Merge pull request #41964 from thaJeztah/CVE-2021-21284_master

[master] Fix Access to remapped root allows privilege escalation to real root (CVE-2021-21284)

daemon/container_operations_unix.go

@@ -466,5 +466,5 @@ func (daemon *Daemon) setupContainerMountsRoot(c *container.Container) error {
 	if err != nil {
 		return err
 	}
-	return idtools.MkdirAllAndChown(p, 0700, daemon.idMapping.RootPair())
+	return idtools.MkdirAllAndChown(p, 0701, idtools.CurrentIdentity())
 }

daemon/create.go

@@ -194,12 +194,10 @@ func (daemon *Daemon) create(opts createOpts) (retC *container.Container, retErr
 	}
 	ctr.RWLayer = rwLayer
 
-	rootIDs := daemon.idMapping.RootPair()
-
-	if err := idtools.MkdirAndChown(ctr.Root, 0700, rootIDs); err != nil {
+	if err := idtools.MkdirAndChown(ctr.Root, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
-	if err := idtools.MkdirAndChown(ctr.CheckpointDir(), 0700, rootIDs); err != nil {
+	if err := idtools.MkdirAndChown(ctr.CheckpointDir(), 0700, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 

daemon/daemon.go

@@ -795,7 +795,7 @@ func NewDaemon(ctx context.Context, config *config.Config, pluginStore *plugin.S
 	}
 
 	// set up the tmpDir to use a canonical path
-	tmp, err := prepareTempDir(config.Root, rootIDs)
+	tmp, err := prepareTempDir(config.Root)
 	if err != nil {
 		return nil, fmt.Errorf("Unable to get the TempDir under %s: %s", config.Root, err)
 	}
@@ -861,7 +861,7 @@ func NewDaemon(ctx context.Context, config *config.Config, pluginStore *plugin.S
 	}
 
 	daemonRepo := filepath.Join(config.Root, "containers")
-	if err := idtools.MkdirAllAndChown(daemonRepo, 0700, rootIDs); err != nil {
+	if err := idtools.MkdirAllAndChown(daemonRepo, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -1374,7 +1374,7 @@ func (daemon *Daemon) Subnets() ([]net.IPNet, []net.IPNet) {
 // prepareTempDir prepares and returns the default directory to use
 // for temporary files.
 // If it doesn't exist, it is created. If it exists, its content is removed.
-func prepareTempDir(rootDir string, rootIdentity idtools.Identity) (string, error) {
+func prepareTempDir(rootDir string) (string, error) {
 	var tmpDir string
 	if tmpDir = os.Getenv("DOCKER_TMPDIR"); tmpDir == "" {
 		tmpDir = filepath.Join(rootDir, "tmp")
@@ -1392,9 +1392,7 @@ func prepareTempDir(rootDir string, rootIdentity idtools.Identity) (string, erro
 			}
 		}
 	}
-	// We don't remove the content of tmpdir if it's not the default,
-	// it may hold things that do not belong to us.
-	return tmpDir, idtools.MkdirAllAndChown(tmpDir, 0700, rootIdentity)
+	return tmpDir, idtools.MkdirAllAndChown(tmpDir, 0700, idtools.CurrentIdentity())
 }
 
 func (daemon *Daemon) setGenericResources(conf *config.Config) error {

daemon/daemon_unix.go

@@ -1196,7 +1196,7 @@ func setupRemappedRoot(config *config.Config) (*idtools.IdentityMapping, error)
 	return &idtools.IdentityMapping{}, nil
 }
 
