Make mounts ReadWrite first, then later change to ReadOnly.

This lets us create "synthetic" mountpoint directories in ReadOnly mounts
during VFS setup.

Also add context.WithMountNamespace, as some filesystems (like overlay) require
a MountNamespace on ctx to handle vfs.Filesystem Operations.

PiperOrigin-RevId: 327874971

1 files changed, 38 insertions, 17 deletions

diff --git a/runsc/boot/vfs.go b/runsc/boot/vfs.go
index f27a6ff6b..fb200e988 100644
--- a/runsc/boot/vfs.go
+++ b/runsc/boot/vfs.go
@@ -205,15 +205,34 @@ func (c *containerMounter) mountSubmountsVFS2(ctx context.Context, conf *config.
 	for i := range mounts {
 		submount := &mounts[i]
 		log.Debugf("Mounting %q to %q, type: %s, options: %s", submount.Source, submount.Destination, submount.Type, submount.Options)
+		var (
+			mnt *vfs.Mount
+			err error
+		)
+
 		if hint := c.hints.findMount(submount.Mount); hint != nil && hint.isSupported() {
-			if err := c.mountSharedSubmountVFS2(ctx, conf, mns, creds, submount.Mount, hint); err != nil {
+			mnt, err = c.mountSharedSubmountVFS2(ctx, conf, mns, creds, submount.Mount, hint)
+			if err != nil {
 				return fmt.Errorf("mount shared mount %q to %q: %v", hint.name, submount.Destination, err)
 			}
 		} else {
-			if err := c.mountSubmountVFS2(ctx, conf, mns, creds, submount); err != nil {
+			mnt, err = c.mountSubmountVFS2(ctx, conf, mns, creds, submount)
+			if err != nil {
 				return fmt.Errorf("mount submount %q: %w", submount.Destination, err)
 			}
 		}
+
+		if mnt != nil && mnt.ReadOnly() {
+			// Switch to ReadWrite while we setup submounts.
+			if err := c.k.VFS().SetMountReadOnly(mnt, false); err != nil {
+				return fmt.Errorf("failed to set mount at %q readwrite: %v", submount.Destination, err)
+			}
+			defer func() {
+				if err := c.k.VFS().SetMountReadOnly(mnt, true); err != nil {
+					panic(fmt.Sprintf("failed to restore mount at %q back to readonly: %v", submount.Destination, err))
+				}
+			}()
+		}
 	}
 
 	if err := c.mountTmpVFS2(ctx, conf, creds, mns); err != nil {
@@ -256,7 +275,7 @@ func (c *containerMounter) prepareMountsVFS2() ([]mountAndFD, error) {
 	return mounts, nil
 }
 
-func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.Config, mns *vfs.MountNamespace, creds *auth.Credentials, submount *mountAndFD) error {
+func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.Config, mns *vfs.MountNamespace, creds *auth.Credentials, submount *mountAndFD) (*vfs.Mount, error) {
 	root := mns.Root()
 	defer root.DecRef(ctx)
 	target := &vfs.PathOperation{
@@ -266,21 +285,22 @@ func (c *containerMounter) mountSubmountVFS2(ctx context.Context, conf *config.C
 	}
 	fsName, opts, err := c.getMountNameAndOptionsVFS2(conf, submount)
 	if err != nil {
-		return fmt.Errorf("mountOptions failed: %w", err)
+		return nil, fmt.Errorf("mountOptions failed: %w", err)
 	}
 	if len(fsName) == 0 {
 		// Filesystem is not supported (e.g. cgroup), just skip it.
-		return nil
+		return nil, nil
 	}
 
 	if err := c.k.VFS().MkdirAllAt(ctx, submount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
-		return err
+		return nil, err
 	}
-	if err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts); err != nil {
-		return fmt.Errorf("failed to mount %q (type: %s): %w, opts: %v", submount.Destination, submount.Type, err, opts)
+	mnt, err := c.k.VFS().MountAt(ctx, creds, "", target, fsName, opts)
+	if err != nil {
+		return nil, fmt.Errorf("failed to mount %q (type: %s): %w, opts: %v", submount.Destination, submount.Type, err, opts)
 	}
 	log.Infof("Mounted %q to %q type: %s, internal-options: %q", submount.Source, submount.Destination, submount.Type, opts.GetFilesystemOptions.Data)
-	return nil
+	return mnt, nil
 }
 
 // getMountNameAndOptionsVFS2 retrieves the fsName, opts, and useOverlay values
@@ -407,7 +427,8 @@ func (c *containerMounter) mountTmpVFS2(ctx context.Context, conf *config.Config
 			// another user. This is normally done for /tmp.
 			Options: []string{"mode=01777"},
 		}
-		return c.mountSubmountVFS2(ctx, conf, mns, creds, &mountAndFD{Mount: tmpMount})
+		_, err := c.mountSubmountVFS2(ctx, conf, mns, creds, &mountAndFD{Mount: tmpMount})
+		return err
 
 	case syserror.ENOTDIR:
 		// Not a dir?! Let it be.
@@ -458,25 +479,25 @@ func (c *containerMounter) mountSharedMasterVFS2(ctx context.Context, conf *conf
 
 // mountSharedSubmount binds mount to a previously mounted volume that is shared
 // among containers in the same pod.
-func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *config.Config, mns *vfs.MountNamespace, creds *auth.Credentials, mount specs.Mount, source *mountHint) error {
+func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *config.Config, mns *vfs.MountNamespace, creds *auth.Credentials, mount specs.Mount, source *mountHint) (*vfs.Mount, error) {
 	if err := source.checkCompatible(mount); err != nil {
-		return err
+		return nil, err
 	}
 
 	_, opts, err := c.getMountNameAndOptionsVFS2(conf, &mountAndFD{Mount: mount})
 	if err != nil {
-		return err
+		return nil, err
 	}
 	newMnt, err := c.k.VFS().NewDisconnectedMount(source.vfsMount.Filesystem(), source.vfsMount.Root(), opts)
 	if err != nil {
-		return err
+		return nil, err
 	}
 	defer newMnt.DecRef(ctx)
 
 	root := mns.Root()
 	defer root.DecRef(ctx)
 	if err := c.k.VFS().MkdirAllAt(ctx, mount.Destination, root, creds, &vfs.MkdirOptions{Mode: 0777, ForSyntheticMountpoint: true}); err != nil {
-		return err
+		return nil, err
 	}
 
 	target := &vfs.PathOperation{
@@ -485,8 +506,8 @@ func (c *containerMounter) mountSharedSubmountVFS2(ctx context.Context, conf *co
 		Path:  fspath.Parse(mount.Destination),
 	}
 	if err := c.k.VFS().ConnectMountAt(ctx, creds, newMnt, target); err != nil {
-		return err
+		return nil, err
 	}
 	log.Infof("Mounted %q type shared bind to %q", mount.Destination, source.name)
-	return nil
+	return newMnt, nil
 }