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[TEP-0145] Add sanity check for CEL expression #7251

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Oct 23, 2023
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[TEP-0145] Add sanity check for CEL expression #7251

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13 changes: 12 additions & 1 deletion docs/pipelines.md
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Original file line number Diff line number Diff line change
Expand Up @@ -777,12 +777,23 @@ There are a lot of scenarios where `when` expressions can be really useful. Some

#### Use CEL expression in WhenExpression

> :seedling: **`CEL in WhenExpression` is an [alpha](install.md#alpha-features) feature.**
> :seedling: **`CEL in WhenExpression` is an [alpha](additional-configs.md#alpha-features) feature.**
> The `enable-cel-in-whenexpression` feature flag must be set to `"true"` to enable the use of `CEL` in `WhenExpression`.
>
> :warning: This feature is in a preview mode.
> It is still in a very early stage of development and is not yet fully functional

`CEL` expression is validated at admission webhook and a validation error will be returned if the expression is invalid.

**Note:** To use Tekton's [variable substitution](variables.md), you need to wrap the reference with single quotes. This also means that if you pass another CEL expression via `params` or `results`, it won't be executed. Therefore CEL injection is disallowed.

For example:
```
This is valid: '$(params.foo)' == 'foo'
This is invalid: $(params.foo) == 'foo'
CEL's variable substitution is not supported yet and thus invalid: params.foo == 'foo'
```

#### Guarding a `Task` and its dependent `Tasks`

To guard a `Task` and its dependent Tasks:
Expand Down
15 changes: 13 additions & 2 deletions pkg/apis/pipeline/v1/when_validation.go
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Expand Up @@ -21,8 +21,7 @@ import (
"fmt"
"strings"

// TODO(#7244): Pull the cel-go library for now, the following PR will use the library.
_ "github.com/google/cel-go/cel"
"github.com/google/cel-go/cel"
"github.com/tektoncd/pipeline/pkg/apis/config"
"k8s.io/apimachinery/pkg/api/equality"
"k8s.io/apimachinery/pkg/selection"
Expand Down Expand Up @@ -54,6 +53,18 @@ func (we *WhenExpression) validateWhenExpressionFields(ctx context.Context) *api
if we.Input != "" || we.Operator != "" || len(we.Values) != 0 {
return apis.ErrGeneric(fmt.Sprintf("cel and input+operator+values cannot be set in one WhenExpression: %v", we))
}

// We need to compile the CEL expression and check if it is a valid expression
// note that at the validation webhook, Tekton's variables are not substituted,
// so they need to be wrapped with single quotes.
// e.g. This is a valid CEL expression: '$(params.foo)' == 'foo';
// But this is not a valid expression since CEL cannot recognize: $(params.foo) == 'foo';
// This is not valid since we don't pass params to CEL's environment: params.foo == 'foo';
env, _ := cel.NewEnv()
_, iss := env.Compile(we.CEL)
if iss.Err() != nil {
return apis.ErrGeneric("invalid cel expression: %s with err: %s", we.CEL, iss.Err().Error())
}
return nil
}

