Fixes#3260
## Summary
Currently, Linkerd uses a service Account token to validate a pod
during the `Certify` request with identity, through which identity
is established on the proxy. This works well and good, as Kubernetes
attaches the `default` service account token of a namespace as a volume
(unless overridden with a specific service account by the user). Catch
here being that this token is aimed at the application to talk to the
kubernetes API and not specifically for Linkerd. This means that there
are [controls outside of Linkerd](https://kubernetes.io/docs/tasks/configure-pod-container/configure-service-account/#use-the-default-service-account-to-access-the-api-server), to manage this service token, which
users might want to use, [causing problems with Linkerd](https://github.com/linkerd/linkerd2/issues/3183)
as Linkerd might expect it to be present.
To have a more granular control over the token, and not rely on the
service token that can be managed externally, [Bound Service Tokens](https://github.com/kubernetes/enhancements/tree/master/keps/sig-auth/1205-bound-service-account-tokens)
can be used to generate tokens that are specifically for Linkerd,
that are bound to a specific pod, along with an expiry.
## Background on Bounded Service Tokens
This feature has been GA’ed in Kubernetes 1.20, and is enabled by default
in most cloud provider distributions. Using this feature, Kubernetes can
be asked to issue specific tokens for linkerd usage (through audience bound
configuration), with a specific expiry time (as the validation happens every
24 hours when establishing identity, we can follow the same), bounded to
a specific pod (meaning verification fails if the pod object isn’t available).
Because of all these bounds, and not being able to use this token for
anything else, This feels like the right thing to rely on to validate
a pod to issue a certificate.
### Pod Identity Name
We still use the same service account name as the pod identity
(used with metrics, etc) as these tokens are all generated from the
same base service account attached to the pod (could be defualt, or
the user overriden one). This can be verified by looking at the `user`
field in the `TokenReview` response.
<details>
<summary>Sample TokenReview response</summary>
Here, The new token was created for the vault audience for a pod which
had a serviceAccount token volume projection and was using the `mine`
serviceAccount in the default namespace.
```json
"kind": "TokenReview",
"apiVersion": "authentication.k8s.io/v1",
"metadata": {
"creationTimestamp": null,
"managedFields": [
{
"manager": "curl",
"operation": "Update",
"apiVersion": "authentication.k8s.io/v1",
"time": "2021-10-19T19:21:40Z",
"fieldsType": "FieldsV1",
"fieldsV1": {"f:spec":{"f:audiences":{},"f:token":{}}}
}
]
},
"spec": {
"token": "....",
"audiences": [
"vault"
]
},
"status": {
"authenticated": true,
"user": {
"username": "system:serviceaccount:default:mine",
"uid": "889a81bd-e31c-4423-b542-98ddca89bfd9",
"groups": [
"system:serviceaccounts",
"system:serviceaccounts:default",
"system:authenticated"
],
"extra": {
"authentication.kubernetes.io/pod-name": [
"nginx"
],
"authentication.kubernetes.io/pod-uid": [
"ebf36f80-40ee-48ee-a75b-96dcc21466a6"
]
}
},
"audiences": [
"vault"
]
}
```
</details>
## Changes
- Update `proxy-injector` and install scripts to include the new
projected Volume and VolumeMount.
- Update the `identity` pod to validate the token with the linkerd
audience key.
- Added `identity.serviceAccountTokenProjection` to disable this
feature.
- Updated err'ing logic with `autoMountServiceAccount: false`
to fail only when this feature is disabled.
Signed-off-by: Tarun Pothulapati <tarunpothulapati@outlook.com>
Fixes#4191#4993
This bumps Kubernetes client-go to the latest v0.19.2 (We had to switch directly to 1.19 because of this issue). Bumping to v0.19.2 required upgrading to smi-sdk-go v0.4.1. This also depends on linkerd/stern#5
This consists of the following changes:
- Fix ./bin/update-codegen.sh by adding the template path to the gen commands, as it is needed after we moved to GOMOD.
- Bump all k8s related dependencies to v0.19.2
- Generate CRD types, client code using the latest k8s.io/code-generator
- Use context.Context as the first argument, in all code paths that touch the k8s client-go interface
Signed-off-by: Tarun Pothulapati <tarunpothulapati@outlook.com>
This change introduces a new Identity service implementation for the
`io.linkerd.proxy.identity.Identity` gRPC service.
The `pkg/identity` contains a core, abstract implementation of the service
(generic over both the CA and (Kubernetes) Validator interfaces).
`controller/identity` includes a concrete implementation that uses the
Kubernetes TokenReview API to validate serviceaccount tokens when
issuing certificates.
This change does **NOT** alter installation or runtime to include the
identity service. This will be included in a follow-up.
Tarun Pothulapati
Oliver Gould