Implement FUSE_RMDIR

Fixes #3587

Co-authored-by: Craig Chi <craigchi@google.com>

3 files changed, 59 insertions, 1 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index 0ece7b756..c75debb8c 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -569,3 +569,29 @@ func (r *FUSEMkdirIn) MarshalUnsafe(buf []byte) {
 func (r *FUSEMkdirIn) SizeBytes() int {
 	return r.MkdirMeta.SizeBytes() + len(r.Name) + 1
 }
+
+// FUSERmDirIn is the request sent by the kernel to the daemon
+// when trying to remove a directory.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSERmDirIn struct {
+	marshal.StubMarshallable
+
+	// Name is a directory name to be looked up.
+	Name string
+}
+
+// MarshalUnsafe serializes r.name to the dst buffer.
+func (r *FUSERmDirIn) MarshalUnsafe(buf []byte) {
+	copy(buf, r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSERmDirIn.
+func (r *FUSERmDirIn) SizeBytes() int {
+	return len(r.Name) + 1
+}
+
+// UnmarshalUnsafe deserializes r.name from the src buffer.
+func (r *FUSERmDirIn) UnmarshalUnsafe(src []byte) {
+	r.Name = string(src)
+}
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index 65e22ba4d..c55ea927a 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -426,6 +426,33 @@ func (i *inode) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions)
 	return i.newEntry(ctx, name, linux.S_IFDIR, linux.FUSE_MKDIR, &in)
 }
 
+// RmDir implements kernfs.Inode.RmDir.
+func (i *inode) RmDir(ctx context.Context, name string, child *vfs.Dentry) error {
+	fusefs := i.fs
+	task, creds := kernel.TaskFromContext(ctx), auth.CredentialsFromContext(ctx)
+
+	in := linux.FUSERmDirIn{Name: name}
+	req, err := fusefs.conn.NewRequest(creds, uint32(task.ThreadID()), i.NodeID, linux.FUSE_RMDIR, &in)
+	if err != nil {
+		return err
+	}
+
+	res, err := i.fs.conn.Call(task, req)
+	if err != nil {
+		return err
+	}
+	if err := res.Error(); err != nil {
+		return err
+	}
+
+	// TODO(Before merging): When creating new nodes, should we add nodes to the ordered children?
+	// If so we'll probably need to call this. We will also need to add them with the writable flag when
+	// appropriate.
+	// return i.OrderedChildren.RmDir(ctx, name, child)
+
+	return nil
+}
+
 // newEntry calls FUSE server for entry creation and allocates corresponding entry according to response.
 // Shared by FUSE_MKNOD, FUSE_MKDIR, FUSE_SYMLINK, FUSE_LINK and FUSE_LOOKUP.
 func (i *inode) newEntry(ctx context.Context, name string, fileType linux.FileMode, opcode linux.FUSEOpcode, payload marshal.Marshallable) (*vfs.Dentry, error) {
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 7aaf1146d..2823c3b1a 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -657,6 +657,10 @@ func (fs *Filesystem) RenameAt(ctx context.Context, rp *vfs.ResolvingPath, oldPa
 func (fs *Filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error {
 	fs.mu.Lock()
 	defer fs.mu.Unlock()
+
+	// Store the name before walkExistingLocked as rp will be advanced past the
+	// name in the following call.
+	name := rp.Component()
 	vfsd, inode, err := fs.walkExistingLocked(ctx, rp)
 	fs.processDeferredDecRefsLocked(ctx)
 	if err != nil {
@@ -686,7 +690,8 @@ func (fs *Filesystem) RmdirAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
 		return err
 	}
-	if err := parentDentry.inode.RmDir(ctx, rp.Component(), vfsd); err != nil {
+
+	if err := parentDentry.inode.RmDir(ctx, name, vfsd); err != nil {
 		virtfs.AbortDeleteDentry(vfsd)
 		return err
 	}