Merge pull request #154 from ebiggers/bind-mounts

Store fscrypt metadata in only one place per filesystem, so that bind
mounts don't get their own metadata directories (which was ambiguous,
as the same file may be accessible via multiple mounts).

Also correctly set the source device for root filesystems mounted via
the kernel command line, and fix creating linked protectors to such
filesystems.

actions/context.go

@@ -78,7 +78,7 @@ func NewContextFromPath(path string, target *user.User) (*Context, error) {
 	}
 
 	log.Printf("%s is on %s filesystem %q (%s)", path,
-		ctx.Mount.Filesystem, ctx.Mount.Path, ctx.Mount.Device)
+		ctx.Mount.FilesystemType, ctx.Mount.Path, ctx.Mount.Device)
 	return ctx, nil
 }
 
@@ -95,7 +95,7 @@ func NewContextFromMountpoint(mountpoint string, target *user.User) (*Context, e
 		return nil, err
 	}
 
-	log.Printf("found %s filesystem %q (%s)", ctx.Mount.Filesystem,
+	log.Printf("found %s filesystem %q (%s)", ctx.Mount.FilesystemType,
 		ctx.Mount.Path, ctx.Mount.Device)
 	return ctx, nil
 }
@@ -137,9 +137,9 @@ func (ctx *Context) checkContext() error {
 func (ctx *Context) getService() string {
 	// For legacy configurations, we may need non-standard services
 	if ctx.Config.HasCompatibilityOption(LegacyConfig) {
-		switch ctx.Mount.Filesystem {
+		switch ctx.Mount.FilesystemType {
 		case "ext4", "f2fs":
-			return ctx.Mount.Filesystem + ":"
+			return ctx.Mount.FilesystemType + ":"
 		}
 	}
 	return unix.FS_KEY_DESC_PREFIX

cmd/fscrypt/status.go

@@ -91,8 +91,8 @@ func writeGlobalStatus(w io.Writer) error {
 			continue
 		}
 
-		fmt.Fprintf(t, "%s\t%s\t%s\t%s\t%s\n", mount.Path, mount.Device, mount.Filesystem,
-			supportString, yesNoString(usingFscrypt))
+		fmt.Fprintf(t, "%s\t%s\t%s\t%s\t%s\n", mount.Path, mount.Device,
+			mount.FilesystemType, supportString, yesNoString(usingFscrypt))
 
 		if supportErr == nil {
 			supportCount++
@@ -139,8 +139,9 @@ func writeFilesystemStatus(w io.Writer, ctx *actions.Context) error {
 		return err
 	}
 
-	fmt.Fprintf(w, "%s filesystem %q has %s and %s\n\n", ctx.Mount.Filesystem, ctx.Mount.Path,
-		pluralize(len(options), "protector"), pluralize(len(policyDescriptors), "policy"))
+	fmt.Fprintf(w, "%s filesystem %q has %s and %s\n\n", ctx.Mount.FilesystemType,
+		ctx.Mount.Path, pluralize(len(options), "protector"),
+		pluralize(len(policyDescriptors), "policy"))
 
 	if len(options) > 0 {
 		writeOptions(w, options)

filesystem/filesystem.go

@@ -64,10 +64,15 @@ var (
 )
 
 // Mount contains information for a specific mounted filesystem.
-//	Path       - Absolute path where the directory is mounted
-//	Filesystem - Name of the mounted filesystem
-//	Options    - List of options used when mounting the filesystem
-//	Device     - Device for filesystem (empty string if we cannot find one)
+//	Path           - Absolute path where the directory is mounted
+//	FilesystemType - Type of the mounted filesystem, e.g. "ext4"
+//	Device         - Device for filesystem (empty string if we cannot find one)
+//	DeviceNumber   - Device number of the filesystem.  This is set even if
+//			 Device isn't, since all filesystems have a device
+//			 number assigned by the kernel, even pseudo-filesystems.
+//	BindMnt        - True if this mount is not for the full filesystem but
+//			 rather is only for a subtree.
+//	ReadOnly       - True if this is a read-only mount
 //
 // In order to use a Mount to store fscrypt metadata, some directories must be
 // setup first. Specifically, the directories created look like:
@@ -90,10 +95,12 @@ var (
 // allows login protectors to be created when the root filesystem is read-only,
 // provided that "/.fscrypt" is a symlink pointing to a writable location.
 type Mount struct {
-	Path       string
-	Filesystem string
-	Options    []string
-	Device     string
+	Path           string
+	FilesystemType string
+	Device         string
+	DeviceNumber   DeviceNumber
+	BindMnt        bool
+	ReadOnly       bool
 }
 
 // PathSorter allows mounts to be sorted by Path.
@@ -123,9 +130,8 @@ const (
 
 func (m *Mount) String() string {
 	return fmt.Sprintf(`%s
-	Filsystem: %s
-	Options:   %v
-	Device:    %s`, m.Path, m.Filesystem, m.Options, m.Device)
+	FilesystemType: %s
+	Device:         %s`, m.Path, m.FilesystemType, m.Device)
 }
 
 // BaseDir returns the path to the base fscrypt directory for this filesystem.
@@ -436,21 +442,16 @@ func (m *Mount) GetProtector(descriptor string) (*Mount, *metadata.ProtectorData
 		return nil, nil, m.err(err)
 	}
 
-	// As the link could refer to multiple filesystems, we check each one
-	// for valid metadata.
-	mnts, err := getMountsFromLink(string(link))
+	linkedMnt, err := getMountFromLink(string(link))
 	if err != nil {
 		return nil, nil, m.err(err)
 	}
-
-	for _, mnt := range mnts {
-		if data, err := mnt.GetRegularProtector(descriptor); err != nil {
-			log.Print(err)
-		} else {
-			return mnt, data, nil
-		}
+	data, err := linkedMnt.GetRegularProtector(descriptor)
+	if err != nil {
+		log.Print(err)
+		return nil, nil, m.err(errors.Wrapf(ErrLinkExpired, "protector %s", descriptor))
 	}
-	return nil, nil, m.err(errors.Wrapf(ErrLinkExpired, "protector %s", descriptor))
+	return linkedMnt, data, nil
 }
 
 // RemoveProtector deletes the protector metadata (or a link to another