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94 lines
2.9 KiB
Go
94 lines
2.9 KiB
Go
/*
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Copyright 2020 The Kubernetes Authors.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package subjectrestriction
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import (
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"context"
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"fmt"
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"io"
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certificatesv1beta1 "k8s.io/api/certificates/v1beta1"
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"k8s.io/apiserver/pkg/admission"
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"k8s.io/klog/v2"
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certificatesapi "k8s.io/kubernetes/pkg/apis/certificates"
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)
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// PluginName is a string with the name of the plugin
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const PluginName = "CertificateSubjectRestriction"
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// Register registers the plugin
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func Register(plugins *admission.Plugins) {
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plugins.Register(PluginName, func(config io.Reader) (admission.Interface, error) {
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return NewPlugin(), nil
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})
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}
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// Plugin holds state for and implements the admission plugin.
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type Plugin struct {
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*admission.Handler
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}
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// ValidateInitialization always returns nil.
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func (p *Plugin) ValidateInitialization() error {
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return nil
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}
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var _ admission.ValidationInterface = &Plugin{}
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// NewPlugin constructs a new instance of the CertificateSubjectRestrictions admission interface.
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func NewPlugin() *Plugin {
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return &Plugin{
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Handler: admission.NewHandler(admission.Create),
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}
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}
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var csrGroupResource = certificatesapi.Resource("certificatesigningrequests")
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// Validate ensures that if the signerName on a CSR is set to
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// `kubernetes.io/kube-apiserver-client`, that its organization (group)
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// attribute is not set to `system:masters`.
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func (p *Plugin) Validate(_ context.Context, a admission.Attributes, _ admission.ObjectInterfaces) error {
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if a.GetResource().GroupResource() != csrGroupResource || a.GetSubresource() != "" {
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return nil
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}
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csr, ok := a.GetObject().(*certificatesapi.CertificateSigningRequest)
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if !ok {
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return admission.NewForbidden(a, fmt.Errorf("expected type CertificateSigningRequest, got: %T", a.GetObject()))
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}
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if csr.Spec.SignerName != certificatesv1beta1.KubeAPIServerClientSignerName {
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return nil
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}
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csrParsed, err := certificatesapi.ParseCSR(csr.Spec.Request)
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if err != nil {
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return admission.NewForbidden(a, fmt.Errorf("failed to parse CSR: %v", err))
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}
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for _, group := range csrParsed.Subject.Organization {
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if group == "system:masters" {
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klog.V(4).Infof("CSR %s rejected by admission plugin %s for attempting to use signer %s with system:masters group",
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csr.Name, PluginName, certificatesv1beta1.KubeAPIServerClientSignerName)
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return admission.NewForbidden(a, fmt.Errorf("use of %s signer with system:masters group is not allowed",
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certificatesv1beta1.KubeAPIServerClientSignerName))
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}
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}
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return nil
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}
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