Add support for sentry internal pipe for gofer mounts

Internal pipes are supported similarly to how internal UDS is done.
It is also controlled by the same flag.

Fixes #1102

PiperOrigin-RevId: 293150045

8 files changed, 293 insertions, 140 deletions

diff --git a/pkg/sentry/fs/gofer/BUILD b/pkg/sentry/fs/gofer/BUILD
index 971d3718e..fea135eea 100644
--- a/pkg/sentry/fs/gofer/BUILD
+++ b/pkg/sentry/fs/gofer/BUILD
@@ -9,6 +9,7 @@ go_library(
         "cache_policy.go",
         "context_file.go",
         "device.go",
+        "fifo.go",
         "file.go",
         "file_state.go",
         "fs.go",
@@ -38,6 +39,7 @@ go_library(
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/host",
         "//pkg/sentry/kernel/auth",
+        "//pkg/sentry/kernel/pipe",
         "//pkg/sentry/kernel/time",
         "//pkg/sentry/memmap",
         "//pkg/sentry/socket/unix/transport",
diff --git a/pkg/sentry/fs/gofer/cache_policy.go b/pkg/sentry/fs/gofer/cache_policy.go
index ebea03c42..07a564e92 100644
--- a/pkg/sentry/fs/gofer/cache_policy.go
+++ b/pkg/sentry/fs/gofer/cache_policy.go
@@ -127,6 +127,9 @@ func (cp cachePolicy) revalidate(ctx context.Context, name string, parent, child
 
 	childIops, ok := child.InodeOperations.(*inodeOperations)
 	if !ok {
+		if _, ok := child.InodeOperations.(*fifo); ok {
+			return false
+		}
 		panic(fmt.Sprintf("revalidating inode operations of unknown type %T", child.InodeOperations))
 	}
 	parentIops, ok := parent.InodeOperations.(*inodeOperations)
diff --git a/pkg/sentry/fs/gofer/fifo.go b/pkg/sentry/fs/gofer/fifo.go
new file mode 100644
index 000000000..456557058
--- /dev/null
+++ b/pkg/sentry/fs/gofer/fifo.go
@@ -0,0 +1,40 @@
+// Copyright 2020 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 gofer
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
+)
+
+// +stateify savable
+type fifo struct {
+	fs.InodeOperations
+	fileIops *inodeOperations
+}
+
+var _ fs.InodeOperations = (*fifo)(nil)
+
+// Rename implements fs.InodeOperations. It forwards the call to the underlying
+// file inode to handle the file rename. Note that file key remains the same
+// after the rename to keep the endpoint mapping.
+func (i *fifo) Rename(ctx context.Context, inode *fs.Inode, oldParent *fs.Inode, oldName string, newParent *fs.Inode, newName string, replacement bool) error {
+	return i.fileIops.Rename(ctx, inode, oldParent, oldName, newParent, newName, replacement)
+}
+
+// StatFS implements fs.InodeOperations.
+func (i *fifo) StatFS(ctx context.Context) (fs.Info, error) {
+	return i.fileIops.StatFS(ctx)
+}
diff --git a/pkg/sentry/fs/gofer/gofer_test.go b/pkg/sentry/fs/gofer/gofer_test.go
index 0c2f89ae8..2df2fe889 100644
--- a/pkg/sentry/fs/gofer/gofer_test.go
+++ b/pkg/sentry/fs/gofer/gofer_test.go
@@ -61,7 +61,7 @@ func rootTest(t *testing.T, name string, cp cachePolicy, fn func(context.Context
 		ctx := contexttest.Context(t)
 		sattr, rootInodeOperations := newInodeOperations(ctx, s, contextFile{
 			file: rootFile,
-		}, root.QID, p9.AttrMaskAll(), root.Attr, false /* socket */)
+		}, root.QID, p9.AttrMaskAll(), root.Attr)
 		m := fs.NewMountSource(ctx, s, &filesystem{}, fs.MountSourceFlags{})
 		rootInode := fs.NewInode(ctx, rootInodeOperations, m, sattr)
 
diff --git a/pkg/sentry/fs/gofer/path.go b/pkg/sentry/fs/gofer/path.go
index 0c1be05ef..a35c3a23d 100644
--- a/pkg/sentry/fs/gofer/path.go
+++ b/pkg/sentry/fs/gofer/path.go
@@ -23,14 +23,24 @@ import (
 	"gvisor.dev/gvisor/pkg/p9"
 	"gvisor.dev/gvisor/pkg/sentry/device"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/pipe"
 	"gvisor.dev/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
 )
 
