From 6c26cda53122df871befd0c1e08b892e0d56d31e Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher <jakobunt@gmail.com>
Date: Sat, 1 Aug 2020 22:28:25 +0200
Subject: [PATCH] v2api/reverse: implement Readdir

---
 internal/fusefrontend_reverse/node_dir_ops.go | 81 +++++++++++++++++++
 internal/fusefrontend_reverse/node_helpers.go |  6 ++
 internal/fusefrontend_reverse/virtualfile.go  | 15 ++++
 3 files changed, 102 insertions(+)
 create mode 100644 internal/fusefrontend_reverse/node_dir_ops.go
 create mode 100644 internal/fusefrontend_reverse/virtualfile.go

diff --git a/internal/fusefrontend_reverse/node_dir_ops.go b/internal/fusefrontend_reverse/node_dir_ops.go
new file mode 100644
index 0000000..c48d884
--- /dev/null
+++ b/internal/fusefrontend_reverse/node_dir_ops.go
@@ -0,0 +1,81 @@
+package fusefrontend_reverse
+
+import (
+	"context"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+
+	"github.com/hanwen/go-fuse/v2/fs"
+	"github.com/hanwen/go-fuse/v2/fuse"
+
+	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/nametransform"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+)
+
+// Readdir - FUSE call.
+//
+// This function is symlink-safe through use of openBackingDir() and
+// ReadDirIVAt().
+func (n *Node) Readdir(ctx context.Context) (stream fs.DirStream, errno syscall.Errno) {
+	dirfd, cName, errno := n.prepareAtSyscall("")
+	if errno != 0 {
+		return
+	}
+	defer syscall.Close(dirfd)
+
+	// Read plaintext directory
+	var entries []fuse.DirEntry
+	fd, err := syscallcompat.Openat(dirfd, cName, syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		return nil, fs.ToErrno(err)
+	}
+	defer syscall.Close(fd)
+	entries, err = syscallcompat.Getdents(fd)
+	if err != nil {
+		return nil, fs.ToErrno(err)
+	}
+
+	rn := n.rootNode()
+	if rn.args.PlaintextNames {
+		panic("todo")
+	}
+
+	// Filter out excluded entries
+	//TODO
+	//entries = rfs.excludeDirEntries(relPath, entries)
+
+	// Virtual files: at least one gocryptfs.diriv file
+	virtualFiles := []fuse.DirEntry{
+		{Mode: virtualFileMode, Name: nametransform.DirIVFilename},
+	}
+
+	cipherPath := n.Path()
+	dirIV := pathiv.Derive(cipherPath, pathiv.PurposeDirIV)
+	// Encrypt names
+	for i := range entries {
+		var cName string
+		// ".gocryptfs.reverse.conf" in the root directory is mapped to "gocryptfs.conf"
+		if n.isRoot() && entries[i].Name == configfile.ConfReverseName &&
+			!rn.args.ConfigCustom {
+			cName = configfile.ConfDefaultName
+		} else {
+			cName = rn.nameTransform.EncryptName(entries[i].Name, dirIV)
+			if len(cName) > unix.NAME_MAX {
+				cName = rn.nameTransform.HashLongName(cName)
+				dotNameFile := fuse.DirEntry{
+					Mode: virtualFileMode,
+					Name: cName + nametransform.LongNameSuffix,
+				}
+				virtualFiles = append(virtualFiles, dotNameFile)
+			}
+		}
+		entries[i].Name = cName
+	}
+
+	// Add virtual files
+	entries = append(entries, virtualFiles...)
+	return fs.NewListDirStream(entries), 0
+}
diff --git a/internal/fusefrontend_reverse/node_helpers.go b/internal/fusefrontend_reverse/node_helpers.go
index a26ee81..24cdbd1 100644
--- a/internal/fusefrontend_reverse/node_helpers.go
+++ b/internal/fusefrontend_reverse/node_helpers.go
@@ -65,3 +65,9 @@ func (n *Node) newChild(ctx context.Context, st *syscall.Stat_t, out *fuse.Entry
 	node := &Node{}
 	return n.NewInode(ctx, node, id)
 }
+
+// isRoot returns true if this node is the root node
+func (n *Node) isRoot() bool {
+	rn := n.rootNode()
+	return &rn.Node == n
+}
diff --git a/internal/fusefrontend_reverse/virtualfile.go b/internal/fusefrontend_reverse/virtualfile.go
new file mode 100644
index 0000000..a92c127
--- /dev/null
+++ b/internal/fusefrontend_reverse/virtualfile.go
@@ -0,0 +1,15 @@
+package fusefrontend_reverse
+
+import (
+	"syscall"
+)
+
+const (
+	// virtualFileMode is the mode to use for virtual files (gocryptfs.diriv and
+	// *.name). They are always readable, as stated in func Access
+	virtualFileMode = syscall.S_IFREG | 0444
+	// We use inomap's `Tag` feature to generate unique inode numbers for
+	// virtual files. These are the tags we use.
+	inoTagDirIV    = 1
+	inoTagNameFile = 2
+)