oci: Improve testing of overlay cleanup

e2e/actions/actions.go

@@ -2584,14 +2584,15 @@ func E2ETests(env e2e.TestEnv) testhelper.Tests {
 		//
 		// OCI Runtime Mode
 		//
-		"ociRun":     c.actionOciRun,        // singularity run --oci
-		"ociExec":    c.actionOciExec,       // singularity exec --oci
-		"ociShell":   c.actionOciShell,      // singularity shell --oci
-		"ociNetwork": c.actionOciNetwork,    // singularity exec --oci --net
-		"ociBinds":   c.actionOciBinds,      // singularity exec --oci --bind / --mount
-		"ociCdi":     c.actionOciCdi,        // singularity exec --oci --cdi
-		"ociIDMaps":  c.actionOciIDMaps,     // check uid/gid mapping on host for --oci as user / --fakeroot
-		"ociCompat":  np(c.actionOciCompat), // --oci equivalence to native mode --compat
-		"ociOverlay": (c.actionOciOverlay),  // --overlay in OCI mode
+		"ociRun":             c.actionOciRun,                 // singularity run --oci
+		"ociExec":            c.actionOciExec,                // singularity exec --oci
+		"ociShell":           c.actionOciShell,               // singularity shell --oci
+		"ociNetwork":         c.actionOciNetwork,             // singularity exec --oci --net
+		"ociBinds":           c.actionOciBinds,               // singularity exec --oci --bind / --mount
+		"ociCdi":             c.actionOciCdi,                 // singularity exec --oci --cdi
+		"ociIDMaps":          c.actionOciIDMaps,              // check uid/gid mapping on host for --oci as user / --fakeroot
+		"ociCompat":          np(c.actionOciCompat),          // --oci equivalence to native mode --compat
+		"ociOverlay":         (c.actionOciOverlay),           // --overlay in OCI mode
+		"ociOverlayTeardown": np(c.actionOciOverlayTeardown), // proper overlay unmounting in OCI mode
 	}
 }

e2e/actions/oci.go

@@ -6,6 +6,7 @@
 package actions
 
 import (
+	"bufio"
 	"encoding/json"
 	"fmt"
 	"os"
@@ -19,6 +20,7 @@ import (
 	cdispecs "github.com/container-orchestrated-devices/container-device-interface/specs-go"
 	"github.com/sylabs/singularity/e2e/internal/e2e"
 	"github.com/sylabs/singularity/internal/pkg/util/fs"
+	"gotest.tools/v3/assert"
 )
 
 func (c actionTests) actionOciRun(t *testing.T) {
@@ -1074,3 +1076,56 @@ func (c actionTests) actionOciOverlay(t *testing.T) {
 		})
 	}
 }
+
+// actionOciOverlayTeardown checks that OCI-mode overlays are correctly
+// unmounted even in root mode (i.e., when user namespaces are not involved).
+func (c actionTests) actionOciOverlayTeardown(t *testing.T) {
+	e2e.EnsureOCIArchive(t, c.env)
+	imageRef := "oci-archive:" + c.env.OCIArchivePath
+
+	const mountInfoPath string = "/proc/self/mountinfo"
+	numMountLinesPre, err := countLines(mountInfoPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	tmpDir, cleanup := e2e.MakeTempDir(t, c.env.TestDir, "oci_overlay_teardown-", "")
+	t.Cleanup(func() {
+		if !t.Failed() {
+			cleanup(t)
+		}
+	})
+
+	c.env.RunSingularity(
+		t,
+		e2e.WithProfile(e2e.OCIRootProfile),
+		e2e.WithCommand("exec"),
+		e2e.WithArgs("--overlay", tmpDir+":ro", imageRef, "/bin/true"),
+		e2e.ExpectExit(0),
+	)
+
+	numMountLinesPost, err := countLines(mountInfoPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(
+		t, numMountLinesPost, numMountLinesPre,
+		"Number of mounts after running in OCI-mode with overlays (%d) does not match the number before the run (%d)", numMountLinesPost, numMountLinesPre)
+}
+
+func countLines(path string) (int, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return -1, err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	lines := 0
+	for scanner.Scan() {
+		lines++
+	}
+
+	return lines, nil
+}