 // maxFilenameLen is the maximum length of a filename. This is dictated by 9P's
 // encoding of strings, which uses 2 bytes for the length prefix.
 const maxFilenameLen = (1 << 16) - 1
 
+func changeType(mode p9.FileMode, newType p9.FileMode) p9.FileMode {
+	if newType&^p9.FileModeMask != 0 {
+		panic(fmt.Sprintf("newType contained more bits than just file mode: %x", newType))
+	}
+	clear := mode &^ p9.FileModeMask
+	return clear | newType
+}
+
 // Lookup loads an Inode at name into a Dirent based on the session's cache
 // policy.
 func (i *inodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string) (*fs.Dirent, error) {
@@ -69,8 +79,25 @@ func (i *inodeOperations) Lookup(ctx context.Context, dir *fs.Inode, name string
 		return nil, err
 	}
 
+	if i.session().overrides != nil {
+		// Check if file belongs to a internal named pipe. Note that it doesn't need
+		// to check for sockets because it's done in newInodeOperations below.
+		deviceKey := device.MultiDeviceKey{
+			Device:          p9attr.RDev,
+			SecondaryDevice: i.session().connID,
+			Inode:           qids[0].Path,
+		}
+		unlock := i.session().overrides.lock()
+		if pipeInode := i.session().overrides.getPipe(deviceKey); pipeInode != nil {
+			unlock()
+			pipeInode.IncRef()
+			return fs.NewDirent(ctx, pipeInode, name), nil
+		}
+		unlock()
+	}
+
 	// Construct the Inode operations.
-	sattr, node := newInodeOperations(ctx, i.fileState.s, newFile, qids[0], mask, p9attr, false)
+	sattr, node := newInodeOperations(ctx, i.fileState.s, newFile, qids[0], mask, p9attr)
 
 	// Construct a positive Dirent.
 	return fs.NewDirent(ctx, fs.NewInode(ctx, node, dir.MountSource, sattr), name), nil
@@ -138,7 +165,7 @@ func (i *inodeOperations) Create(ctx context.Context, dir *fs.Inode, name string
 	qid := qids[0]
 
 	// Construct the InodeOperations.
-	sattr, iops := newInodeOperations(ctx, i.fileState.s, unopened, qid, mask, p9attr, false)
+	sattr, iops := newInodeOperations(ctx, i.fileState.s, unopened, qid, mask, p9attr)
 
 	// Construct the positive Dirent.
 	d := fs.NewDirent(ctx, fs.NewInode(ctx, iops, dir.MountSource, sattr), name)
@@ -223,82 +250,115 @@ func (i *inodeOperations) Bind(ctx context.Context, dir *fs.Inode, name string,
 		return nil, syserror.ENAMETOOLONG
 	}
 
-	if i.session().endpoints == nil {
+	if i.session().overrides == nil {
 		return nil, syscall.EOPNOTSUPP
 	}
 
-	// Create replaces the directory fid with the newly created/opened
-	// file, so clone this directory so it doesn't change out from under
-	// this node.
-	_, newFile, err := i.fileState.file.walk(ctx, nil)
+	// Stabilize the override map while creation is in progress.
+	unlock := i.session().overrides.lock()
+	defer unlock()
+
+	sattr, iops, err := i.createEndpointFile(ctx, dir, name, perm, p9.ModeSocket)
 	if err != nil {
 		return nil, err
 	}
-	// We're not going to use newFile after return.
-	defer newFile.close(ctx)
 
