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[kube] fix greedy deny rule blocking namespace list when blocking oth…
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…er resources (#44893) (#44975)

* [kube] fix greedy deny rule blocking namespace list when blocking other resources

This PR fixes an edge case where the deny rule for blocking access to a resource becomes greedy and blocks access to the whole namespace.

eg:

```
  allow:
    kubernetes_labels:
      '*': '*'
    kubernetes_resources:
    - kind: '*'
      name: '*'
      namespace: '*'
      verbs:
      - '*'
  deny:
    kubernetes_resources:
    - kind: secret
      name: '*'
      namespace: '*'
      verbs:
      - '*'

```

With the example above, access to secrets must be blocked but the user is allowed to access every other resource in any namespace.
The previous model was greedy and blocked access to namespace list.

* add extra test

* handle comments
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@tigrato
tigrato authored Aug 1, 2024
1 parent 226ce68 commit e526768
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Showing 4 changed files with 121 additions and 7 deletions.
4 changes: 2 additions & 2 deletions lib/kube/proxy/forwarder.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1109,14 +1109,14 @@ func matchKubernetesResource(resource types.KubernetesResource, allowed, denied
// utils.KubeResourceMatchesRegex checks if the resource.Kind is strictly equal
// to each entry and validates if the Name and Namespace fields matches the
// regex allowed by each entry.
result, err := utils.KubeResourceMatchesRegex(resource, denied)
result, err := utils.KubeResourceMatchesRegex(resource, denied, types.Deny)
if err != nil {
return false, trace.Wrap(err)
} else if result {
return false, nil
}

result, err = utils.KubeResourceMatchesRegex(resource, allowed)
result, err = utils.KubeResourceMatchesRegex(resource, allowed, types.Allow)
if err != nil {
return false, trace.Wrap(err)
}
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2 changes: 1 addition & 1 deletion lib/services/role.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2398,7 +2398,7 @@ func NewKubernetesResourceMatcher(resource types.KubernetesResource) *Kubernetes

// Match matches a Kubernetes Resource against provided role and condition.
func (m *KubernetesResourceMatcher) Match(role types.Role, condition types.RoleConditionType) (bool, error) {
result, err := utils.KubeResourceMatchesRegex(m.resource, role.GetKubeResources(condition))
result, err := utils.KubeResourceMatchesRegex(m.resource, role.GetKubeResources(condition), condition)

return result, trace.Wrap(err)
}
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6 changes: 3 additions & 3 deletions lib/utils/replace.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -149,14 +149,14 @@ const (
// input is the resource we are checking for access.
// resources is a list of resources that the user has access to - collected from
// their roles that match the Kubernetes cluster where the resource is defined.
func KubeResourceMatchesRegex(input types.KubernetesResource, resources []types.KubernetesResource) (bool, error) {
// cond is the deny or allow condition of the role that we are evaluating.
func KubeResourceMatchesRegex(input types.KubernetesResource, resources []types.KubernetesResource, cond types.RoleConditionType) (bool, error) {
if len(input.Verbs) != 1 {
return false, trace.BadParameter("only one verb is supported, input: %v", input.Verbs)
}
// isClusterWideResource is true if the resource is cluster-wide, e.g. a
// namespace resource or a clusterrole.
isClusterWideResource := slices.Contains(types.KubernetesClusterWideResourceKinds, input.Kind)

