exec function working dir is the kustomization that referenced it (#4125)

* exec function working dir is the kustomization that referenced it

* suggested changes

* more code review

* use a field instead of an annotation

* more code review

kyaml/fn/runtime/exec/exec.go

@@ -7,7 +7,9 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"path/filepath"
 
+	"sigs.k8s.io/kustomize/kyaml/errors"
 	"sigs.k8s.io/kustomize/kyaml/fn/runtime/runtimeutil"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
@@ -19,6 +21,10 @@ type Filter struct {
 	// Args are the arguments to the executable
 	Args []string `yaml:"args,omitempty"`
 
+	// WorkingDir is the working directory that the executable
+	// should run in
+	WorkingDir string
+
 	runtimeutil.FunctionFilter
 }
 
@@ -32,5 +38,16 @@ func (c *Filter) Run(reader io.Reader, writer io.Writer) error {
 	cmd.Stdin = reader
 	cmd.Stdout = writer
 	cmd.Stderr = os.Stderr
+	if c.WorkingDir != "" {
+		if !filepath.IsAbs(c.WorkingDir) {
+			return errors.Errorf(
+				"relative working directory %s not allowed", c.WorkingDir)
+		}
+		if c.WorkingDir == "/" {
+			return errors.Errorf(
+				"root working directory '/' not allowed")
+		}
+		cmd.Dir = c.WorkingDir
+	}
 	return cmd.Run()
 }