-	// Stabilize the endpoint map while creation is in progress.
-	unlock := i.session().endpoints.lock()
-	defer unlock()
+	// Construct the positive Dirent.
+	childDir := fs.NewDirent(ctx, fs.NewInode(ctx, iops, dir.MountSource, sattr), name)
+	i.session().overrides.addBoundEndpoint(iops.fileState.key, childDir, ep)
+	return childDir, nil
+}
 
-	// Create a regular file in the gofer and then mark it as a socket by
-	// adding this inode key in the 'endpoints' map.
-	owner := fs.FileOwnerFromContext(ctx)
-	hostFile, err := newFile.create(ctx, name, p9.ReadWrite, p9.FileMode(perm.LinuxMode()), p9.UID(owner.UID), p9.GID(owner.GID))
-	if err != nil {
-		return nil, err
+// CreateFifo implements fs.InodeOperations.CreateFifo.
+func (i *inodeOperations) CreateFifo(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions) error {
+	if len(name) > maxFilenameLen {
+		return syserror.ENAMETOOLONG
 	}
-	// We're not going to use this file.
-	hostFile.Close()
 
-	i.touchModificationAndStatusChangeTime(ctx, dir)
+	owner := fs.FileOwnerFromContext(ctx)
+	mode := p9.FileMode(perm.LinuxMode()) | p9.ModeNamedPipe
 
-	// Get the attributes of the file to create inode key.
-	qid, mask, attr, err := getattr(ctx, newFile)
-	if err != nil {
-		return nil, err
+	// N.B. FIFOs use major/minor numbers 0.
+	if _, err := i.fileState.file.mknod(ctx, name, mode, 0, 0, p9.UID(owner.UID), p9.GID(owner.GID)); err != nil {
+		if i.session().overrides == nil || err != syscall.EPERM {
+			return err
+		}
+		// If gofer doesn't support mknod, check if we can create an internal fifo.
+		return i.createInternalFifo(ctx, dir, name, owner, perm)
 	}
 
-	key := device.MultiDeviceKey{
-		Device:          attr.RDev,
-		SecondaryDevice: i.session().connID,
-		Inode:           qid.Path,
+	i.touchModificationAndStatusChangeTime(ctx, dir)
+	return nil
+}
+
+func (i *inodeOperations) createInternalFifo(ctx context.Context, dir *fs.Inode, name string, owner fs.FileOwner, perm fs.FilePermissions) error {
+	if i.session().overrides == nil {
+		return syserror.EPERM
 	}
 
-	// Create child dirent.
+	// Stabilize the override map while creation is in progress.
+	unlock := i.session().overrides.lock()
+	defer unlock()
 
-	// Get an unopened p9.File for the file we created so that it can be
-	// cloned and re-opened multiple times after creation.
-	_, unopened, err := i.fileState.file.walk(ctx, []string{name})
+	sattr, fileOps, err := i.createEndpointFile(ctx, dir, name, perm, p9.ModeNamedPipe)
 	if err != nil {
-		return nil, err
+		return err
 	}
 
-	// Construct the InodeOperations.
-	sattr, iops := newInodeOperations(ctx, i.fileState.s, unopened, qid, mask, attr, true)
+	// First create a pipe.
+	p := pipe.NewPipe(true /* isNamed */, pipe.DefaultPipeSize, usermem.PageSize)
+
+	// Wrap the fileOps with our Fifo.
+	iops := &fifo{
+		InodeOperations: pipe.NewInodeOperations(ctx, perm, p),
+		fileIops:        fileOps,
+	}
+	inode := fs.NewInode(ctx, iops, dir.MountSource, sattr)
 
 	// Construct the positive Dirent.
 	childDir := fs.NewDirent(ctx, fs.NewInode(ctx, iops, dir.MountSource, sattr), name)
-	i.session().endpoints.add(key, childDir, ep)
-	return childDir, nil
+	i.session().overrides.addPipe(fileOps.fileState.key, childDir, inode)
+	return nil
 }
 
