be prefixed with refs/for/, for example refs/for/refs/heads/BRANCH. This applies even for an entry that complements a Push entry for refs/heads/BRANCH that allows direct pushes of non-merge commits, and the intention of the Push Merge Commit entry is to allow direct pushes of merge commits.

Create Annotated Tag

This category permits users to push an annotated tag object into the project’s repository. Typically this would be done with a command line such as:

  git push ssh://USER@HOST:PORT/PROJECT tag v1.0

Or:

  git push https://HOST/PROJECT tag v1.0

Tags must be annotated (created with git tag -a), should exist in the refs/tags/ namespace, and should be new.

This category is intended to be used to publish tags when a project reaches a stable release point worth remembering in history.

It allows for a new annotated (unsigned) tag to be created. The tagger email address must be verified for the current user.

To push tags created by users other than the current user (such as tags mirrored from an upstream project), Forge Committer Identity must be also granted in addition to Create Annotated Tag.

To push lightweight (non annotated) tags, grant Create Reference for reference name +refs/tags/*+, as lightweight tags are implemented just like branches in Git.

To delete or overwrite an existing tag, grant Push with the force option enabled for reference name +refs/tags/*+, as deleting a tag requires the same permission as deleting a branch.

To push an annotated tag on a new commit (commit not reachable from any branch/tag) grant Push permission on +refs/tags/*+ too. The Push permission on +refs/tags/*+ does not allow updating of annotated tags, not even fast-forwarding of annotated tags. Update of annotated tags is only allowed by granting Push with force option on +refs/tags/*+.

Create Signed Tag

This category permits users to push a PGP signed tag object into the project’s repository. Typically this would be done with a command line such as:

  git push ssh://USER@HOST:PORT/PROJECT tag v1.0

Or:

  git push https://HOST/PROJECT tag v1.0

Tags must be signed (created with git tag -s), should exist in the refs/tags/ namespace, and should be new.

Read

The Read category controls visibility to the project’s changes, comments, code diffs, and Git access over SSH or HTTP. A user must have this access granted in order to see a project, its changes, or any of its data.

This category has a special behavior, where the per-project ACL is evaluated before the global all projects ACL. If the per-project ACL has granted Read with DENY, and does not otherwise grant Read with ALLOW, then a Read in the all projects ACL is ignored. This behavior is useful to hide a handful of projects on an otherwise public server.

For an open source, public Gerrit installation it is common to grant Read to Anonymous Users in the All-Projects ACL, enabling casual browsing of any project’s changes, as well as fetching any project’s repository over SSH or HTTP. New projects can be temporarily hidden from public view by granting Read with DENY to Anonymous Users and granting Read to the project owner’s group within the per-project ACL.

For a private Gerrit installation using a trusted HTTP authentication source, granting Read to Registered Users may be more typical, enabling read access only to those users who have been able to authenticate through the HTTP access controls. This may be suitable in a corporate deployment if the HTTP access control is already restricted to the correct set of users.

Rebase

This category permits users to rebase changes via the web UI by pushing the Rebase Change button.

The change owner and submitters can always rebase changes in the web UI (even without having the Rebase access right assigned).

Users without this access right who are able to upload new patch sets can still do the rebase locally and upload the rebased commit as a new patch set.

Remove Reviewer

This category permits users to remove other users from the list of reviewers on a change.

Change owners can always remove reviewers who have given a zero or positive score (even without having the Remove Reviewer access right assigned).

Project owners and site administrators can always remove any reviewer (even without having the Remove Reviewer access right assigned).

Users without this access right can only remove themselves from the reviewer list on a change.

Review Labels

For every configured label My-Name in the project, there is a corresponding permission label-My-Name with a range corresponding to the defined values. There is also a corresponding labelAs-My-Name permission that enables editing another user’s label.

Gerrit comes pre-configured with a default Code-Review label that can be granted to groups within projects, enabling functionality for that group’s members. Custom labels may also be defined globally or on a per-project basis.

