Fix linux mount calls not applying propagation type changes

Propagation type changes must be done as a separate call, in the
same way as read only bind mounts.

To fix this:
1. Ensure propagation type change flags aren't included in other calls.
2. Apply propagation type change in a separate call.

Also:
* Make it clear which parameters are ignored by passing them as empty.
* Add tests to ensure Mount options are applied correctly.

Fixes moby#30415

Signed-off-by: Steven Hartland <steven.hartland@multiplay.co.uk>

pkg/mount/mounter_linux.go

@@ -4,15 +4,50 @@ import (
 	"syscall"
 )
 
-func mount(device, target, mType string, flag uintptr, data string) error {
-	if err := syscall.Mount(device, target, mType, flag, data); err != nil {
-		return err
+const (
+	// ptypes is the set propagation types.
+	ptypes = syscall.MS_SHARED | syscall.MS_PRIVATE | syscall.MS_SLAVE | syscall.MS_UNBINDABLE
+
+	// pflags is the full set valid flags for a change propagation call.
+	pflags = ptypes | syscall.MS_REC | syscall.MS_SILENT
+
+	// broflags is the combination of bind and read only
+	broflags = syscall.MS_BIND | syscall.MS_RDONLY
+)
+
+// isremount returns true if either device name or flags identify a remount request, false otherwise.
+func isremount(device string, flags uintptr) bool {
+	switch {
+	// We treat device "" and "none" as a remount request to provide compatibility with
+	// requests that don't explicitly set MS_REMOUNT such as those manipulating bind mounts.
+	case flags&syscall.MS_REMOUNT != 0, device == "", device == "none":
+		return true
+	default:
+		return false
+	}
+}
+
+func mount(device, target, mType string, flags uintptr, data string) error {
+	oflags := flags &^ ptypes
+	if !isremount(device, flags) {
+		// Initial call applying all non-propagation flags.
+		if err := syscall.Mount(device, target, mType, oflags, data); err != nil {
+			return err
+		}
 	}
 
-	// If we have a bind mount or remount, remount...
-	if flag&syscall.MS_BIND == syscall.MS_BIND && flag&syscall.MS_RDONLY == syscall.MS_RDONLY {
-		return syscall.Mount(device, target, mType, flag|syscall.MS_REMOUNT, data)
+	if flags&ptypes != 0 {
+		// Change the propagation type.
+		if err := syscall.Mount("", target, "", flags&pflags, ""); err != nil {
+			return err
+		}
 	}
+
+	if oflags&broflags == broflags {
+		// Remount the bind to apply read only.
+		return syscall.Mount("", target, "", oflags|syscall.MS_REMOUNT, "")
+	}
+
 	return nil
 }
 