-// CreateFifo implements fs.InodeOperations.CreateFifo.
-func (i *inodeOperations) CreateFifo(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions) error {
-	if len(name) > maxFilenameLen {
-		return syserror.ENAMETOOLONG
+// Caller must hold Session.endpoint lock.
+func (i *inodeOperations) createEndpointFile(ctx context.Context, dir *fs.Inode, name string, perm fs.FilePermissions, fileType p9.FileMode) (fs.StableAttr, *inodeOperations, error) {
+	_, dirClone, err := i.fileState.file.walk(ctx, nil)
+	if err != nil {
+		return fs.StableAttr{}, nil, err
 	}
+	// We're not going to use dirClone after return.
+	defer dirClone.close(ctx)
 
+	// Create a regular file in the gofer and then mark it as a socket by
+	// adding this inode key in the 'overrides' map.
 	owner := fs.FileOwnerFromContext(ctx)
-	mode := p9.FileMode(perm.LinuxMode()) | p9.ModeNamedPipe
-
-	// N.B. FIFOs use major/minor numbers 0.
-	if _, err := i.fileState.file.mknod(ctx, name, mode, 0, 0, p9.UID(owner.UID), p9.GID(owner.GID)); err != nil {
-		return err
+	hostFile, err := dirClone.create(ctx, name, p9.ReadWrite, p9.FileMode(perm.LinuxMode()), p9.UID(owner.UID), p9.GID(owner.GID))
+	if err != nil {
+		return fs.StableAttr{}, nil, err
 	}
+	// We're not going to use this file.
+	hostFile.Close()
 
 	i.touchModificationAndStatusChangeTime(ctx, dir)
-	return nil
+
+	// Get the attributes of the file to create inode key.
+	qid, mask, attr, err := getattr(ctx, dirClone)
+	if err != nil {
+		return fs.StableAttr{}, nil, err
+	}
+
+	// Get an unopened p9.File for the file we created so that it can be
+	// cloned and re-opened multiple times after creation.
+	_, unopened, err := i.fileState.file.walk(ctx, []string{name})
+	if err != nil {
+		return fs.StableAttr{}, nil, err
+	}
+
+	// Construct new inode with file type overridden.
+	attr.Mode = changeType(attr.Mode, fileType)
+	sattr, iops := newInodeOperations(ctx, i.fileState.s, unopened, qid, mask, attr)
+	return sattr, iops, nil
 }
 
 // Remove implements InodeOperations.Remove.
@@ -307,20 +367,23 @@ func (i *inodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string
 		return syserror.ENAMETOOLONG
 	}
 
-	var key device.MultiDeviceKey
-	removeSocket := false
-	if i.session().endpoints != nil {
-		// Find out if file being deleted is a socket that needs to be
+	var key *device.MultiDeviceKey
+	if i.session().overrides != nil {
+		// Find out if file being deleted is a socket or pipe that needs to be
 		// removed from endpoint map.
 		if d, err := i.Lookup(ctx, dir, name); err == nil {
 			defer d.DecRef()
-			if fs.IsSocket(d.Inode.StableAttr) {
-				child := d.Inode.InodeOperations.(*inodeOperations)
-				key = child.fileState.key
-				removeSocket = true
 
-				// Stabilize the endpoint map while deletion is in progress.
-				unlock := i.session().endpoints.lock()
+			if fs.IsSocket(d.Inode.StableAttr) || fs.IsPipe(d.Inode.StableAttr) {
+				switch iops := d.Inode.InodeOperations.(type) {
+				case *inodeOperations:
+					key = &iops.fileState.key
+				case *fifo:
+					key = &iops.fileIops.fileState.key
+				}
+
+				// Stabilize the override map while deletion is in progress.
+				unlock := i.session().overrides.lock()
 				defer unlock()
 			}
 		}
@@ -329,8 +392,8 @@ func (i *inodeOperations) Remove(ctx context.Context, dir *fs.Inode, name string
 	if err := i.fileState.file.unlinkAt(ctx, name, 0); err != nil {
 		return err
 	}
-	if removeSocket {
-		i.session().endpoints.remove(key)
+	if key != nil {
+		i.session().overrides.remove(*key)
 	}
 	i.touchModificationAndStatusChangeTime(ctx, dir)
 
diff --git a/pkg/sentry/fs/gofer/session.go b/pkg/sentry/fs/gofer/session.go
index 498c4645a..f6b3ef178 100644
--- a/pkg/sentry/fs/gofer/session.go
+++ b/pkg/sentry/fs/gofer/session.go
@@ -33,60 +33,107 @@ import (
 var DefaultDirentCacheSize uint64 = fs.DefaultDirentCacheSize
 