Submit

This category permits users to submit changes.

Submitting a change causes it to be merged into the destination branch as soon as possible, making it a permanent part of the project’s history.

In order to submit, all labels (such as Verified and Code-Review, above) must enable submit, and also must not block it. See above for details on each label.

To immediately submit a change on push the caller needs to have the Submit permission on refs/for/<ref> (e.g. on refs/for/refs/heads/master).

Submitting to the refs/meta/config branch is only allowed to project owners. Any explicit submit permissions for non-project-owners on this branch are ignored. By submitting to the refs/meta/config branch the configuration of the project is changed, which can include changes to the access rights of the project. Allowing this to be done by a non-project-owner would open a security hole enabling editing of access rights, and thus granting of powers beyond submitting to the configuration.

Submit (On Behalf Of)

This category permits users who have also been granted the Submit permission to submit changes on behalf of another user, by using the on_behalf_of field in SubmitInput when submitting using the REST API.

Note that this permission is named submitAs in the project.config file.

View Private Changes

This category permits users to view all private changes.

The change owner and any explicitly added reviewers can always see private changes (even without having the View Private Changes access right assigned).

Delete Own Changes

This category permits users to delete their own changes if they are not merged yet. This means only own changes that are open or abandoned can be deleted.

Edit Topic Name

This category permits users to edit the topic name of a change that is uploaded for review.

The change owner, branch owners, project owners, and site administrators can always edit the topic name (even without having the Edit Topic Name access right assigned).

Whether the topic can be edited on closed changes can be controlled by the Force Edit flag. If this flag is not set the topic can only be edited on open changes.

Edit Hashtags

This category permits users to add or remove hashtags on a change that is uploaded for review.

The change owner, branch owners, project owners, and site administrators can always edit or remove hashtags (even without having the Edit Hashtags access right assigned).

Edit Assignee

This category permits users to set who is assigned to a change that is uploaded for review.

The change owner, ref owners, and the user currently assigned to a change can always change the assignee.

Examples of typical roles in a project

Below follows a set of typical roles on a server and which access rights these roles typically should be granted. You may see them as general guidelines for a typical way to set up your project on a brand new Gerrit instance.

Contributor

This is the typical user on a public server. They are able to read your project and upload new changes to it. They are able to give feedback on other changes as well, but are unable to block or approve any changes.

Suggested access rights to grant:

• Read section_title on refs/heads/* and refs/tags/*

• Push section_title to refs/for/refs/heads/*

• Code-Review with range -1 to +1 for refs/heads/*

If it’s desired to have the possibility to upload temporarily hidden changes there’s a specific permission for that. This enables someone to add specific reviewers for early feedback before making the change publicly visible.

Developer

This is the typical core developer on a public server. They are able to read the project, upload changes to a branch. They are allowed to push merge commits to merge branches together. Also, they are allowed to forge author identity, thus handling commits belonging to others than themselves, effectively allowing them to transfer commits between different branches.

They are furthermore able to code review and verify commits, and eventually submit them. If you have an automated CI system that builds all uploaded patch sets you might want to skip the verification rights for the developer and let the CI system do that exclusively.

Suggested access rights to grant:

• Read section_title on refs/heads/* and refs/tags/*

• Push section_title to refs/for/refs/heads/*

• Push merge commit section_title to refs/for/refs/heads/*

• Forge Author Identity section_title to refs/heads/*

• Label: Code-Review with range -2 to +2 for refs/heads/*

• Label: Verified with range -1 to +1 for refs/heads/*

• Submit section_title on refs/heads/*

If the project is small or the developers are seasoned it might make sense to give them the freedom to push commits directly to a branch.

Optional access rights to grant:

• Push to refs/heads/*

• Push merge commit to refs/heads/*

CI system

A typical Continuous Integration system should be able to download new changes to build and then leave a verdict somehow.