-func setupDaemonRoot(config *config.Config, rootDir string, rootIdentity idtools.Identity) error {
+func setupDaemonRoot(config *config.Config, rootDir string, remappedRoot idtools.Identity) error {
 	config.Root = rootDir
 	// the docker root metadata directory needs to have execute permissions for all users (g+x,o+x)
 	// so that syscalls executing as non-root, operating on subdirectories of the graph root
@@ -1221,10 +1221,16 @@ func setupDaemonRoot(config *config.Config, rootDir string, rootIdentity idtools
 	// a new subdirectory with ownership set to the remapped uid/gid (so as to allow
 	// `chdir()` to work for containers namespaced to that uid/gid)
 	if config.RemappedRoot != "" {
-		config.Root = filepath.Join(rootDir, fmt.Sprintf("%d.%d", rootIdentity.UID, rootIdentity.GID))
+		id := idtools.CurrentIdentity()
+		// First make sure the current root dir has the correct perms.
+		if err := idtools.MkdirAllAndChown(config.Root, 0701, id); err != nil {
+			return errors.Wrapf(err, "could not create or set daemon root permissions: %s", config.Root)
+		}
+
+		config.Root = filepath.Join(rootDir, fmt.Sprintf("%d.%d", remappedRoot.UID, remappedRoot.GID))
 		logrus.Debugf("Creating user namespaced daemon root: %s", config.Root)
 		// Create the root directory if it doesn't exist
-		if err := idtools.MkdirAllAndChown(config.Root, 0700, rootIdentity); err != nil {
+		if err := idtools.MkdirAllAndChown(config.Root, 0701, id); err != nil {
 			return fmt.Errorf("Cannot create daemon root: %s: %v", config.Root, err)
 		}
 		// we also need to verify that any pre-existing directories in the path to
@@ -1237,7 +1243,7 @@ func setupDaemonRoot(config *config.Config, rootDir string, rootIdentity idtools
 			if dirPath == "/" {
 				break
 			}
-			if !idtools.CanAccess(dirPath, rootIdentity) {
+			if !idtools.CanAccess(dirPath, remappedRoot) {
 				return fmt.Errorf("a subdirectory in your graphroot path (%s) restricts access to the remapped root uid/gid; please fix by allowing 'o+x' permissions on existing directories", config.Root)
 			}
 		}

daemon/graphdriver/aufs/aufs.go

@@ -129,18 +129,15 @@ func Init(root string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		locker:    locker.New(),
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, err
-	}
+	currentID := idtools.CurrentIdentity()
 	// Create the root aufs driver dir
-	if err := idtools.MkdirAllAndChown(root, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(root, 0701, currentID); err != nil {
 		return nil, err
 	}
 
 	// Populate the dir structure
 	for _, p := range paths {
-		if err := idtools.MkdirAllAndChown(path.Join(root, p), 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+		if err := idtools.MkdirAllAndChown(path.Join(root, p), 0701, currentID); err != nil {
 			return nil, err
 		}
 	}

daemon/graphdriver/btrfs/btrfs.go

@@ -70,11 +70,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, graphdriver.ErrPrerequisites
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, err
-	}
-	if err := idtools.MkdirAllAndChown(home, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(home, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -525,7 +521,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
 	if err != nil {
 		return err
 	}
-	if err := idtools.MkdirAllAndChown(subvolumes, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(subvolumes, 0701, idtools.CurrentIdentity()); err != nil {
 		return err
 	}
 	if parent == "" {
@@ -560,7 +556,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
 		if err := d.setStorageSize(path.Join(subvolumes, id), driver); err != nil {
 			return err
 		}
-		if err := idtools.MkdirAllAndChown(quotas, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+		if err := idtools.MkdirAllAndChown(quotas, 0700, idtools.CurrentIdentity()); err != nil {
 			return err
 		}
 		if err := ioutil.WriteFile(path.Join(quotas, id), []byte(fmt.Sprint(driver.options.size)), 0644); err != nil {

daemon/graphdriver/fuse-overlayfs/fuseoverlayfs.go

@@ -88,12 +88,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, graphdriver.ErrNotSupported
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, err
-	}
-	// Create the driver home dir
-	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -178,10 +173,11 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 	}
 	root := idtools.Identity{UID: rootUID, GID: rootGID}
 
-	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0700, root); err != nil {
+	currentID := idtools.CurrentIdentity()
+	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0701, currentID); err != nil {
 		return err
 	}
-	if err := idtools.MkdirAndChown(dir, 0700, root); err != nil {
+	if err := idtools.MkdirAndChown(dir, 0701, currentID); err != nil {
 		return err
 	}
 
@@ -215,7 +211,7 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return nil
 	}
 