 // +stateify savable
-type endpointMaps struct {
-	// mu protexts the direntMap, the keyMap, and the pathMap below.
-	mu sync.RWMutex `state:"nosave"`
+type overrideInfo struct {
+	dirent *fs.Dirent
+
+	// endpoint is set when dirent points to a socket. inode must not be set.
+	endpoint transport.BoundEndpoint
+
+	// inode is set when dirent points to a pipe. endpoint must not be set.
+	inode *fs.Inode
+}
 
-	// direntMap links sockets to their dirents.
-	// It is filled concurrently with the keyMap and is stored upon save.
-	// Before saving, this map is used to populate the pathMap.
-	direntMap map[transport.BoundEndpoint]*fs.Dirent
+func (l *overrideInfo) inodeType() fs.InodeType {
+	switch {
+	case l.endpoint != nil:
+		return fs.Socket
+	case l.inode != nil:
+		return fs.Pipe
+	}
+	panic("endpoint or node must be set")
+}
 
-	// keyMap links MultiDeviceKeys (containing inode IDs) to their sockets.
+// +stateify savable
+type overrideMaps struct {
+	// mu protexts the keyMap, and the pathMap below.
+	mu sync.RWMutex `state:"nosave"`
+
+	// keyMap links MultiDeviceKeys (containing inode IDs) to their sockets/pipes.
 	// It is not stored during save because the inode ID may change upon restore.
-	keyMap map[device.MultiDeviceKey]transport.BoundEndpoint `state:"nosave"`
+	keyMap map[device.MultiDeviceKey]*overrideInfo `state:"nosave"`
 
-	// pathMap links the sockets to their paths.
+	// pathMap links the sockets/pipes to their paths.
 	// It is filled before saving from the direntMap and is stored upon save.
 	// Upon restore, this map is used to re-populate the keyMap.
-	pathMap map[transport.BoundEndpoint]string
+	pathMap map[*overrideInfo]string
+}
+
+// addBoundEndpoint adds the bound endpoint to the map.
+// A reference is taken on the dirent argument.
+//
+// Precondition: maps must have been locked with 'lock'.
+func (e *overrideMaps) addBoundEndpoint(key device.MultiDeviceKey, d *fs.Dirent, ep transport.BoundEndpoint) {
+	d.IncRef()
+	e.keyMap[key] = &overrideInfo{dirent: d, endpoint: ep}
 }
 
-// add adds the endpoint to the maps.
+// addPipe adds the pipe inode to the map.
 // A reference is taken on the dirent argument.
 //
 // Precondition: maps must have been locked with 'lock'.
-func (e *endpointMaps) add(key device.MultiDeviceKey, d *fs.Dirent, ep transport.BoundEndpoint) {
-	e.keyMap[key] = ep
+func (e *overrideMaps) addPipe(key device.MultiDeviceKey, d *fs.Dirent, inode *fs.Inode) {
 	d.IncRef()
-	e.direntMap[ep] = d
+	e.keyMap[key] = &overrideInfo{dirent: d, inode: inode}
 }
 
 // remove deletes the key from the maps.
 //
 // Precondition: maps must have been locked with 'lock'.
-func (e *endpointMaps) remove(key device.MultiDeviceKey) {
-	endpoint := e.get(key)
+func (e *overrideMaps) remove(key device.MultiDeviceKey) {
+	endpoint := e.keyMap[key]
 	delete(e.keyMap, key)
-
-	d := e.direntMap[endpoint]
-	d.DecRef()
-	delete(e.direntMap, endpoint)
+	endpoint.dirent.DecRef()
 }
 
 // lock blocks other addition and removal operations from happening while
 // the backing file is being created or deleted. Returns a function that unlocks
 // the endpoint map.
-func (e *endpointMaps) lock() func() {
+func (e *overrideMaps) lock() func() {
 	e.mu.Lock()
 	return func() { e.mu.Unlock() }
 }
 
