3 files changed, 50 insertions, 34 deletions
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index 7847e3cc2..a26b13067 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -42,7 +42,7 @@ type filesystemType struct{}
 
 // GetFilesystem implements FilesystemType.GetFilesystem.
 func (filesystemType) GetFilesystem(context.Context, *vfs.VirtualFilesystem, *auth.Credentials, string, vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
-	panic("cannot instaniate a host filesystem")
+	panic("host.filesystemType.GetFilesystem should never be called")
 }
 
 // Name implements FilesystemType.Name.
@@ -55,14 +55,14 @@ type filesystem struct {
 	kernfs.Filesystem
 }
 
-// NewMount returns a new disconnected mount in vfsObj that may be passed to ImportFD.
-func NewMount(vfsObj *vfs.VirtualFilesystem) (*vfs.Mount, error) {
+// NewFilesystem sets up and returns a new hostfs filesystem.
+//
+// Note that there should only ever be one instance of host.filesystem,
+// a global mount for host fds.
+func NewFilesystem(vfsObj *vfs.VirtualFilesystem) *vfs.Filesystem {
 	fs := &filesystem{}
-	fs.Init(vfsObj, &filesystemType{})
-	vfsfs := fs.VFSFilesystem()
-	// NewDisconnectedMount will take an additional reference on vfsfs.
-	defer vfsfs.DecRef()
-	return vfsObj.NewDisconnectedMount(vfsfs, nil, &vfs.MountOptions{})
+	fs.Init(vfsObj, filesystemType{})
+	return fs.VFSFilesystem()
 }
 
 // ImportFD sets up and returns a vfs.FileDescription from a donated fd.
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
index 3f7ad1d65..632cfde88 100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -24,26 +24,12 @@ import (
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
-// NewFilesystem creates a new sockfs filesystem.
-//
-// Note that there should only ever be one instance of sockfs.Filesystem,
-// backing a global socket mount.
-func NewFilesystem(vfsObj *vfs.VirtualFilesystem) *vfs.Filesystem {
-	fs, _, err := filesystemType{}.GetFilesystem(nil, vfsObj, nil, "", vfs.GetFilesystemOptions{})
-	if err != nil {
-		panic("failed to create sockfs filesystem")
-	}
-	return fs
-}
-
 // filesystemType implements vfs.FilesystemType.
 type filesystemType struct{}
 
 // GetFilesystem implements FilesystemType.GetFilesystem.
 func (fsType filesystemType) GetFilesystem(_ context.Context, vfsObj *vfs.VirtualFilesystem, _ *auth.Credentials, _ string, _ vfs.GetFilesystemOptions) (*vfs.Filesystem, *vfs.Dentry, error) {
-	fs := &filesystem{}
-	fs.Init(vfsObj, fsType)
-	return fs.VFSFilesystem(), nil, nil
+	panic("sockfs.filesystemType.GetFilesystem should never be called")
 }
 
 // Name implements FilesystemType.Name.
@@ -60,6 +46,16 @@ type filesystem struct {
 	kernfs.Filesystem
 }
 
+// NewFilesystem sets up and returns a new sockfs filesystem.
+//
+// Note that there should only ever be one instance of sockfs.Filesystem,
+// backing a global socket mount.
+func NewFilesystem(vfsObj *vfs.VirtualFilesystem) *vfs.Filesystem {
+	fs := &filesystem{}
+	fs.Init(vfsObj, filesystemType{})
+	return fs.VFSFilesystem()
+}
+
 // inode implements kernfs.Inode.
 //
 // TODO(gvisor.dev/issue/1476): Add device numbers to this inode (which are
diff --git a/pkg/sentry/kernel/kernel.go b/pkg/sentry/kernel/kernel.go
index fef60e636..c91b9dce2 100644
--- a/pkg/sentry/kernel/kernel.go
+++ b/pkg/sentry/kernel/kernel.go
@@ -227,11 +227,6 @@ type Kernel struct {
 	// by extMu.
 	nextSocketEntry uint64
 
-	// socketMount is a disconnected vfs.Mount, not included in k.vfs,
-	// representing a sockfs.filesystem. socketMount is used to back
-	// VirtualDentries representing anonymous sockets.
-	socketMount *vfs.Mount
-
 	// deviceRegistry is used to save/restore device.SimpleDevices.
 	deviceRegistry struct{} `state:".(*device.Registry)"`
 
@@ -255,10 +250,22 @@ type Kernel struct {
 	// VFS keeps the filesystem state used across the kernel.
 	vfs vfs.VirtualFilesystem
 
+	// hostMount is the Mount used for file descriptors that were imported
+	// from the host.
+	hostMount *vfs.Mount
+
 	// pipeMount is the Mount used for pipes created by the pipe() and pipe2()
 	// syscalls (as opposed to named pipes created by mknod()).
 	pipeMount *vfs.Mount
 
+	// socketMount is the Mount used for sockets created by the socket() and
+	// socketpair() syscalls. There are several cases where a socket dentry will
+	// not be contained in socketMount:
+	// 1. Socket files created by mknod()
+	// 2. Socket fds imported from the host (Kernel.hostMount is used for these)
+	// 3. Socket files created by binding Unix sockets to a file path
+	socketMount *vfs.Mount
+
 	// If set to true, report address space activation waits as if the task is in
 	// external wait so that the watchdog doesn't report the task stuck.
 	SleepForAddressSpaceActivation bool
@@ -377,7 +384,7 @@ func (k *Kernel) Init(args InitKernelArgs) error {
 		defer socketFilesystem.DecRef()
 		socketMount, err := k.vfs.NewDisconnectedMount(socketFilesystem, nil, &vfs.MountOptions{})
 		if err != nil {
-			return fmt.Errorf("failed to initialize socket mount: %v", err)
+			return fmt.Errorf("failed to create sockfs mount: %v", err)
 		}
 		k.socketMount = socketMount
 	}
@@ -1526,11 +1533,6 @@ func (k *Kernel) ListSockets() []*SocketEntry {
 	return socks
 }
 
-// SocketMount returns the global socket mount.
-func (k *Kernel) SocketMount() *vfs.Mount {
-	return k.socketMount
-}
-
 // supervisorContext is a privileged context.
 type supervisorContext struct {
 	context.NoopSleeper
@@ -1629,7 +1631,25 @@ func (k *Kernel) VFS() *vfs.VirtualFilesystem {
 	return &k.vfs
 }
 
+// SetHostMount sets the hostfs mount.
+func (k *Kernel) SetHostMount(mnt *vfs.Mount) {
+	if k.hostMount != nil {
+		panic("Kernel.hostMount cannot be set more than once")
+	}
+	k.hostMount = mnt
+}
+
+// HostMount returns the hostfs mount.
+func (k *Kernel) HostMount() *vfs.Mount {
+	return k.hostMount
+}
+
 // PipeMount returns the pipefs mount.
 func (k *Kernel) PipeMount() *vfs.Mount {
 	return k.pipeMount
 }
+
+// SocketMount returns the sockfs mount.
+func (k *Kernel) SocketMount() *vfs.Mount {
+	return k.socketMount
+}