As an example, the popular gerrit-trigger plugin for Jenkins/Hudson can set labels at:

• The start of a build

• A successful build

• An unstable build (tests fails)

• A failed build

Usually the range chosen for this verdict is the Verified label. Depending on the size of your project and discipline of involved developers you might want to limit access right to the +1 Verified label to the CI system only. That way it’s guaranteed that submitted commits always get built and pass tests successfully.

If the build doesn’t complete successfully the CI system can set the Verified label to -1. However that means that a failed build will block submit of the change even if someone else sets Verified +1. Depending on the project and how much the CI system can be trusted for accurate results, a blocking label might not be feasible. A recommended alternative is to set the label Code-review to -1 instead, as it isn’t a blocking label but still shows a red label in the Gerrit UI. Optionally, to enable the possibility to deliver different results (build error vs unstable for instance), it’s also possible to set Code-review +1 as well.

If pushing new changes is granted, it’s possible to automate cherry-pick of submitted changes for upload to other branches under certain conditions. This is probably not the first step of what a project wants to automate however, and so the push right can be found under the optional section.

Suggested access rights to grant, that won’t block changes:

• Read section_title on refs/heads/* and refs/tags/*

• Label: Code-Review with range -1 to 0 for refs/heads/*

• Label: Verified with range 0 to +1 for refs/heads/*

Optional access rights to grant:

• Label: Code-Review with range -1 to +1 for refs/heads/*

• Push section_title to refs/for/refs/heads/*

Integrator

Integrators are like developers but with some additional rights granted due to their administrative role in a project. They can upload or push any commit with any committer email (not just their own) and they can also create new tags and branches.

Suggested access rights to grant:

• Developer rights

• Push to refs/heads/*

• Push merge commit to refs/heads/*

• Forge Committer Identity to refs/for/refs/heads/*

• Create Reference to refs/heads/*

• Create Annotated Tag to refs/tags/*

Project owner

The project owner is almost like an integrator but with additional destructive power in the form of being able to delete branches. Optionally these users also have the power to configure access rights in gits assigned to them.

Warning

These users should be really knowledgeable about git, for instance knowing why tags never should be removed from a server. This role is granted potentially destructive access rights and cleaning up after such a mishap could be time consuming!

Suggested access rights to grant:

• Integrator rights

• Push with the force option to refs/heads/* and refs/tags/*

Optional access right to grant:

• Owner in the gits they mostly work with.

Administrator

The administrator role is the most powerful role known in the Gerrit universe. This role may grant itself (or others) any access right. By default the Administrators group is the group that has this role.

Mandatory access rights:

• The Administrate Server capability

Suggested access rights to grant:

• Project owner rights

• Any capabilities needed by the administrator

Enforcing site wide access policies

By granting the Owner access right on the +refs/*+ to a group, Gerrit administrators can delegate the responsibility of maintaining access rights for that project to that group.

In a corporate deployment it is often necessary to enforce some access policies. An example could be that no-one can update or delete a tag, not even the project owners. The ALLOW and DENY rules are not enough for this purpose as project owners can grant themselves any access right they wish and, thus, effectively override any inherited access rights from the “All-Projects” or some other common parent project.

What is needed is a mechanism to block a permission in a parent project so that even project owners cannot allow a blocked permission in their child project. Still, project owners should retain the possibility to manage all non-blocked rules as they wish. This gives best of both worlds:

• Gerrit administrators can concentrate on enforcing site wide policies and providing a meaningful set of default access permissions

• Project owners can manage access rights of their projects without a danger of violating a site wide policy

BLOCK access rule

The BLOCK rule blocks a permission globally. An inherited BLOCK rule cannot be overridden in the inheriting project. Any ALLOW rule from an inheriting project, which conflicts with an inherited BLOCK rule will not be honored. Searching for BLOCK rules, in the chain of parent projects, ignores the Exclusive flag, unless the rule with the Exclusive flag is defined on the same project as the BLOCK rule. This means within the same project a BLOCK rule can be overruled by ALLOW rules on the same access section and ALLOW rules with Exclusive flag on access section for more specific refs.