pkg/mount/mounter_linux_test.go

@@ -0,0 +1,195 @@
+// +build linux
+
+package mount
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestMount(t *testing.T) {
+	if os.Getuid() != 0 {
+		t.Skip("not root tests would fail")
+	}
+
+	source, err := ioutil.TempDir("", "mount-test-source-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(source)
+
+	// Ensure we have a known start point by mounting tmpfs with given options
+	if err := Mount("tmpfs", source, "tmpfs", "private"); err != nil {
+		t.Fatal(err)
+	}
+	defer ensureUnmount(t, source)
+	validateMount(t, source, "", "")
+	if t.Failed() {
+		t.FailNow()
+	}
+
+	target, err := ioutil.TempDir("", "mount-test-target-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(target)
+
+	tests := []struct {
+		source           string
+		ftype            string
+		options          string
+		expectedOpts     string
+		expectedOptional string
+	}{
+		// No options
+		{"tmpfs", "tmpfs", "", "", ""},
+		// Default rw / ro test
+		{source, "", "bind", "", ""},
+		{source, "", "bind,private", "", ""},
+		{source, "", "bind,shared", "", "shared"},
+		{source, "", "bind,slave", "", "master"},
+		{source, "", "bind,unbindable", "", "unbindable"},
+		// Read Write tests
+		{source, "", "bind,rw", "rw", ""},
+		{source, "", "bind,rw,private", "rw", ""},
+		{source, "", "bind,rw,shared", "rw", "shared"},
+		{source, "", "bind,rw,slave", "rw", "master"},
+		{source, "", "bind,rw,unbindable", "rw", "unbindable"},
+		// Read Only tests
+		{source, "", "bind,ro", "ro", ""},
+		{source, "", "bind,ro,private", "ro", ""},
+		{source, "", "bind,ro,shared", "ro", "shared"},
+		{source, "", "bind,ro,slave", "ro", "master"},
+		{source, "", "bind,ro,unbindable", "ro", "unbindable"},
+	}
+
+	for _, tc := range tests {
+		ftype, options := tc.ftype, tc.options
+		if tc.ftype == "" {
+			ftype = "none"
+		}
+		if tc.options == "" {
+			options = "none"
+		}
+
+		t.Run(fmt.Sprintf("%v-%v", ftype, options), func(t *testing.T) {
+			if strings.Contains(tc.options, "slave") {
+				// Slave requires a shared source
+				if err := MakeShared(source); err != nil {
+					t.Fatal(err)
+				}
+				defer func() {
+					if err := MakePrivate(source); err != nil {
+						t.Fatal(err)
+					}
+				}()
+			}
+			if err := Mount(tc.source, target, tc.ftype, tc.options); err != nil {
+				t.Fatal(err)
+			}
+			defer ensureUnmount(t, target)
+			validateMount(t, target, tc.expectedOpts, tc.expectedOptional)
+		})
+	}
+}
+
+// ensureUnmount umounts mnt checking for errors
+func ensureUnmount(t *testing.T, mnt string) {
+	if err := Unmount(mnt); err != nil {
+		t.Error(err)
+	}
+}
+
+// validateMount checks that mnt has the given options
+func validateMount(t *testing.T, mnt string, opts, optional string) {
+	info, err := GetMounts()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	wantedOpts := make(map[string]struct{})
+	if opts != "" {
+		for _, opt := range strings.Split(opts, ",") {
+			wantedOpts[opt] = struct{}{}
+		}
+	}
+
+	wantedOptional := make(map[string]struct{})
+	if optional != "" {
+		for _, opt := range strings.Split(optional, ",") {
+			wantedOptional[opt] = struct{}{}
+		}
+	}
+
+	mnts := make(map[int]*Info, len(info))
+	for _, mi := range info {
+		mnts[mi.ID] = mi
+	}
+
+	for _, mi := range info {
+		if mi.Mountpoint != mnt {
+			continue
+		}
+
+		// Use parent info as the defaults
+		p := mnts[mi.Parent]
+		pOpts := make(map[string]struct{})
+		if p.Opts != "" {
+			for _, opt := range strings.Split(p.Opts, ",") {
+				pOpts[clean(opt)] = struct{}{}
+			}
+		}
+		pOptional := make(map[string]struct{})
+		if p.Optional != "" {
+			for _, field := range strings.Split(p.Optional, ",") {
+				pOptional[clean(field)] = struct{}{}
+			}
+		}
+
+		// Validate Opts
+		if mi.Opts != "" {
+			for _, opt := range strings.Split(mi.Opts, ",") {
+				opt = clean(opt)
+				if !has(wantedOpts, opt) && !has(pOpts, opt) {
+					t.Errorf("unexpected mount option %q expected %q", opt, opts)
+				}
+				delete(wantedOpts, opt)
+			}
+		}
+		for opt := range wantedOpts {
+			t.Errorf("missing mount option %q found %q", opt, mi.Opts)
+		}
+
+		// Validate Optional
+		if mi.Optional != "" {
+			for _, field := range strings.Split(mi.Optional, ",") {
+				field = clean(field)
+				if !has(wantedOptional, field) && !has(pOptional, field) {
+					t.Errorf("unexpected optional failed %q expected %q", field, optional)
+				}
+				delete(wantedOptional, field)
+			}
+		}
+		for field := range wantedOptional {
+			t.Errorf("missing optional field %q found %q", field, mi.Optional)
+		}
+
+		return
+	}
+
+	t.Errorf("failed to find mount %q", mnt)
+}
+
+// clean strips off any value param after the colon
+func clean(v string) string {
+	return strings.SplitN(v, ":", 2)[0]
+}
+
+// has returns true if key is a member of m
+func has(m map[string]struct{}, key string) bool {
+	_, ok := m[key]
+	return ok
+}