verb := input.Verbs[0]
// If the user is list/read/watch a namespace, they should be able to see the
// namespace they have resources defined for.
Expand Down Expand Up @@ -191,7 +191,7 @@ func KubeResourceMatchesRegex(input types.KubernetesResource, resources []types.
if ok, err := MatchString(input.Namespace, resource.Name); err != nil || ok {
return ok, trace.Wrap(err)
}
case targetsReadOnlyNamespace && resource.Kind != types.KindKubeNamespace && resource.Namespace != "":
case targetsReadOnlyNamespace && cond == types.Allow && resource.Kind != types.KindKubeNamespace && resource.Namespace != "":
// If the user requests a read-only namespace get/list/watch, they should
// be able to see the list of namespaces they have resources defined in.
// This means that if the user has access to pods in the "foo" namespace,
Expand Down
116 changes: 115 additions & 1 deletion lib/utils/replace_test.go
View file
Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
name string
input types.KubernetesResource
resources []types.KubernetesResource
action types.RoleConditionType
matches bool
assert require.ErrorAssertionFunc
}{
Expand All @@ -180,8 +181,102 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.Error,
action: types.Allow,
matches: false,
},
{
name: "list namespace matches resource",
input: types.KubernetesResource{
Kind: types.KindNamespace,
Verbs: []string{types.KubeVerbList},
},
resources: []types.KubernetesResource{
{
Kind: types.KindKubeSecret,
Namespace: "*",
Name: "*",
Verbs: []string{types.Wildcard},
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
name: "list namespace doesn't match denying secrets",
input: types.KubernetesResource{
Kind: types.KindNamespace,
Verbs: []string{types.KubeVerbList},
},
resources: []types.KubernetesResource{
{
Kind: types.KindKubeSecret,
Namespace: "*",
Name: "*",
Verbs: []string{types.Wildcard},
},
},
assert: require.NoError,
action: types.Deny,
matches: false,
},
{
name: "get namespace match denying everything",
input: types.KubernetesResource{
Kind: types.KindNamespace,
Name: "default",
Verbs: []string{types.KubeVerbGet},
},
resources: []types.KubernetesResource{
{
Kind: types.Wildcard,
Namespace: types.Wildcard,
Name: types.Wildcard,
Verbs: []string{types.Wildcard},
},
},
assert: require.NoError,
action: types.Deny,
matches: true,
},
{
name: "get namespace doesn't match denying secrets",
input: types.KubernetesResource{
Kind: types.KindNamespace,
Name: "default",
Verbs: []string{types.KubeVerbGet},
},
resources: []types.KubernetesResource{
{
Kind: types.KindKubeSecret,
Namespace: "*",
Name: "*",
Verbs: []string{types.Wildcard},
},
},
assert: require.NoError,
action: types.Deny,
matches: false,
},
{
name: "get secret matches denying secrets",
input: types.KubernetesResource{
Kind: types.KindKubeSecret,
Name: "default",
Verbs: []string{types.KubeVerbGet},
},
resources: []types.KubernetesResource{
{
Kind: types.KindKubeSecret,
Namespace: "*",
Name: "*",
Verbs: []string{types.Wildcard},
},
},
assert: require.NoError,
action: types.Deny,
matches: true,
},
{
name: "input matches single resource with wildcard verb",
input: types.KubernetesResource{
Expand All @@ -199,6 +294,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -218,6 +314,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -237,6 +334,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
{
Expand All @@ -255,6 +353,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
{
Expand Down Expand Up @@ -286,6 +385,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -305,6 +405,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -324,6 +425,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
{
Expand All @@ -342,6 +444,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
Verbs: []string{types.Wildcard},
},
},
action: types.Allow,
assert: require.Error,
},
{
Expand All @@ -359,6 +462,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
Name: "podname",
},
},
action: types.Allow,
assert: require.NoError,
},
{
Expand All @@ -376,6 +480,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -394,6 +499,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -412,6 +518,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
{
Expand All @@ -430,6 +537,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},

Expand All @@ -449,6 +557,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},

Expand All @@ -468,6 +577,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -486,6 +596,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},

Expand All @@ -505,6 +616,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: true,
},
{
Expand All @@ -523,6 +635,7 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
{
Expand All @@ -547,12 +660,13 @@ func TestKubeResourceMatchesRegex(t *testing.T) {
},
},
assert: require.NoError,
action: types.Allow,
matches: false,
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
got, err := KubeResourceMatchesRegex(tt.input, tt.resources)
got, err := KubeResourceMatchesRegex(tt.input, tt.resources, tt.action)
tt.assert(t, err)
require.Equal(t, tt.matches, got)
})
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