Commit 88d83e2e authored by Kamil Trzciński's avatar Kamil Trzciński 🔴

Describe how the recent changes of CI permissions affect builds

parent 2450625b
......@@ -16,5 +16,7 @@
- [Trigger builds through the API](triggers/README.md)
- [Build artifacts](../user/project/builds/artifacts.md)
- [User permissions](../user/permissions.md#gitlab-ci)
- [Build permissions](../user/permissions.md#builds-permissions)
- [Access dependent projects](dependent_projects/README.md)
- [API](../api/ci/README.md)
- [CI services (linked docker containers)](services/README.md)
## Dependent projects
> Introduced in GitLab 8.12.
GitLab 8.12 introduces a new [Build permissions model](../../user/permissions.md#builds-permissions).
This opens an easy to use a way to access all dependent source codes:
1. Access project's `submodule`,
1. Access private Container Images,
1. Access project's and submodule LFS objects.
### Submodules
> It often happens that while working on one project, you need to use another project from within it.
> Perhaps it’s a library that a third party developed or that you’re developing separately and using in multiple parent projects.
> A common issue arises in these scenarios: you want to be able to treat the two projects as separate yet still be able to use one from within the other.
> (from https://git-scm.com/book/en/v2/Git-Tools-Submodules)
Your project usually have a file named `.gitmodules`.
This file usually looks like that:
```
[submodule "tools"]
path = tools
url = git@gitlab.com/group/tools.git
```
Before 8.12 you had to do a multiple workarounds (ex. [SSH keys](../ssh_keys/README.md))
in order to access the sources of `gitlab.com/group/tools`.
GitLab 8.12 uses your permissions to evaluate what a CI build can access.
More information about how this system works can be found here: [Build permissions model](../../user/permissions.md#builds-permissions).
To make use of a new changes you have to update your `.gitmodules` file to use a relative URL.
Let's consider the following example:
1. Your project is located at https://gitlab.com/secret-group/my-project,
1. To checkout your sources you usually use a SSH address: `git@gitlab.com:secret-group/my-project.git`,
1. Your project depend on https://gitlab.com/group/tools,
1. You have the `.gitmodules` file with above content.
Since that you can use a relative URLs for your `.gitmodules` configuration
it easily allows you to use an HTTP cloning for all your CI builds,
and SSH clonning for all your local checkouts.
If you change the `url` of your `tools` dependency:
```
git@gitlab.com/group/tools.git => ../../group/tools.git
```
It will instruct GIT to automatically deduce a URL that should be used when cloning sources.
Whether you used a HTTP or SSH it will instruct GIT to use the same channel.
And this will allow to make all your CI builds to use HTTPS (because GitLab CI uses HTTPS for cloning your sources),
and all your local clones will continue using SSH.
Given the above explanation, your `.gitmodules` file should look like this:
```
[submodule "tools"]
path = tools
url = ../../group/tools.git
```
However, you have to instruct GitLab CI to clone your submodules as this is not done automatically.
You can achieve that by adding a `before_script` section to your `.gitlab-ci.yml` with `git submodule` command:
```
before_script:
- git submodule update --init --recursive
test:
script:
- run-my-tests
```
This will make GitLab CI to initialize (fetch) and update (checkout) all your submodules recursively.
It can happen that your environment or your Docker Image does not have a git installed.
You have to either ask your Administrator or install the missing dependency yourself:
```
# Debian / Ubuntu
before_script:
- apt-get update -y
- apt-get install -y git-core
- git submodule update --init --recursive
# CentOS / RedHat
before_script:
- yum install git
- git submodule update --init --recursive
# Alpine
before_script:
- apk add -U git
- git submodule update --init --recursive
```
### Container Registry
With the update permission model we also extended support for accessing Container Registries for private projects.
> Note: As of 1.6 the GitLab Runner doesn't yet incorporate the introduced changes for permissions.
> This makes a `image:` to not work with private projects automatically.
> The manual configuration by Administrator is required to use private images.
> We plan to remove that limitation in one of the upcoming releases.
Your builds can access all container images that you would normally have access to.
The only implication is that you can push to Container Registry of project for which the build is triggered.
This is how the example usage can look like:
```
test:
script:
- docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN $CI_REGISTRY
- docker pull $CI_REGISTRY/group/other-project:latest
- docker run $CI_REGISTRY/group/other-project:latest
```
......@@ -138,3 +138,128 @@ instance and project. In addition, all admins can use the admin interface under
| Add shared runners | | | | ✓ |
| See events in the system | | | | ✓ |
| Admin interface | | | | ✓ |
## Builds permissions
> Changed in GitLab 8.12.