-// get returns the endpoint mapped to the given key.
+// getBoundEndpoint returns the bound endpoint mapped to the given key.
 //
-// Precondition: maps must have been locked for reading.
-func (e *endpointMaps) get(key device.MultiDeviceKey) transport.BoundEndpoint {
-	return e.keyMap[key]
+// Precondition: maps must have been locked.
+func (e *overrideMaps) getBoundEndpoint(key device.MultiDeviceKey) transport.BoundEndpoint {
+	if v := e.keyMap[key]; v != nil {
+		return v.endpoint
+	}
+	return nil
+}
+
+// getPipe returns the pipe inode mapped to the given key.
+//
+// Precondition: maps must have been locked.
+func (e *overrideMaps) getPipe(key device.MultiDeviceKey) *fs.Inode {
+	if v := e.keyMap[key]; v != nil {
+		return v.inode
+	}
+	return nil
+}
+
+// getType returns the inode type if there is a corresponding endpoint for the
+// given key. Returns false otherwise.
+func (e *overrideMaps) getType(key device.MultiDeviceKey) (fs.InodeType, bool) {
+	e.mu.Lock()
+	v := e.keyMap[key]
+	e.mu.Unlock()
+
+	if v != nil {
+		return v.inodeType(), true
+	}
+	return 0, false
 }
 
 // session holds state for each 9p session established during sys_mount.
@@ -137,16 +184,16 @@ type session struct {
 	// mounter is the EUID/EGID that mounted this file system.
 	mounter fs.FileOwner `state:"wait"`
 
-	// endpoints is used to map inodes that represent socket files to their
-	// corresponding endpoint. Socket files are created as regular files in the
-	// gofer and their presence in this map indicate that they should indeed be
-	// socket files. This allows unix domain sockets to be used with paths that
-	// belong to a gofer.
+	// overrides is used to map inodes that represent socket/pipes files to their
+	// corresponding endpoint/iops. These files are created as regular files in
+	// the gofer and their presence in this map indicate that they should indeed
+	// be socket/pipe files. This allows unix domain sockets and named pipes to
+	// be used with paths that belong to a gofer.
 	//
 	// TODO(gvisor.dev/issue/1200): there are few possible races with someone
 	// stat'ing the file and another deleting it concurrently, where the file
 	// will not be reported as socket file.
-	endpoints *endpointMaps `state:"wait"`
+	overrides *overrideMaps `state:"wait"`
 }
 
 // Destroy tears down the session.
@@ -179,15 +226,21 @@ func (s *session) SaveInodeMapping(inode *fs.Inode, path string) {
 	// This is very unintuitive. We *CANNOT* trust the inode's StableAttrs,
 	// because overlay copyUp may have changed them out from under us.
 	// So much for "immutable".
-	sattr := inode.InodeOperations.(*inodeOperations).fileState.sattr
-	s.inodeMappings[sattr.InodeID] = path
+	switch iops := inode.InodeOperations.(type) {
+	case *inodeOperations:
+		s.inodeMappings[iops.fileState.sattr.InodeID] = path
+	case *fifo:
+		s.inodeMappings[iops.fileIops.fileState.sattr.InodeID] = path
+	default:
+		panic(fmt.Sprintf("Invalid type: %T", iops))
+	}
 }
 
-// newInodeOperations creates a new 9p fs.InodeOperations backed by a p9.File and attributes
-// (p9.QID, p9.AttrMask, p9.Attr).
+// newInodeOperations creates a new 9p fs.InodeOperations backed by a p9.File
+// and attributes (p9.QID, p9.AttrMask, p9.Attr).
 //
 // Endpoints lock must not be held if socket == false.
-func newInodeOperations(ctx context.Context, s *session, file contextFile, qid p9.QID, valid p9.AttrMask, attr p9.Attr, socket bool) (fs.StableAttr, *inodeOperations) {
+func newInodeOperations(ctx context.Context, s *session, file contextFile, qid p9.QID, valid p9.AttrMask, attr p9.Attr) (fs.StableAttr, *inodeOperations) {
 	deviceKey := device.MultiDeviceKey{
 		Device:          attr.RDev,
 		SecondaryDevice: s.connID,
@@ -201,17 +254,11 @@ func newInodeOperations(ctx context.Context, s *session, file contextFile, qid p
 		BlockSize: bsize(attr),
 	}
 