-	if err := idtools.MkdirAndChown(path.Join(dir, workDirName), 0700, root); err != nil {
+	if err := idtools.MkdirAndChown(path.Join(dir, workDirName), 0701, currentID); err != nil {
 		return err
 	}
 

daemon/graphdriver/overlay/overlay.go

@@ -156,12 +156,8 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		logrus.WithField("storage-driver", "overlay").Warn(overlayutils.ErrDTypeNotSupported("overlay", backingFs))
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, err
-	}
 	// Create the driver home dir
-	if err := idtools.MkdirAllAndChown(home, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(home, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -265,10 +261,11 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 	}
 	root := idtools.Identity{UID: rootUID, GID: rootGID}
 
-	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0700, root); err != nil {
+	currentID := idtools.CurrentIdentity()
+	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0701, currentID); err != nil {
 		return err
 	}
-	if err := idtools.MkdirAndChown(dir, 0700, root); err != nil {
+	if err := idtools.MkdirAndChown(dir, 0701, currentID); err != nil {
 		return err
 	}
 
@@ -281,6 +278,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 
 	// Toplevel images are just a "root" dir
 	if parent == "" {
+		// This must be 0755 otherwise unprivileged users will in the container will not be able to read / in the container
 		return idtools.MkdirAndChown(path.Join(dir, "root"), 0755, root)
 	}
 
@@ -301,7 +299,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		if err := idtools.MkdirAndChown(path.Join(dir, "work"), 0700, root); err != nil {
 			return err
 		}
-		return ioutil.WriteFile(path.Join(dir, "lower-id"), []byte(parent), 0666)
+		return ioutil.WriteFile(path.Join(dir, "lower-id"), []byte(parent), 0600)
 	}
 
 	// Otherwise, copy the upper and the lower-id from the parent
@@ -311,7 +309,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 
-	if err := ioutil.WriteFile(path.Join(dir, "lower-id"), lowerID, 0666); err != nil {
+	if err := ioutil.WriteFile(path.Join(dir, "lower-id"), lowerID, 0600); err != nil {
 		return err
 	}
 

daemon/graphdriver/overlay2/overlay.go

@@ -165,12 +165,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		logger.Warn(overlayutils.ErrDTypeNotSupported("overlay2", backingFs))
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, err
-	}
-	// Create the driver home dir
-	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -339,11 +334,12 @@ func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts) (retErr
 		return err
 	}
 	root := idtools.Identity{UID: rootUID, GID: rootGID}
+	current := idtools.CurrentIdentity()
 
-	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0700, root); err != nil {
+	if err := idtools.MkdirAllAndChown(path.Dir(dir), 0701, current); err != nil {
 		return err
 	}
-	if err := idtools.MkdirAndChown(dir, 0700, root); err != nil {
+	if err := idtools.MkdirAndChown(dir, 0701, current); err != nil {
 		return err
 	}
 

daemon/graphdriver/vfs/driver.go

@@ -38,8 +38,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, err
 	}
 
-	rootIDs := d.idMapping.RootPair()
-	if err := idtools.MkdirAllAndChown(home, 0700, rootIDs); err != nil {
+	if err := idtools.MkdirAllAndChown(home, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, err
 	}
 
@@ -141,7 +140,7 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
 func (d *Driver) create(id, parent string, size uint64) error {
 	dir := d.dir(id)
 	rootIDs := d.idMapping.RootPair()
-	if err := idtools.MkdirAllAndChown(filepath.Dir(dir), 0700, rootIDs); err != nil {
+	if err := idtools.MkdirAllAndChown(filepath.Dir(dir), 0701, idtools.CurrentIdentity()); err != nil {
 		return err
 	}
 	if err := idtools.MkdirAndChown(dir, 0755, rootIDs); err != nil {

daemon/graphdriver/zfs/zfs.go

@@ -104,11 +104,7 @@ func Init(base string, opt []string, uidMaps, gidMaps []idtools.IDMap) (graphdri
 		return nil, fmt.Errorf("BUG: zfs get all -t filesystem -rHp '%s' should contain '%s'", options.fsName, options.fsName)
 	}
 
