fix fleetctl to set different CmdUID for Windows (#14895)

for #14891

cmd/fleetctl/mdm_test.go

@@ -205,7 +205,11 @@ func TestMDMRunCommand(t *testing.T) {
 				}
 				return hosts, nil
 			}
+			winCmds := map[string]struct{}{}
 			ds.MDMWindowsInsertCommandForHostsFunc = func(ctx context.Context, deviceIDs []string, cmd *fleet.MDMWindowsCommand) error {
+				// every command uuid is different
+				require.NotContains(t, winCmds, cmd.CommandUUID)
+				winCmds[cmd.CommandUUID] = struct{}{}
 				return nil
 			}
 			ds.GetMDMWindowsBitLockerStatusFunc = func(ctx context.Context, host *fleet.Host) (*fleet.HostMDMDiskEncryption, error) {

server/service/client_mdm.go

@@ -18,6 +18,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/beevik/etree"
 	"github.com/fleetdm/fleet/v4/pkg/file"
 	"github.com/fleetdm/fleet/v4/server/fleet"
 	"github.com/google/uuid"
@@ -334,7 +335,23 @@ func (c *Client) prepareWindowsMDMCommand(rawCmd []byte) ([]byte, error) {
 	if _, err := fleet.ParseWindowsMDMCommand(rawCmd); err != nil {
 		return nil, err
 	}
-	return rawCmd, nil
+
+	// ensure there's a CmdID with a random UUID value, we're manipulating
+	// the document this way to make sure we don't introduce any unintended
+	// changes to the command XML.
+	doc := etree.NewDocument()
+	if err := doc.ReadFromBytes(rawCmd); err != nil {
+		return nil, err
+	}
+	element := doc.FindElement("//CmdID")
+	// if we can't find a CmdID, just add one.
+	if element == nil {
+		root := doc.Root()
+		element = root.CreateElement("CmdID")
+	}
+	element.SetText(uuid.NewString())
+
+	return doc.WriteToBytes()
 }
 
 func (c *Client) prepareAppleMDMCommand(rawCmd []byte) ([]byte, error) {

server/service/client_mdm_test.go

@@ -0,0 +1,66 @@
+package service
+
+import (
+	"testing"
+
+	"github.com/beevik/etree"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestPrepareWindowsMDMCommand(t *testing.T) {
+	c := &Client{}
+
+	validXML := []byte(`
+	<Exec>
+		<CmdID>some-id</CmdID>
+		<Item></Item>
+	</Exec>
+	`)
+
+	invalidCmdXML := []byte(`
+	<Add>
+		<CmdID>some-id</Cmd>
+		<Item></Item>
+	</Add>
+	`)
+
+	noCmdIDXML := []byte(`
+	<Exec>
+		<Item></Item>
+	</Exec>
+	`)
+
+	t.Run("Modifies valid CmdID", func(t *testing.T) {
+		modified, err := c.prepareWindowsMDMCommand(validXML)
+		assert.Nil(t, err)
+
+		doc := etree.NewDocument()
+		err = doc.ReadFromBytes(modified)
+		assert.Nil(t, err)
+
+		element := doc.FindElement("//CmdID")
+		assert.NotNil(t, element)
+		assert.NotEmpty(t, element.Text())
+	})
+
+	t.Run("Adds CmdID if missing", func(t *testing.T) {
+		modified, err := c.prepareWindowsMDMCommand(noCmdIDXML)
+		assert.Nil(t, err)
+
+		doc := etree.NewDocument()
+		err = doc.ReadFromBytes(modified)
+		assert.Nil(t, err)
+
+		element := doc.FindElement("//CmdID")
+		assert.NotNil(t, element)
+		assert.NotEmpty(t, element.Text())
+	})
+
+	t.Run("Returns error on invalid XML", func(t *testing.T) {
+		_, err := c.prepareWindowsMDMCommand(invalidCmdXML)
+		assert.NotNil(t, err)
+
+		_, err = c.prepareWindowsMDMCommand([]byte("<Exec><Exec"))
+		assert.NotNil(t, err)
+	})
+}