From cc0b94a3c58c942250c0b2728c2d95123b0decf1 Mon Sep 17 00:00:00 2001
From: Jakob Unterwurzacher
Date: Sun, 21 Jun 2020 13:57:04 +0200
Subject: v2api: implement Rmdir

---
 internal/fusefrontend/node_api_check.go |   1 +
 internal/fusefrontend/node_dir_ops.go   | 128 ++++++++++++++++++++++++++++++++
 2 files changed, 129 insertions(+)

diff --git a/internal/fusefrontend/node_api_check.go b/internal/fusefrontend/node_api_check.go
index e6d1681..8b3eef1 100644
--- a/internal/fusefrontend/node_api_check.go
+++ b/internal/fusefrontend/node_api_check.go
@@ -9,3 +9,4 @@ var _ = (fs.NodeLookuper)((*Node)(nil))
 var _ = (fs.NodeReaddirer)((*Node)(nil))
 var _ = (fs.NodeCreater)((*Node)(nil))
 var _ = (fs.NodeMkdirer)((*Node)(nil))
+var _ = (fs.NodeRmdirer)((*Node)(nil))
diff --git a/internal/fusefrontend/node_dir_ops.go b/internal/fusefrontend/node_dir_ops.go
index 0789c92..b4bce1b 100644
--- a/internal/fusefrontend/node_dir_ops.go
+++ b/internal/fusefrontend/node_dir_ops.go
@@ -2,7 +2,10 @@ package fusefrontend
 
 import (
 	"context"
+	"fmt"
+	"io"
 	"path/filepath"
+	"runtime"
 	"syscall"
 
 	"golang.org/x/sys/unix"
@@ -11,6 +14,7 @@ import (
 	"github.com/hanwen/go-fuse/v2/fuse"
 
 	"github.com/rfjakob/gocryptfs/internal/configfile"
+	"github.com/rfjakob/gocryptfs/internal/cryptocore"
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
 	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
 	"github.com/rfjakob/gocryptfs/internal/tlog"
@@ -216,3 +220,127 @@ func (n *Node) Readdir(ctx context.Context) (fs.DirStream, syscall.Errno) {
 