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39 changes: 38 additions & 1 deletion pkg/apis/pipeline/v1/when_validation_test.go
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Expand Up @@ -116,10 +116,35 @@ func TestCELinWhenExpressions_Valid(t *testing.T) {
name string
wes WhenExpressions
}{{
name: "valid cel",
name: "valid operator - Equal",
wes: []WhenExpression{{
CEL: " 'foo' == 'foo' ",
}},
}, {
name: "valid operator - NotEqual",
wes: []WhenExpression{{
CEL: " 'foo' != 'foo' ",
}},
}, {
name: "valid operator - In",
wes: []WhenExpression{{
CEL: "'foo' in ['foo', 'bar']",
}},
}, {
name: "valid operator - NotIn",
wes: []WhenExpression{{
CEL: "!('foo' in ['foo', 'bar'])",
}},
}, {
name: "valid regex expression",
wes: []WhenExpression{{
CEL: "'release/v1'.matches('release/.*')",
}},
}, {
name: "valid variable reference syntax",
wes: []WhenExpression{{
CEL: "'$(params.foo)' in ['foo', 'bar']",
}},
}}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
Expand All @@ -141,6 +166,18 @@ func TestCELWhenExpressions_Invalid(t *testing.T) {
CEL: " 'foo' == 'foo' ",
}},
enableCELInWhenExpression: false,
}, {
name: "variable reference should be wrapped with single quotes",
wes: []WhenExpression{{
CEL: " $(params.foo) == 'foo' ",
}},
enableCELInWhenExpression: true,
}, {
name: "variables not declared in environment",
wes: []WhenExpression{{
CEL: " params.foo == 'foo' ",
}},
enableCELInWhenExpression: true,
}, {
name: "CEL should not coexist with input+operator+values",
wes: []WhenExpression{{
Expand Down
12 changes: 12 additions & 0 deletions pkg/apis/pipeline/v1beta1/when_validation.go
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ import (
"fmt"
"strings"

"github.com/google/cel-go/cel"
"github.com/tektoncd/pipeline/pkg/apis/config"
"k8s.io/apimachinery/pkg/api/equality"
"k8s.io/apimachinery/pkg/selection"
Expand Down Expand Up @@ -52,6 +53,17 @@ func (we *WhenExpression) validateWhenExpressionFields(ctx context.Context) *api
if we.Input != "" || we.Operator != "" || len(we.Values) != 0 {
return apis.ErrGeneric(fmt.Sprintf("cel and input+operator+values cannot be set in one WhenExpression: %v", we))
}
// We need to compile the CEL expression and check if it is a valid expression
// note that at the validation webhook, Tekton's variables are not substituted,
// so they need to be wrapped with single quotes.
// e.g. This is a valid CEL expression: '$(params.foo)' == 'foo';
// But this is not a valid expression since CEL cannot recognize: $(params.foo) == 'foo';
// This is not valid since we don't pass params to CEL's environment: params.foo == 'foo';
env, _ := cel.NewEnv()
_, iss := env.Compile(we.CEL)
if iss.Err() != nil {
return apis.ErrGeneric("invalid cel expression: %s with err: %s", we.CEL, iss.Err().Error())
}
return nil
}

Expand Down
39 changes: 38 additions & 1 deletion pkg/apis/pipeline/v1beta1/when_validation_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -116,10 +116,35 @@ func TestCELinWhenExpressions_Valid(t *testing.T) {
name string
wes WhenExpressions
}{{
name: "valid cel",
name: "valid operator - Equal",
wes: []WhenExpression{{
CEL: " 'foo' == 'foo' ",
}},
}, {
name: "valid operator - NotEqual",
wes: []WhenExpression{{
CEL: " 'foo' != 'foo' ",
}},
}, {
name: "valid operator - In",
wes: []WhenExpression{{
CEL: "'foo' in ['foo', 'bar']",
}},
}, {
name: "valid operator - NotIn",
wes: []WhenExpression{{
CEL: "!('foo' in ['foo', 'bar'])",
}},
}, {
name: "valid regex expression",
wes: []WhenExpression{{
CEL: "'release/v1'.matches('release/.*')",
}},
}, {
name: "valid variable reference syntax",
wes: []WhenExpression{{
CEL: "'$(params.foo)' in ['foo', 'bar']",
}},
}}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
Expand All @@ -141,6 +166,18 @@ func TestCELWhenExpressions_Invalid(t *testing.T) {
CEL: " 'foo' == 'foo' ",
}},
enableCELInWhenExpression: false,
}, {
name: "variable reference should be wrapped with single quotes",
wes: []WhenExpression{{
CEL: " $(params.foo) == 'foo' ",
}},
enableCELInWhenExpression: true,
}, {
name: "variables not declared in environment",
wes: []WhenExpression{{
CEL: " params.foo == 'foo' ",
}},
enableCELInWhenExpression: true,
}, {
name: "CEL should not coexist with input+operator+values",
wes: []WhenExpression{{
Expand Down
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