-	if s.endpoints != nil {
-		if socket {
-			sattr.Type = fs.Socket
-		} else {
-			// If unix sockets are allowed on this filesystem, check if this file is
-			// supposed to be a socket file.
-			unlock := s.endpoints.lock()
-			if s.endpoints.get(deviceKey) != nil {
-				sattr.Type = fs.Socket
-			}
-			unlock()
+	if s.overrides != nil && sattr.Type == fs.RegularFile {
+		// If overrides are allowed on this filesystem, check if this file is
+		// supposed to be of a different type, e.g. socket.
+		if t, ok := s.overrides.getType(deviceKey); ok {
+			sattr.Type = t
 		}
 	}
 
@@ -267,7 +314,7 @@ func Root(ctx context.Context, dev string, filesystem fs.Filesystem, superBlockF
 	s.EnableLeakCheck("gofer.session")
 
 	if o.privateunixsocket {
-		s.endpoints = newEndpointMaps()
+		s.overrides = newOverrideMaps()
 	}
 
 	// Construct the MountSource with the session and superBlockFlags.
@@ -305,26 +352,24 @@ func Root(ctx context.Context, dev string, filesystem fs.Filesystem, superBlockF
 		return nil, err
 	}
 
-	sattr, iops := newInodeOperations(ctx, &s, s.attach, qid, valid, attr, false)
+	sattr, iops := newInodeOperations(ctx, &s, s.attach, qid, valid, attr)
 	return fs.NewInode(ctx, iops, m, sattr), nil
 }
 
-// newEndpointMaps creates a new endpointMaps.
-func newEndpointMaps() *endpointMaps {
-	return &endpointMaps{
-		direntMap: make(map[transport.BoundEndpoint]*fs.Dirent),
-		keyMap:    make(map[device.MultiDeviceKey]transport.BoundEndpoint),
-		pathMap:   make(map[transport.BoundEndpoint]string),
+// newOverrideMaps creates a new overrideMaps.
+func newOverrideMaps() *overrideMaps {
+	return &overrideMaps{
+		keyMap:  make(map[device.MultiDeviceKey]*overrideInfo),
+		pathMap: make(map[*overrideInfo]string),
 	}
 }
 
-// fillKeyMap populates key and dirent maps upon restore from saved
-// pathmap.
+// fillKeyMap populates key and dirent maps upon restore from saved pathmap.
 func (s *session) fillKeyMap(ctx context.Context) error {
-	unlock := s.endpoints.lock()
+	unlock := s.overrides.lock()
 	defer unlock()
 
-	for ep, dirPath := range s.endpoints.pathMap {
+	for ep, dirPath := range s.overrides.pathMap {
 		_, file, err := s.attach.walk(ctx, splitAbsolutePath(dirPath))
 		if err != nil {
 			return fmt.Errorf("error filling endpointmaps, failed to walk to %q: %v", dirPath, err)
@@ -341,25 +386,25 @@ func (s *session) fillKeyMap(ctx context.Context) error {
 			Inode:           qid.Path,
 		}
 
-		s.endpoints.keyMap[key] = ep
+		s.overrides.keyMap[key] = ep
 	}
 	return nil
 }
 
-// fillPathMap populates paths for endpoints from dirents in direntMap
+// fillPathMap populates paths for overrides from dirents in direntMap
 // before save.
 func (s *session) fillPathMap() error {
-	unlock := s.endpoints.lock()
+	unlock := s.overrides.lock()
 	defer unlock()
 