GitLab 8.12 has completely redesigned build permission system.
You can find all discussion and all our concerns when choosing the current approach:
https://gitlab.com/gitlab-org/gitlab-ce/issues/18994
We decided that builds permission should be tightly integrated with a permission
of a user who is triggering a build.
The reason to do it like that:
- We already have permission system in place: group and project membership of users,
- We already fully know who is triggering a build (using git push, using web, executing triggers),
- We already know what user is allowed to do,
- We use the user permission for builds that are triggered by him,
- This opens us a lot of possibilities to further enforce user permissions, like:
allowing only specific users to access runners, secure variables and environments,
- It is simple and convenient, that your build can access to everything that you have access to,
- We choose to short living unique tokens, granting access for time of the build,
Currently, any build that is triggered by the user, it's also signed with his permissions.
When user do `git push` or changes files through web (**the pusher**),
we will usually create a new Pipeline.
The Pipeline will be signed as created be the pusher.
Any build created in this pipeline will have the permissions of **the pusher**.
This allows us to make it really easy to evaluate access for all dependent projects,
container images that the pusher would have access too.
The permission is granted only for time that build is running.
The access is revoked after the build is finished.
It is important to note that we have a few types of Users:
- Administrators: CI builds created by Administrators would not have access to all GitLab projects,
but only to projects and container images of projects that the user is a member of or that are either public, or internal,
- External users: CI builds created by external users will have access only to projects to which user has at least reporter access,
this rules out accessing all internal projects by default,
This allows us to make the CI and permission system more trustable.
Let's consider the following scenario:
1. You are an employee of the company. Your company have number of internal tool repositories.
You have multiple CI builds that make use of this repositories.
2. You invite a new user, a visitor, the external user. CI builds created by that user do not have access to internal repositories,
because user also doesn't have the access from within GitLab. You as an employee have to grant explicit access for this user.
This allows us to prevent from accidental data leakage.
### Build privileges
This table shows granted privileges for builds triggered by specific types of users:
| Action | Guest, Reporter | Developer | Master | Admin |
|---------------------------------------------|-----------------|-------------|----------|--------|
| Run CI build | | ✓ | ✓ | ✓ |
| Clone source and LFS from current project | | ✓ | ✓ | ✓ |
| Clone source and LFS from other projects | | ✓ [^1] | ✓ [^1] | ✓ [^1] |
| Push source and LFS to current project | | | | |
| Push source and LFS to other projects | | | | |
| Pull container images from current project | | ✓ | ✓ | ✓ |
| Pull container images from other projects | | ✓ [^1] | ✓ [^1] | ✓ [^1] |
| Push container images to current project | | ✓ | ✓ | ✓ |
| Push container images to other projects | | | | |
### Build token
The above gives a question about trustability of build token.
Unique build token is generated for each project.
This build token allows to access all projects that would be normally accessible
to the user creating that build.
We try to make sure that this token doesn't leak.
We do that by:
1. Securing all API endpoints to not expose the build token,
1. Masking the build token from build logs,
1. Allowing to use the build token only when build is running,
However, this brings a question about runners security.
To make sure that this token doesn't leak you also make sure that you configure
your runners in most secure possible way, by avoiding using this configurations:
1. Any usage of `privileged` mode if the machines are re-used is risky,
1. Using `shell` executor,
By using in-secure GitLab Runner configuration you allow the rogue developers
to steal the tokens of other builds. However, this problem existed before,
but
### Before 8.12
In versions before 8.12 all CI builds would use runners token to checkout project sources.
The project runners token was a token that you would find in
[CI/CD Pipelines](https://gitlab.com/my-group/my-project/pipelines/settings).
The project runners token was used for registering new specific runners assigned to project
and to checkout project sources.
The project runners token could also be used to use GitLab Container Registry for that project,
allowing to pull and push Docker images from within CI build.
This token was limited to access only that project.
GitLab would create an special checkout URL:
```
https://gitlab-ci-token:<project-runners-token>/gitlab.com/gitlab-org/gitlab-ce.git
```
User could also use in his CI builds all docker related commands
to interact with GitLab Container Registry:
```
docker login -u gitlab-ci-token -p $CI_BUILD_TOKEN registry.gitlab.com
```
Using single token had multiple security implications:
- Token would be readable to anyone who has developer access to project who could run CI builds,
allowing to register any specific runner for a project,
- Token would allow to access only project sources,
forbidding to accessing any other projects,
- Token was not expiring, and multi-purpose: used for checking out sources,
for registering specific runners and for accessing project's container registry with read-write permissions
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