A BLOCK rule that blocks the push permission blocks any type of push, force or not. A blocking force push rule blocks only force pushes, but allows non-forced pushes if an ALLOW rule would have permitted it.

It is also possible to block label ranges. To block a group X from voting -2 and +2, but keep their existing voting permissions for the -1..+1 range intact we would define:

  [access "refs/heads/*"]
    label-Code-Review = block -2..+2 group X

The interpretation of the min..max range in case of a blocking rule is: block every vote from -INFINITE..min and max..INFINITE. For the example above it means that the range -1..+1 is not affected by this block.

BLOCK and ALLOW rules in the same access section

When an access section of a project contains a BLOCK and an ALLOW rule for the same permission then this ALLOW rule overrides the BLOCK rule:

  [access "refs/heads/*"]
    push = block group X
    push = group Y

In this case a user which is a member of the group Y will still be allowed to push to refs/heads/* even if it is a member of the group X.

Note

An ALLOW rule overrides a BLOCK rule only when both of them are inside the same access section of the same project. An ALLOW rule in a different access section of the same project or in any access section in an inheriting project cannot override a BLOCK rule.

Examples

The following examples show some possible use cases for the BLOCK rules.

Make sure no one can update or delete a tag

This requirement is quite common in a corporate deployment where reproducibility of a build must be guaranteed. To achieve that we block push permission for the Anonymous Users in “All-Projects”:

  [access "refs/tags/*"]
    push = block group Anonymous Users

By blocking the Anonymous Users we effectively block everyone as everyone is a member of that group. Note that the permission to create a tag is still necessary. Assuming that only project owners are allowed to create tags, we would extend the example above:

  [access "refs/tags/*"]
    push = block group Anonymous Users
    create = group Project Owners
    pushTag = group Project Owners

Let only a dedicated group vote in a special category

Assume there is a more restrictive process for submitting changes in stable release branches which is manifested as a new voting category Release-Process. Assume we want to make sure that only a Release Engineers group can vote in this category and that even project owners cannot approve this category. We have to block everyone except the Release Engineers to vote in this category and, of course, allow Release Engineers to vote in that category. In the “All-Projects” we define the following rules:

  [access "refs/heads/stable*"]
    label-Release-Process = block -1..+1 group Anonymous Users
    label-Release-Process = -1..+1 group Release Engineers

Global Capabilities

The global capabilities control actions that the administrators of the server can perform which usually affect the entire server in some way. The administrators may delegate these capabilities to trusted groups of users.

Delegation of capabilities allows groups to be granted a subset of administrative capabilities without being given complete administrative control of the server. This makes it possible to keep fewer users in the administrators group, even while spreading much of the server administration burden out to more users.

Global capabilities are assigned to groups in the access rights settings of the root project (“All-Projects”).

Below you find a list of capabilities available:

Access Database

Allow users to access the database using the gsql command, and view code review metadata refs in repositories.

Administrate Server

This is in effect the owner and administrator role of the Gerrit instance. Any members of a group granted this capability will be able to grant any access right to any group. They will also have all capabilities granted to them automatically.

In most installations only those users who have direct filesystem and database access should be granted this capability.

This capability does not imply any other access rights. Users that have this capability do not automatically get code review approval or submit rights in projects. This is a feature designed to permit administrative users to otherwise access Gerrit as any other normal user would, without needing two different accounts.

Batch Changes Limit

Allow site administrators to configure the batch changes limit for users to override the system config receive.maxBatchChanges.

Administrators can add a global block to All-Projects with group(s) that should have different limits.

When applying a batch changes limit to a user the largest value granted by any of their groups is used. 0 means no limit.

