4 files changed, 139 insertions, 2 deletions
diff --git a/internal/fusefrontend/fs_dir.go b/internal/fusefrontend/fs_dir.go
index 8481d56..0d8adae 100644
--- a/internal/fusefrontend/fs_dir.go
+++ b/internal/fusefrontend/fs_dir.go
@@ -30,7 +30,7 @@ func (fs *FS) mkdirWithIv(dirfd int, cName string, mode uint32, context *fuse.Co
 	// from seeing it.
 	fs.dirIVLock.Lock()
 	defer fs.dirIVLock.Unlock()
-	err := syscallcompat.MkdiratUser(dirfd, cName, mode, context)
+	err := syscallcompat.MkdiratUser(dirfd, cName, mode, &context.Caller)
 	if err != nil {
 		return err
 	}
@@ -67,7 +67,7 @@ func (fs *FS) Mkdir(newPath string, mode uint32, context *fuse.Context) (code fu
 		context = nil
 	}
 	if fs.args.PlaintextNames {
-		err = syscallcompat.MkdiratUser(dirfd, cName, mode, context)
+		err = syscallcompat.MkdiratUser(dirfd, cName, mode, &context.Caller)
 		return fuse.ToStatus(err)
 	}
 
diff --git a/internal/fusefrontend/node_api_check.go b/internal/fusefrontend/node_api_check.go
new file mode 100644
index 0000000..e6d1681
--- /dev/null
+++ b/internal/fusefrontend/node_api_check.go
@@ -0,0 +1,11 @@
+package fusefrontend
+
+import (
+	"github.com/hanwen/go-fuse/v2/fs"
+)
+
+var _ = (fs.NodeGetattrer)((*Node)(nil))
+var _ = (fs.NodeLookuper)((*Node)(nil))
+var _ = (fs.NodeReaddirer)((*Node)(nil))
+var _ = (fs.NodeCreater)((*Node)(nil))
+var _ = (fs.NodeMkdirer)((*Node)(nil))
diff --git a/internal/fusefrontend/node_dir_ops.go b/internal/fusefrontend/node_dir_ops.go
index 38d0940..0789c92 100644
--- a/internal/fusefrontend/node_dir_ops.go
+++ b/internal/fusefrontend/node_dir_ops.go
@@ -5,6 +5,8 @@ import (
 	"path/filepath"
 	"syscall"
 
+	"golang.org/x/sys/unix"
+
 	"github.com/hanwen/go-fuse/v2/fs"
 	"github.com/hanwen/go-fuse/v2/fuse"
 