-	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)
-	if err != nil {
-		return nil, fmt.Errorf("Failed to get root uid/guid: %v", err)
-	}
-	if err := idtools.MkdirAllAndChown(base, 0700, idtools.Identity{UID: rootUID, GID: rootGID}); err != nil {
+	if err := idtools.MkdirAllAndChown(base, 0701, idtools.CurrentIdentity()); err != nil {
 		return nil, fmt.Errorf("Failed to create '%s': %v", base, err)
 	}
 

pkg/idtools/idtools.go

@@ -35,13 +35,13 @@ const (
 
 // MkdirAllAndChown creates a directory (include any along the path) and then modifies
 // ownership to the requested uid/gid.  If the directory already exists, this
-// function will still change ownership to the requested uid/gid pair.
+// function will still change ownership and permissions.
 func MkdirAllAndChown(path string, mode os.FileMode, owner Identity) error {
 	return mkdirAs(path, mode, owner, true, true)
 }
 
 // MkdirAndChown creates a directory and then modifies ownership to the requested uid/gid.
-// If the directory already exists, this function still changes ownership.
+// If the directory already exists, this function still changes ownership and permissions.
 // Note that unlike os.Mkdir(), this function does not return IsExist error
 // in case path already exists.
 func MkdirAndChown(path string, mode os.FileMode, owner Identity) error {
@@ -50,7 +50,7 @@ func MkdirAndChown(path string, mode os.FileMode, owner Identity) error {
 
 // MkdirAllAndChownNew creates a directory (include any along the path) and then modifies
 // ownership ONLY of newly created directories to the requested uid/gid. If the
-// directories along the path exist, no change of ownership will be performed
+// directories along the path exist, no change of ownership or permissions will be performed
 func MkdirAllAndChownNew(path string, mode os.FileMode, owner Identity) error {
 	return mkdirAs(path, mode, owner, true, false)
 }
@@ -234,3 +234,8 @@ func parseSubidFile(path, username string) (ranges, error) {
 
 	return rangeList, s.Err()
 }
+
+// CurrentIdentity returns the identity of the current process
+func CurrentIdentity() Identity {
+	return Identity{UID: os.Getuid(), GID: os.Getegid()}
+}

pkg/idtools/idtools_unix.go

@@ -40,7 +40,7 @@ func mkdirAs(path string, mode os.FileMode, owner Identity, mkAll, chownExisting
 		}
 
 		// short-circuit--we were called with an existing directory and chown was requested
-		return lazyChown(path, owner.UID, owner.GID, stat)
+		return setPermissions(path, mode, owner.UID, owner.GID, stat)
 	}
 
 	if os.IsNotExist(err) {
@@ -71,7 +71,7 @@ func mkdirAs(path string, mode os.FileMode, owner Identity, mkAll, chownExisting
 	// even if it existed, we will chown the requested path + any subpaths that
 	// didn't exist when we called MkdirAll
 	for _, pathComponent := range paths {
-		if err := lazyChown(pathComponent, owner.UID, owner.GID, nil); err != nil {
+		if err := setPermissions(pathComponent, mode, owner.UID, owner.GID, nil); err != nil {
 			return err
 		}
 	}
@@ -213,17 +213,23 @@ func callGetent(database, key string) (io.Reader, error) {
 	return bytes.NewReader(out), nil
 }
 
-// lazyChown performs a chown only if the uid/gid don't match what's requested
+// setPermissions performs a chown/chmod only if the uid/gid don't match what's requested
 // Normally a Chown is a no-op if uid/gid match, but in some cases this can still cause an error, e.g. if the
 // dir is on an NFS share, so don't call chown unless we absolutely must.
-func lazyChown(p string, uid, gid int, stat *system.StatT) error {
+// Likewise for setting permissions.
+func setPermissions(p string, mode os.FileMode, uid, gid int, stat *system.StatT) error {
 	if stat == nil {
 		var err error
 		stat, err = system.Stat(p)
 		if err != nil {
 			return err
 		}
 	}
+	if os.FileMode(stat.Mode()).Perm() != mode.Perm() {
+		if err := os.Chmod(p, mode.Perm()); err != nil {
+			return err
+		}
+	}
 	if stat.UID() == uint32(uid) && stat.GID() == uint32(gid) {
 		return nil
 	}