3 files changed, 193 insertions, 0 deletions
diff --git a/runsc/specutils/safemount_test/BUILD b/runsc/specutils/safemount_test/BUILD
new file mode 100644
index 000000000..c39c40492
--- /dev/null
+++ b/runsc/specutils/safemount_test/BUILD
@@ -0,0 +1,23 @@
+load("//tools:defs.bzl", "go_binary", "go_test")
+
+package(licenses = ["notice"])
+
+go_test(
+    name = "safemount_test",
+    size = "small",
+    srcs = ["safemount_test.go"],
+    data = [":safemount_runner"],
+    deps = [
+        "//pkg/test/testutil",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
+
+go_binary(
+    name = "safemount_runner",
+    srcs = ["safemount_runner.go"],
+    deps = [
+        "//runsc/specutils",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
diff --git a/runsc/specutils/safemount_test/safemount_runner.go b/runsc/specutils/safemount_test/safemount_runner.go
new file mode 100644
index 000000000..b23193033
--- /dev/null
+++ b/runsc/specutils/safemount_test/safemount_runner.go
@@ -0,0 +1,117 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// safemount_runner is used to test the SafeMount function. Because use of
+// unix.Mount requires privilege, tests must launch this process with
+// CLONE_NEWNS and CLONE_NEWUSER.
+package main
+
+import (
+	"errors"
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/runsc/specutils"
+)
+
+func main() {
+	// The test temporary directory is the first argument.
+	tempdir := os.Args[1]
+
+	tcs := []struct {
+		name     string
+		testfunc func() error
+	}{{
+		name: "unix.Mount to folder succeeds",
+		testfunc: func() error {
+			dir2Path := filepath.Join(tempdir, "subdir2")
+			if err := unix.Mount(filepath.Join(tempdir, "subdir"), dir2Path, "bind", unix.MS_BIND, ""); err != nil {
+				return fmt.Errorf("mount: %v", err)
+			}
+			return unix.Unmount(dir2Path, unix.MNT_DETACH)
+		},
+	}, {
+		// unix.Mount doesn't care whether the target is a symlink.
+		name: "unix.Mount to symlink succeeds",
+		testfunc: func() error {
+			symlinkPath := filepath.Join(tempdir, "symlink")
+			if err := unix.Mount(filepath.Join(tempdir, "subdir"), symlinkPath, "bind", unix.MS_BIND, ""); err != nil {
+				return fmt.Errorf("mount: %v", err)
+			}
+			return unix.Unmount(symlinkPath, unix.MNT_DETACH)
+		},
+	}, {
+		name: "SafeMount to folder succeeds",
+		testfunc: func() error {
+			dir2Path := filepath.Join(tempdir, "subdir2")
+			if err := specutils.SafeMount(filepath.Join(tempdir, "subdir"), dir2Path, "bind", unix.MS_BIND, "", "/proc"); err != nil {
+				return fmt.Errorf("SafeMount: %v", err)
+			}
+			return unix.Unmount(dir2Path, unix.MNT_DETACH)
+		},
+	}, {
+		name: "SafeMount to symlink fails",
+		testfunc: func() error {
+			err := specutils.SafeMount(filepath.Join(tempdir, "subdir"), filepath.Join(tempdir, "symlink"), "bind", unix.MS_BIND, "", "/proc")
+			if err == nil {
+				return fmt.Errorf("SafeMount didn't fail, but should have")
+			}
+			var symErr *specutils.ErrSymlinkMount
+			if !errors.As(err, &symErr) {
+				return fmt.Errorf("expected SafeMount to fail with ErrSymlinkMount, but got: %v", err)
+			}
+			return nil
+		},
+	}}
+
+	for _, tc := range tcs {
+		if err := runTest(tempdir, tc.testfunc); err != nil {
+			log.Fatalf("failed test %q: %v", tc.name, err)
+		}
+	}
+}
+
+// runTest runs testfunc with the following directory structure:
+// tempdir/
+//   subdir/
+//   subdir2/
+//   symlink --> ./subdir2
+func runTest(tempdir string, testfunc func() error) error {
+	// Create tempdir/subdir/.
+	dirPath := filepath.Join(tempdir, "subdir")
+	if err := os.Mkdir(dirPath, 0777); err != nil {
+		return fmt.Errorf("os.Mkdir(%s, 0777)", dirPath)
+	}
+	defer os.Remove(dirPath)
+
+	// Create tempdir/subdir2/.
+	dir2Path := filepath.Join(tempdir, "subdir2")
+	if err := os.Mkdir(dir2Path, 0777); err != nil {
+		return fmt.Errorf("os.Mkdir(%s, 0777)", dir2Path)
+	}
+	defer os.Remove(dir2Path)
+
+	// Create tempdir/symlink, which points to ./subdir2.
+	symlinkPath := filepath.Join(tempdir, "symlink")
+	if err := os.Symlink("./subdir2", symlinkPath); err != nil {
+		return fmt.Errorf("failed to create symlink %s: %v", symlinkPath, err)
+	}
+	defer os.Remove(symlinkPath)
+
+	// Run the actual test.
+	return testfunc()
+}
diff --git a/runsc/specutils/safemount_test/safemount_test.go b/runsc/specutils/safemount_test/safemount_test.go
new file mode 100644
index 000000000..8820978c4
--- /dev/null
+++ b/runsc/specutils/safemount_test/safemount_test.go
@@ -0,0 +1,53 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package safemount_test
+
+import (
+	"os"
+	"os/exec"
+	"syscall"
+	"testing"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/test/testutil"
+)
+
+func TestSafeMount(t *testing.T) {
+	// We run the actual tests in another process, as we need CAP_SYS_ADMIN to
+	// call mount(2). The new process runs in its own user and mount namespaces.
+	runner, err := testutil.FindFile("runsc/specutils/safemount_test/safemount_runner")
+	if err != nil {
+		t.Fatalf("failed to find test runner binary: %v", err)
+	}
+	cmd := exec.Command(runner, t.TempDir())
+	cmd.SysProcAttr = &unix.SysProcAttr{
+		Cloneflags: unix.CLONE_NEWNS | unix.CLONE_NEWUSER,
+		UidMappings: []syscall.SysProcIDMap{
+			{ContainerID: 0, HostID: os.Getuid(), Size: 1},
+		},
+		GidMappings: []syscall.SysProcIDMap{
+			{ContainerID: 0, HostID: os.Getgid(), Size: 1},
+		},
+		GidMappingsEnableSetgroups: false,
+		Credential: &syscall.Credential{
+			Uid: 0,
+			Gid: 0,
+		},
+	}
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Fatalf("failed running %s with error: %v\ntest output:\n%s", cmd, err, output)
+	}
+}