@@ -14,6 +16,125 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
+// mkdirWithIv - create a new directory and corresponding diriv file. dirfd
+// should be a handle to the parent directory, cName is the name of the new
+// directory and mode specifies the access permissions to use.
+func (n *Node) mkdirWithIv(dirfd int, cName string, mode uint32, caller *fuse.Caller) error {
+	rn := n.rootNode()
+	// Between the creation of the directory and the creation of gocryptfs.diriv
+	// the directory is inconsistent. Take the lock to prevent other readers
+	// from seeing it.
+	rn.dirIVLock.Lock()
+	defer rn.dirIVLock.Unlock()
+	err := syscallcompat.MkdiratUser(dirfd, cName, mode, caller)
+	if err != nil {
+		return err
+	}
+	dirfd2, err := syscallcompat.Openat(dirfd, cName, syscall.O_DIRECTORY|syscall.O_NOFOLLOW|syscallcompat.O_PATH, 0)
+	if err == nil {
+		// Create gocryptfs.diriv
+		err = nametransform.WriteDirIVAt(dirfd2)
+		syscall.Close(dirfd2)
+	}
+	if err != nil {
+		// Delete inconsistent directory (missing gocryptfs.diriv!)
+		err2 := syscallcompat.Unlinkat(dirfd, cName, unix.AT_REMOVEDIR)
+		if err2 != nil {
+			tlog.Warn.Printf("mkdirWithIv: rollback failed: %v", err2)
+		}
+	}
+	return err
+}
+
+// Mkdir - FUSE call. Create a directory at "newPath" with permissions "mode".
+//
+// Symlink-safe through use of Mkdirat().
+func (n *Node) Mkdir(ctx context.Context, name string, mode uint32, out *fuse.EntryOut) (*fs.Inode, syscall.Errno) {
+	rn := n.rootNode()
+	newPath := filepath.Join(n.path(), name)
+	if rn.isFiltered(newPath) {
+		return nil, syscall.EPERM
+	}
+	dirfd, cName, err := rn.openBackingDir(newPath)
+	if err != nil {
+		return nil, fs.ToErrno(err)
+	}
+	defer syscall.Close(dirfd)
+	var caller *fuse.Caller
+	if rn.args.PreserveOwner {
+		caller, _ = fuse.FromContext(ctx)
+	}
+	if rn.args.PlaintextNames {
+		err = syscallcompat.MkdiratUser(dirfd, cName, mode, caller)
+		return nil, fs.ToErrno(err)
+	}
+
+	// We need write and execute permissions to create gocryptfs.diriv.
+	// Also, we need read permissions to open the directory (to avoid
+	// race-conditions between getting and setting the mode).
+	origMode := mode
+	mode = mode | 0700
+
+	// Handle long file name
+	if nametransform.IsLongContent(cName) {
+		// Create ".name"
+		err = rn.nameTransform.WriteLongNameAt(dirfd, cName, newPath)
+		if err != nil {
+			return nil, fs.ToErrno(err)
+		}
+
+		// Create directory
+		err = rn.mkdirWithIv(dirfd, cName, mode, caller)
+		if err != nil {
+			nametransform.DeleteLongNameAt(dirfd, cName)
+			return nil, fs.ToErrno(err)
+		}
+	} else {
+		err = rn.mkdirWithIv(dirfd, cName, mode, caller)
+		if err != nil {
+			return nil, fs.ToErrno(err)
+		}
+	}
+
+	fd, err := syscallcompat.Openat(dirfd, cName,
+		syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		tlog.Warn.Printf("Mkdir %q: Openat failed: %v", cName, err)
+		return nil, fs.ToErrno(err)
+	}
+	defer syscall.Close(fd)
+
+	// Get unique inode number
+	var st syscall.Stat_t
+	err = syscall.Fstat(fd, &st)
+	if err != nil {
+		tlog.Warn.Printf("Mkdir %q: Fstat failed: %v", cName, err)
+		return nil, fs.ToErrno(err)
+	}
+	rn.inoMap.TranslateStat(&st)
+	out.Attr.FromStat(&st)
+	// Create child node
+	id := fs.StableAttr{
+		Mode: uint32(st.Mode),
+		Gen:  1,
+		Ino:  st.Ino,
+	}
+	node := &Node{}
+	ch := n.NewInode(ctx, node, id)
+
+	// Set mode
+	if origMode != mode {
+		// Preserve SGID bit if it was set due to inheritance.
+		origMode = uint32(st.Mode&^0777) | origMode
+		err = syscall.Fchmod(fd, origMode)
+		if err != nil {
+			tlog.Warn.Printf("Mkdir %q: Fchmod %#o -> %#o failed: %v", cName, mode, origMode, err)
+		}
+	}
+
+	return ch, 0
+}
+
 func (n *Node) Readdir(ctx context.Context) (fs.DirStream, syscall.Errno) {
 	rn := n.rootNode()
 	p := n.path()
diff --git a/internal/fusefrontend/root_node.go b/internal/fusefrontend/root_node.go
index c84ac93..be82851 100644
--- a/internal/fusefrontend/root_node.go
+++ b/internal/fusefrontend/root_node.go
@@ -2,6 +2,7 @@ package fusefrontend
 
 import (
 	"os"
+	"sync"
 	"sync/atomic"
 	"syscall"
 	"time"
@@ -19,6 +20,10 @@ type RootNode struct {
 	Node
 	// args stores configuration arguments
 	args Args
+	// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
+	// Readers must RLock() it to prevent them from seeing intermediate
+	// states
+	dirIVLock sync.RWMutex
 	// Filename encryption helper
 	nameTransform nametransform.NameTransformer
 	// Content encryption helper