runsc/debug: add an option to mount a specified filesystem

A new option, --mount fstype:source:destination, is added to the
debug command which allows us to mount filesystems for debug purposes.
Currently only EROFS is supported.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>

runsc/boot/controller.go

@@ -18,14 +18,19 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"path"
 	gtime "time"
 
 	specs "github.com/opencontainers/runtime-spec/specs-go"
 	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/cleanup"
+	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/control/server"
 	"gvisor.dev/gvisor/pkg/fd"
+	"gvisor.dev/gvisor/pkg/fspath"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/sentry/control"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/erofs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/seccheck"
 	"gvisor.dev/gvisor/pkg/sentry/socket/netstack"
@@ -95,6 +100,9 @@ const (
 
 	// ContMgrProcfsDump dumps sandbox procfs state.
 	ContMgrProcfsDump = "containerManager.ProcfsDump"
+
+	// ContMgrMount mounts a filesystem in a container.
+	ContMgrMount = "containerManager.Mount"
 )
 
 const (
@@ -673,3 +681,95 @@ func (cm *containerManager) ProcfsDump(_ *struct{}, out *[]procfs.ProcessProcfsD
 	}
 	return nil
 }
+
+// MountArgs contains arguments to the Mount method.
+type MountArgs struct {
+	// ContainerID is the container in which we will mount the filesystem.
+	ContainerID string
+
+	// Source is the mount source.
+	Source string
+
+	// Destination is the mount target.
+	Destination string
+
+	// FsType is the filesystem type.
+	FsType string
+
+	// FilePayload contains the source image FD, if required by the filesystem.
+	urpc.FilePayload
+}
+
+const initTID kernel.ThreadID = 1
+
+// Mount mounts a filesystem in a container.
+func (cm *containerManager) Mount(args *MountArgs, _ *struct{}) error {
+	log.Debugf("containerManager.Mount, cid: %s, args: %+v", args.ContainerID, args)
+
+	var cu cleanup.Cleanup
+	defer cu.Clean()
+
+	eid := execID{cid: args.ContainerID}
+	ep, ok := cm.l.processes[eid]
+	if !ok {
+		return fmt.Errorf("container %v is deleted", args.ContainerID)
+	}
+	if ep.tg == nil {
+		return fmt.Errorf("container %v isn't started", args.ContainerID)
+	}
+
+	t := ep.tg.PIDNamespace().TaskWithID(initTID)
+	if t == nil {
+		return fmt.Errorf("failed to find init process")
+	}
+
+	source := args.Source
+	dest := path.Clean(args.Destination)
+	fstype := args.FsType
+
+	if dest[0] != '/' {
+		return fmt.Errorf("absolute path must be provided for destination")
+	}
+
+	var opts vfs.MountOptions
+	switch fstype {
+	case erofs.Name:
+		if len(args.FilePayload.Files) != 1 {
+			return fmt.Errorf("exactly one image file must be provided")
+		}
+
+		imageFD, err := unix.Dup(int(args.FilePayload.Files[0].Fd()))
+		if err != nil {
+			return fmt.Errorf("failed to dup image FD: %v", err)
+		}
+		cu.Add(func() { unix.Close(imageFD) })
+
+		opts = vfs.MountOptions{
+			ReadOnly: true,
+			GetFilesystemOptions: vfs.GetFilesystemOptions{
+				Data: fmt.Sprintf("ifd=%d", imageFD),
+			},
+			InternalMount: true,
+		}
+
+	default:
+		return fmt.Errorf("unsupported filesystem type: %v", fstype)
+	}
+
+	ctx := context.Background()
+	root := t.FSContext().RootDirectory()
+	defer root.DecRef(ctx)
+
+	pop := vfs.PathOperation{
+		Root:  root,
+		Start: root,
+		Path:  fspath.Parse(dest),
+	}
+
+	if _, err := t.Kernel().VFS().MountAt(ctx, t.Credentials(), source, &pop, fstype, &opts); err != nil {
+		return err
+	}
+	log.Infof("Mounted %q to %q type: %s, internal-options: %q, in container %q", source, dest, fstype, opts.GetFilesystemOptions.Data, args.ContainerID)
+	cu.Release()
+	return nil
+}

runsc/cmd/debug.go

@@ -49,6 +49,7 @@ type Debug struct {
 	delay        time.Duration
 	duration     time.Duration
 	ps           bool
+	mount        string
 }
 
 // Name implements subcommands.Command.
@@ -82,6 +83,7 @@ func (d *Debug) SetFlags(f *flag.FlagSet) {
 	f.StringVar(&d.logLevel, "log-level", "", "The log level to set: warning (0), info (1), or debug (2).")
 	f.StringVar(&d.logPackets, "log-packets", "", "A boolean value to enable or disable packet logging: true or false.")
 	f.BoolVar(&d.ps, "ps", false, "lists processes")
+	f.StringVar(&d.mount, "mount", "", "Mount a filesystem (-mount fstype:source:destination).")
 }
 
 // Execute implements subcommands.Command.Execute.
@@ -224,6 +226,18 @@ func (d *Debug) Execute(_ context.Context, f *flag.FlagSet, args ...any) subcomm
 		}
 		util.Infof("%s", o)
 	}
+	if d.mount != "" {
+		opts := strings.Split(d.mount, ":")
+		if len(opts) != 3 {
+			util.Fatalf("Mount failed: invalid option: %v", d.mount)
+		}
+		fstype := opts[0]
+		src := opts[1]
+		dest := opts[2]
+		if err := c.Sandbox.Mount(c.ID, fstype, src, dest); err != nil {
+			util.Fatalf(err.Error())
+		}
+	}
 
 	// Open profiling files.
 	var (

runsc/sandbox/BUILD

@@ -28,6 +28,7 @@ go_library(
         "//pkg/metric:metric_go_proto",
         "//pkg/prometheus",
         "//pkg/sentry/control",
+        "//pkg/sentry/fsimpl/erofs",
         "//pkg/sentry/platform",
         "//pkg/sentry/seccheck",
         "//pkg/state/statefile",

runsc/sandbox/sandbox.go

@@ -44,6 +44,7 @@ import (
 	metricpb "gvisor.dev/gvisor/pkg/metric/metric_go_proto"
 	"gvisor.dev/gvisor/pkg/prometheus"
 	"gvisor.dev/gvisor/pkg/sentry/control"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/erofs"
 	"gvisor.dev/gvisor/pkg/sentry/platform"
 	"gvisor.dev/gvisor/pkg/sentry/seccheck"
 	"gvisor.dev/gvisor/pkg/state/statefile"
@@ -1669,3 +1670,28 @@ func SetUserMappings(spec *specs.Spec, pid int) error {
 	}
 	return nil
 }
+
+// Mount mounts a filesystem in a container.
+func (s *Sandbox) Mount(cid, fstype, src, dest string) error {
+	var files []*os.File
+	switch fstype {
+	case erofs.Name:
+		if imageFile, err := os.Open(src); err != nil {
+			return fmt.Errorf("opening %s: %v", src, err)
+		} else {
+			files = append(files, imageFile)
+		}
+
+	default:
+		return fmt.Errorf("unsupported filesystem type: %v", fstype)
+	}
+
+	args := boot.MountArgs{
+		ContainerID: cid,
+		Source:      src,
+		Destination: dest,
+		FsType:      fstype,
+		FilePayload: urpc.FilePayload{Files: files},
+	}
+	return s.call(boot.ContMgrMount, &args, nil)
+}