 	return fs.NewListDirStream(plain), 0
 }
+
+// Rmdir - FUSE call.
+//
+// Symlink-safe through Unlinkat() + AT_REMOVEDIR.
+func (n *Node) Rmdir(ctx context.Context, name string) (code syscall.Errno) {
+	rn := n.rootNode()
+	p := filepath.Join(n.path(), name)
+	parentDirFd, cName, err := rn.openBackingDir(p)
+	if err != nil {
+		return fs.ToErrno(err)
+	}
+	defer syscall.Close(parentDirFd)
+	if rn.args.PlaintextNames {
+		// Unlinkat with AT_REMOVEDIR is equivalent to Rmdir
+		err = unix.Unlinkat(parentDirFd, cName, unix.AT_REMOVEDIR)
+		return fs.ToErrno(err)
+	}
+	// Unless we are running as root, we need read, write and execute permissions
+	// to handle gocryptfs.diriv.
+	permWorkaround := false
+	var origMode uint32
+	if !rn.args.PreserveOwner {
+		var st unix.Stat_t
+		err = syscallcompat.Fstatat(parentDirFd, cName, &st, unix.AT_SYMLINK_NOFOLLOW)
+		if err != nil {
+			return fs.ToErrno(err)
+		}
+		if st.Mode&0700 != 0700 {
+			tlog.Debug.Printf("Rmdir: permWorkaround")
+			permWorkaround = true
+			// This cast is needed on Darwin, where st.Mode is uint16.
+			origMode = uint32(st.Mode)
+			err = syscallcompat.FchmodatNofollow(parentDirFd, cName, origMode|0700)
+			if err != nil {
+				tlog.Debug.Printf("Rmdir: permWorkaround: chmod failed: %v", err)
+				return fs.ToErrno(err)
+			}
+		}
+	}
+	dirfd, err := syscallcompat.Openat(parentDirFd, cName,
+		syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NOFOLLOW, 0)
+	if err != nil {
+		tlog.Debug.Printf("Rmdir: Open: %v", err)
+		return fs.ToErrno(err)
+	}
+	defer syscall.Close(dirfd)
+	// Undo the chmod if removing the directory failed. This must run before
+	// closing dirfd, so defer it after (defer is LIFO).
+	if permWorkaround {
+		defer func() {
+			if code != 0 {
+				err = unix.Fchmod(dirfd, origMode)
+				if err != nil {
+					tlog.Warn.Printf("Rmdir: permWorkaround: rollback failed: %v", err)
+				}
+			}
+		}()
+	}
+retry:
+	// Check directory contents
+	children, err := syscallcompat.Getdents(dirfd)
+	if err == io.EOF {
+		// The directory is empty
+		tlog.Warn.Printf("Rmdir: %q: %s is missing", cName, nametransform.DirIVFilename)
+		err = unix.Unlinkat(parentDirFd, cName, unix.AT_REMOVEDIR)
+		return fs.ToErrno(err)
+	}
+	if err != nil {
+		tlog.Warn.Printf("Rmdir: Readdirnames: %v", err)
+		return fs.ToErrno(err)
+	}
+	// MacOS sprinkles .DS_Store files everywhere. This is hard to avoid for
+	// users, so handle it transparently here.
+	if runtime.GOOS == "darwin" && len(children) <= 2 && haveDsstore(children) {
+		err = unix.Unlinkat(dirfd, dsStoreName, 0)
+		if err != nil {
+			tlog.Warn.Printf("Rmdir: failed to delete blocking file %q: %v", dsStoreName, err)
+			return fs.ToErrno(err)
+		}
+		tlog.Warn.Printf("Rmdir: had to delete blocking file %q", dsStoreName)
+		goto retry
+	}
+	// If the directory is not empty besides gocryptfs.diriv, do not even
+	// attempt the dance around gocryptfs.diriv.
+	if len(children) > 1 {
+		return fs.ToErrno(syscall.ENOTEMPTY)
+	}
+	// Move "gocryptfs.diriv" to the parent dir as "gocryptfs.diriv.rmdir.XYZ"
+	tmpName := fmt.Sprintf("%s.rmdir.%d", nametransform.DirIVFilename, cryptocore.RandUint64())
+	tlog.Debug.Printf("Rmdir: Renaming %s to %s", nametransform.DirIVFilename, tmpName)
+	// The directory is in an inconsistent state between rename and rmdir.
+	// Protect against concurrent readers.
+	rn.dirIVLock.Lock()
+	defer rn.dirIVLock.Unlock()
+	err = syscallcompat.Renameat(dirfd, nametransform.DirIVFilename,
+		parentDirFd, tmpName)
+	if err != nil {
+		tlog.Warn.Printf("Rmdir: Renaming %s to %s failed: %v",
+			nametransform.DirIVFilename, tmpName, err)
+		return fs.ToErrno(err)
+	}
+	// Actual Rmdir
+	err = syscallcompat.Unlinkat(parentDirFd, cName, unix.AT_REMOVEDIR)
+	if err != nil {
+		// This can happen if another file in the directory was created in the
+		// meantime, undo the rename
+		err2 := syscallcompat.Renameat(parentDirFd, tmpName,
+			dirfd, nametransform.DirIVFilename)
+		if err2 != nil {
+			tlog.Warn.Printf("Rmdir: Rename rollback failed: %v", err2)
+		}
+		return fs.ToErrno(err)
+	}
+	// Delete "gocryptfs.diriv.rmdir.XYZ"
+	err = syscallcompat.Unlinkat(parentDirFd, tmpName, 0)
+	if err != nil {
+		tlog.Warn.Printf("Rmdir: Could not clean up %s: %v", tmpName, err)
+	}
+	// Delete .name file
+	if nametransform.IsLongContent(cName) {
+		nametransform.DeleteLongNameAt(parentDirFd, cName)
+	}
+	return 0
+}
-- 
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