Plumb VFS2 inside the Sentry

- Added fsbridge package with interface that can be used to open
  and read from VFS1 and VFS2 files.
- Converted ELF loader to use fsbridge
- Added VFS2 types to FSContext
- Added vfs.MountNamespace to ThreadGroup

Updates #1623

PiperOrigin-RevId: 295183950

1 files changed, 8 insertions, 2 deletions

diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index ee98eb66a..292f58afd 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -544,6 +544,7 @@ func (fs *Filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 	}
 
 	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
 	virtfs := rp.VirtualFilesystem()
 
 	srcDirDentry := srcDirVFSD.Impl().(*Dentry)
@@ -595,7 +596,10 @@ func (fs *Filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	parentDentry := vfsd.Parent().Impl().(*Dentry)
 	parentDentry.dirMu.Lock()
 	defer parentDentry.dirMu.Unlock()
-	if err := virtfs.PrepareDeleteDentry(vfs.MountNamespaceFromContext(ctx), vfsd); err != nil {
+
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
 		return err
 	}
 	if err := parentDentry.inode.RmDir(ctx, rp.Component(), vfsd); err != nil {
@@ -697,7 +701,9 @@ func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	parentDentry := vfsd.Parent().Impl().(*Dentry)
 	parentDentry.dirMu.Lock()
 	defer parentDentry.dirMu.Unlock()
-	if err := virtfs.PrepareDeleteDentry(vfs.MountNamespaceFromContext(ctx), vfsd); err != nil {
+	mntns := vfs.MountNamespaceFromContext(ctx)
+	defer mntns.DecRef()
+	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
 		return err
 	}
 	if err := parentDentry.inode.Unlink(ctx, rp.Component(), vfsd); err != nil {