-	for ep, dir := range s.endpoints.direntMap {
-		mountRoot := dir.MountRoot()
+	for _, endpoint := range s.overrides.keyMap {
+		mountRoot := endpoint.dirent.MountRoot()
 		defer mountRoot.DecRef()
-		dirPath, _ := dir.FullName(mountRoot)
+		dirPath, _ := endpoint.dirent.FullName(mountRoot)
 		if dirPath == "" {
 			return fmt.Errorf("error getting path from dirent")
 		}
-		s.endpoints.pathMap[ep] = dirPath
+		s.overrides.pathMap[endpoint] = dirPath
 	}
 	return nil
 }
@@ -368,7 +413,7 @@ func (s *session) fillPathMap() error {
 func (s *session) restoreEndpointMaps(ctx context.Context) error {
 	// When restoring, only need to create the keyMap because the dirent and path
 	// maps got stored through the save.
-	s.endpoints.keyMap = make(map[device.MultiDeviceKey]transport.BoundEndpoint)
+	s.overrides.keyMap = make(map[device.MultiDeviceKey]*overrideInfo)
 	if err := s.fillKeyMap(ctx); err != nil {
 		return fmt.Errorf("failed to insert sockets into endpoint map: %v", err)
 	}
@@ -376,6 +421,6 @@ func (s *session) restoreEndpointMaps(ctx context.Context) error {
 	// Re-create pathMap because it can no longer be trusted as socket paths can
 	// change while process continues to run. Empty pathMap will be re-filled upon
 	// next save.
-	s.endpoints.pathMap = make(map[transport.BoundEndpoint]string)
+	s.overrides.pathMap = make(map[*overrideInfo]string)
 	return nil
 }
diff --git a/pkg/sentry/fs/gofer/session_state.go b/pkg/sentry/fs/gofer/session_state.go
index 0285c5361..111da59f9 100644
--- a/pkg/sentry/fs/gofer/session_state.go
+++ b/pkg/sentry/fs/gofer/session_state.go
@@ -25,9 +25,9 @@ import (
 
 // beforeSave is invoked by stateify.
 func (s *session) beforeSave() {
-	if s.endpoints != nil {
+	if s.overrides != nil {
 		if err := s.fillPathMap(); err != nil {
-			panic("failed to save paths to endpoint map before saving" + err.Error())
+			panic("failed to save paths to override map before saving" + err.Error())
 		}
 	}
 }
@@ -74,10 +74,10 @@ func (s *session) afterLoad() {
 		panic(fmt.Sprintf("new attach name %v, want %v", opts.aname, s.aname))
 	}
 
-	// Check if endpointMaps exist when uds sockets are enabled
-	// (only pathmap will actualy have been saved).
-	if opts.privateunixsocket != (s.endpoints != nil) {
-		panic(fmt.Sprintf("new privateunixsocket option %v, want %v", opts.privateunixsocket, s.endpoints != nil))
+	// Check if overrideMaps exist when uds sockets are enabled (only pathmaps
+	// will actually have been saved).
+	if opts.privateunixsocket != (s.overrides != nil) {
+		panic(fmt.Sprintf("new privateunixsocket option %v, want %v", opts.privateunixsocket, s.overrides != nil))
 	}
 	if args.Flags != s.superBlockFlags {
 		panic(fmt.Sprintf("new mount flags %v, want %v", args.Flags, s.superBlockFlags))
diff --git a/pkg/sentry/fs/gofer/socket.go b/pkg/sentry/fs/gofer/socket.go
index 376cfce2c..10ba2f5f0 100644
--- a/pkg/sentry/fs/gofer/socket.go
+++ b/pkg/sentry/fs/gofer/socket.go
@@ -32,15 +32,15 @@ func (i *inodeOperations) BoundEndpoint(inode *fs.Inode, path string) transport.
 		return nil
 	}
 
-	if i.session().endpoints != nil {
-		unlock := i.session().endpoints.lock()
+	if i.session().overrides != nil {
+		unlock := i.session().overrides.lock()
 		defer unlock()
-		ep := i.session().endpoints.get(i.fileState.key)
+		ep := i.session().overrides.getBoundEndpoint(i.fileState.key)
 		if ep != nil {
 			return ep
 		}
 
-		// Not found in endpoints map, it may be a gofer backed unix socket...
+		// Not found in overrides map, it may be a gofer backed unix socket...
 	}
 
 	inode.IncRef()