[vfs] Create recursive dir creation util.

Refactored the recursive dir creation util in runsc/boot/vfs.go to be more
flexible.

PiperOrigin-RevId: 327719100

pkg/sentry/vfs/vfs.go

@@ -36,6 +36,7 @@ package vfs
 
 import (
 	"fmt"
+	"path"
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
@@ -782,6 +783,38 @@ func (vfs *VirtualFilesystem) SyncAllFilesystems(ctx context.Context) error {
 	return retErr
 }
 
+// MkdirAllAt recursively creates non-existent directories on the given path
+// (including the last component).
+func (vfs *VirtualFilesystem) MkdirAllAt(ctx context.Context, currentPath string, root VirtualDentry, creds *auth.Credentials, mkdirOpts *MkdirOptions) error {
+	pop := &PathOperation{
+		Root:  root,
+		Start: root,
+		Path:  fspath.Parse(currentPath),
+	}
+	stat, err := vfs.StatAt(ctx, creds, pop, &StatOptions{Mask: linux.STATX_TYPE})
+	switch err {
+	case nil:
+		if stat.Mask&linux.STATX_TYPE == 0 || stat.Mode&linux.FileTypeMask != linux.ModeDirectory {
+			return syserror.ENOTDIR
+		}
+		// Directory already exists.
+		return nil
+	case syserror.ENOENT:
+		// Expected, we will create the dir.
+	default:
+		return fmt.Errorf("stat failed for %q during directory creation: %w", currentPath, err)
+	}
+
+	// Recurse to ensure parent is created and then create the final directory.
+	if err := vfs.MkdirAllAt(ctx, path.Dir(currentPath), root, creds, mkdirOpts); err != nil {
+		return err
+	}
+	if err := vfs.MkdirAt(ctx, creds, pop, mkdirOpts); err != nil {
+		return fmt.Errorf("failed to create directory %q: %w", currentPath, err)
+	}
+	return nil
+}
+
 // A VirtualDentry represents a node in a VFS tree, by combining a Dentry
 // (which represents a node in a Filesystem's tree) and a Mount (which
 // represents the Filesystem's position in a VFS mount tree).

runsc/boot/vfs.go

@@ -16,7 +16,6 @@ package boot
 
 import (
 	"fmt"
-	"path"
 	"sort"
 	"strings"
 
@@ -274,7 +273,7 @@ func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.C
 		return nil
 	}
 
-	if err := c.makeSyntheticMount(ctx, submount.Destination, root, creds); err != nil {
+	if err := c.k.VFS().MkdirAllAt(ctx, submount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
 		return err
 	}
 	if err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts); err != nil {
@@ -348,33 +347,6 @@ func (c *containerMounter) getMountNameAndOptionsVFS2(conf *config.Config, m *mo
 	return fsName, opts, nil
 }
 
-func (c *containerMounter) makeSyntheticMount(ctx context.Context, currentPath string, root vfs.VirtualDentry, creds *auth.Credentials) error {
-	target := &vfs.PathOperation{
-		Root:  root,
-		Start: root,
-		Path:  fspath.Parse(currentPath),
-	}
-	_, err := c.k.VFS().StatAt(ctx, creds, target, &vfs.StatOptions{})
-	if err == nil {
-		log.Debugf("Mount point %q already exists", currentPath)
-		return nil
-	}
-	if err != syserror.ENOENT {
-		return fmt.Errorf("stat failed for %q during mount point creation: %w", currentPath, err)
-	}
-
-	// Recurse to ensure parent is created and then create the mount point.
-	if err := c.makeSyntheticMount(ctx, path.Dir(currentPath), root, creds); err != nil {
-		return err
-	}
-	log.Debugf("Creating dir %q for mount point", currentPath)
-	mkdirOpts := &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}
-	if err := c.k.VFS().MkdirAt(ctx, creds, target, mkdirOpts); err != nil {
-		return fmt.Errorf("failed to create directory %q for mount: %w", currentPath, err)
-	}
-	return nil
-}
-
 // mountTmpVFS2 mounts an internal tmpfs at '/tmp' if it's safe to do so.
 // Technically we don't have to mount tmpfs at /tmp, as we could just rely on
 // the host /tmp, but this is a nice optimization, and fixes some apps that call
@@ -503,7 +475,7 @@ func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *co
 
 	root := mns.Root()
 	defer root.DecRef(ctx)
-	if err := c.makeSyntheticMount(ctx, mount.Destination, root, creds); err != nil {
+	if err := c.k.VFS().MkdirAllAt(ctx, mount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
 		return err
 	}