Create Account

Allow account creation over the ssh prompt. This capability allows the granted group members to create non-interactive service accounts. These service accounts are generally used for automation and made to be members of the Non-Interactive users group.

Create Group

Allow group creation. Groups are used to grant users access to different actions in projects. This capability allows the granted group members to either create new groups via ssh or via the web UI.

Create Project

Allow project creation. This capability allows the granted group to either create new git projects via ssh or via the web UI.

Email Reviewers

Allow or deny sending email to change reviewers and watchers. This can be used to deny build bots from emailing reviewers and people who watch the change. Instead, only the authors of the change and those who starred it will be emailed. The allow rules are evaluated before deny rules, however the default is to allow emailing, if no explicit rule is matched.

Flush Caches

Allow the flushing of Gerrit’s caches. This capability allows the granted group to flush some or all Gerrit caches via ssh.

Note

This capability doesn’t imply permissions to the show-caches command. For that you need the view caches capability.

Kill Task

Allow the operation of the kill command over ssh. The kill command ends tasks that currently occupy the Gerrit server, usually a replication task or a user initiated task such as an upload-pack or receive-pack.

Maintain Server

Allow basic, constrained server maintenance tasks, such as flushing caches and reindexing changes. Does not grant arbitrary database access, read/write, or ACL management permissions, as might the administrate server capability.

Implies the following capabilities:

• Flush Caches

• Kill Task

• Run Garbage Collection

• View Caches

• View Queue

Modify Account

Allow to modify accounts over the ssh prompt. This capability allows the granted group members to modify any user account setting.

Priority

This capability allows users to use the thread pool reserved for Non-Interactive Users. It’s a binary value in that granted users either have access to the thread pool, or they don’t.

There are three modes for this capability and they’re listed by rising priority:

• No capability configured.
  The user isn’t a member of a group with any priority capability granted. By default the user is then in the INTERACTIVE thread pool.

• BATCH
  If there’s a thread pool configured for Non-Interactive Users and a user is granted the priority capability with the BATCH mode selected, the user ends up in the separate batch user thread pool. This is true unless the user is also granted the below INTERACTIVE option.

• INTERACTIVE
  If a user is granted the priority capability with the INTERACTIVE option, regardless if they also have the BATCH option or not, they are in the INTERACTIVE thread pool.

Query Limit

Allow site administrators to configure the query limit for users to be above the default hard-coded value of 500. Administrators can add a global block to All-Projects with group(s) that should have different limits.

When applying a query limit to a user the largest value granted by any of their groups is used.

This limit applies not only to the gerrit query command, but also to the web UI results pagination size.

Run As

Allow users to impersonate any other user with the X-Gerrit-RunAs HTTP header on REST API calls, or the suexec SSH command.

When impersonating an administrator the Administrate Server capability is not honored. This security feature tries to prevent a role with Run As capability from modifying the access controls in All-Projects, however modification may still be possible if the impersonated user has permission to push or submit changes on refs/meta/config. Run As also blocks using most capabilities including Create User, Run Garbage Collection, etc., unless the capability is also explicitly granted to a group the administrator is a member of.

Administrators do not automatically inherit this capability; it must be explicitly granted.

Run Garbage Collection

Allow users to run the Git garbage collection for the repositories of all projects.

Stream Events

Allow performing streaming of Gerrit events. This capability allows the granted group to stream Gerrit events via ssh.

View All Accounts

Allow viewing all accounts for purposes of auto-completion, regardless of accounts.visibility setting.

View Caches

Allow querying for status of Gerrit’s internal caches. This capability allows the granted group to look at some or all Gerrit caches via ssh.

View Connections

Allow querying for status of Gerrit’s current client connections. This capability allows the granted group to look at Gerrit’s current connections via ssh.

View Plugins

Allow viewing the list of installed plugins.

View Queue

Allow querying for status of Gerrit’s internal task queue. This capability allows the granted group to look at the Gerrit task queue via ssh.

GERRIT

Part of Gerrit Code Review

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