Implement FUSE_UNLINK

Fixes #3696

4 files changed, 82 insertions, 1 deletions

diff --git a/pkg/abi/linux/fuse.go b/pkg/abi/linux/fuse.go
index ca304af05..fdd22a13d 100644
--- a/pkg/abi/linux/fuse.go
+++ b/pkg/abi/linux/fuse.go
@@ -846,3 +846,26 @@ type FUSESetAttrIn struct {
 
 	_ uint32
 }
+
+// FUSEUnlinkIn is the request sent by the kernel to the daemon
+// when trying to unlink a node.
+//
+// Dynamically-sized objects cannot be marshalled.
+type FUSEUnlinkIn struct {
+	marshal.StubMarshallable
+
+	// Name of the node to unlink.
+	Name string
+}
+
+// MarshalBytes serializes r.name to the dst buffer, which should
+// have size len(r.Name) + 1 and last byte set to 0.
+func (r *FUSEUnlinkIn) MarshalBytes(buf []byte) {
+	copy(buf, r.Name)
+}
+
+// SizeBytes is the size of the memory representation of FUSEUnlinkIn.
+// 1 extra byte for null-terminated Name string.
+func (r *FUSEUnlinkIn) SizeBytes() int {
+	return len(r.Name) + 1
+}
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index f4ed73c12..8e749bdad 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -455,6 +455,29 @@ func (i *inode) NewSymlink(ctx context.Context, name, target string) (*vfs.Dentr
 	return i.newEntry(ctx, name, linux.S_IFLNK, linux.FUSE_SYMLINK, &in)
 }
 
+// Unlink implements kernfs.Inode.Unlink.
+func (i *inode) Unlink(ctx context.Context, name string, child *vfs.Dentry) error {
+	kernelTask := kernel.TaskFromContext(ctx)
+	if kernelTask == nil {
+		log.Warningf("fusefs.Inode.newEntry: couldn't get kernel task from context", i.NodeID)
+		return syserror.EINVAL
+	}
+	in := linux.FUSEUnlinkIn{Name: name}
+	req, err := i.fs.conn.NewRequest(auth.CredentialsFromContext(ctx), uint32(kernelTask.ThreadID()), i.NodeID, linux.FUSE_UNLINK, &in)
+	if err != nil {
+		return err
+	}
+	res, err := i.fs.conn.Call(kernelTask, req)
+	if err != nil {
+		return err
+	}
+	// only return error, discard res.
+	if err := res.Error(); err != nil {
+		return err
+	}
+	return i.dentry.RemoveChildLocked(name, child)
+}
+
 // NewDir implements kernfs.Inode.NewDir.
 func (i *inode) NewDir(ctx context.Context, name string, opts vfs.MkdirOptions) (*vfs.Dentry, error) {
 	in := linux.FUSEMkdirIn{
diff --git a/pkg/sentry/fsimpl/kernfs/filesystem.go b/pkg/sentry/fsimpl/kernfs/filesystem.go
index 2823c3b1a..49f6a0f1d 100644
--- a/pkg/sentry/fsimpl/kernfs/filesystem.go
+++ b/pkg/sentry/fsimpl/kernfs/filesystem.go
@@ -770,6 +770,10 @@ func (fs *Filesystem) SymlinkAt(ctx context.Context, rp *vfs.ResolvingPath, targ
 func (fs *Filesystem) UnlinkAt(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, _, err := fs.walkExistingLocked(ctx, rp)
 	fs.processDeferredDecRefsLocked(ctx)
 	if err != nil {
@@ -795,7 +799,7 @@ func (fs *Filesystem) UnlinkAt(ctx context.Context, rp *vfs.ResolvingPath) error
 	if err := virtfs.PrepareDeleteDentry(mntns, vfsd); err != nil {
 		return err
 	}
-	if err := parentDentry.inode.Unlink(ctx, rp.Component(), vfsd); err != nil {
+	if err := parentDentry.inode.Unlink(ctx, name, vfsd); err != nil {
 		virtfs.AbortDeleteDentry(vfsd)
 		return err
 	}
diff --git a/pkg/sentry/fsimpl/kernfs/kernfs.go b/pkg/sentry/fsimpl/kernfs/kernfs.go
index 61189af25..163f26ceb 100644
--- a/pkg/sentry/fsimpl/kernfs/kernfs.go
+++ b/pkg/sentry/fsimpl/kernfs/kernfs.go
@@ -60,6 +60,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
 )
 
 // Filesystem mostly implements vfs.FilesystemImpl for a generic in-memory
@@ -267,6 +268,36 @@ func (d *Dentry) InsertChildLocked(name string, child *Dentry) {
 	d.children[name] = child
 }
 
+// RemoveChild removes child from the vfs dentry cache. This does not update the
+// directory inode or modify the inode to be unlinked. So calling this on its own
+// isn't sufficient to remove a child from a directory.
+//
+// Precondition: d must represent a directory inode.
+func (d *Dentry) RemoveChild(name string, child *vfs.Dentry) error {
+	d.dirMu.Lock()
+	defer d.dirMu.Unlock()
+	return d.RemoveChildLocked(name, child)
+}
+
+// RemoveChildLocked is equivalent to RemoveChild, with additional
+// preconditions.
+//
+// Precondition: d.dirMu must be locked.
+func (d *Dentry) RemoveChildLocked(name string, child *vfs.Dentry) error {
+	if !d.isDir() {
+		panic(fmt.Sprintf("RemoveChild called on non-directory Dentry: %+v.", d))
+	}
+	c, ok := d.children[name]
+	if !ok {
+		return syserror.ENOENT
+	}
+	if &c.vfsd != child {
+		panic(fmt.Sprintf("Dentry hashed into inode doesn't match what vfs thinks! Child: %+v, vfs: %+v", c, child))
+	}
+	delete(d.children, name)
+	return nil
+}
+
 // Inode returns the dentry's inode.
 func (d *Dentry) Inode() Inode {
 	return d.inode