reverse: implement dynamic diriv

Introduce a unique per-directory diriv that is generated
by hashing the encrypted directory path.

1 files changed, 64 insertions, 49 deletions

diff --git a/internal/fusefrontend_reverse/rfs.go b/internal/fusefrontend_reverse/rfs.go
index 3243dfd..d07971a 100644
--- a/internal/fusefrontend_reverse/rfs.go
+++ b/internal/fusefrontend_reverse/rfs.go
@@ -3,8 +3,7 @@ package fusefrontend_reverse
 import (
 	"fmt"
 	"os"
-	"path"
-	"strings"
+	"path/filepath"
 	"syscall"
 
 	"github.com/hanwen/go-fuse/fuse"
@@ -50,47 +49,59 @@ func NewFS(args fusefrontend.Args) *reverseFS {
 	}
 }
 
-func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
-	// Handle gocryptfs.diriv
-	if relPath == nametransform.DirIVFilename ||
-		strings.HasSuffix(relPath, nametransform.DirIVFilename) {
-
-		fmt.Printf("Handling gocryptfs.diriv\n")
-
-		cDir := path.Dir(relPath)
-		if cDir == "." {
-			cDir = ""
-		}
-		dir, err := rfs.decryptPath(cDir)
-		if err != nil {
-			fmt.Printf("decrypt err %q\n", cDir)
-			return nil, fuse.ToStatus(err)
-		}
-		// Does the parent dir exist?
-		a, status := rfs.loopbackfs.GetAttr(dir, context)
-		if !status.Ok() {
-			fmt.Printf("missing parent\n")
-			return nil, status
-		}
-		// Is it a dir at all?
-		if !a.IsDir() {
-			fmt.Printf("not isdir\n")
-			return nil, fuse.ENOTDIR
-		}
-		// Does the user have execute permissions?
-		if a.Mode&syscall.S_IXUSR == 0 {
-			fmt.Printf("not exec")
-			return nil, fuse.EPERM
-		}
-		// All good. Let's fake the file.
-		// We use the inode number of the parent dir (can this cause problems?).
-		a.Mode = DirIVMode
-		a.Size = nametransform.DirIVLen
-		a.Nlink = 1
-
-		return a, fuse.OK
+// relDir is identical to filepath.Dir excepts that it returns "" when
+// filepath.Dir would return ".".
+// In the FUSE API, the root directory is called "", and we actually want that.
+func relDir(path string) string {
+	dir := filepath.Dir(path)
+	if dir == "." {
+		return ""
+	}
+	return dir
+}
+
+// dirIVAttr handles GetAttr requests for the virtual gocryptfs.diriv files.
+func (rfs *reverseFS) dirIVAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
+	cDir := relDir(relPath)
+	dir, err := rfs.decryptPath(cDir)
+	if err != nil {
+		fmt.Printf("decrypt err %q\n", cDir)
+		return nil, fuse.ToStatus(err)
+	}
+	// Does the parent dir exist?
+	a, status := rfs.loopbackfs.GetAttr(dir, context)
+	if !status.Ok() {
+		fmt.Printf("missing parent\n")
+		return nil, status
+	}
+	// Is it a dir at all?
+	if !a.IsDir() {
+		fmt.Printf("not isdir\n")
+		return nil, fuse.ENOTDIR
+	}
+	// Does the user have execute permissions?
+	if a.Mode&syscall.S_IXUSR == 0 {
+		fmt.Printf("not exec")
+		return nil, fuse.EPERM
 	}
+	// All good. Let's fake the file.
+	// We use the inode number of the parent dir (can this cause problems?).
+	a.Mode = DirIVMode
+	a.Size = nametransform.DirIVLen
+	a.Nlink = 1
 
+	return a, fuse.OK
+}
+
+// isDirIV determines if the path points to a gocryptfs.diriv file
+func isDirIV(relPath string) bool {
+	return filepath.Base(relPath) == nametransform.DirIVFilename
+}
+
+func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
+	if isDirIV(relPath) {
+		return rfs.dirIVAttr(relPath, context)
+	}
 	if rfs.isFiltered(relPath) {
 		return nil, fuse.EPERM
 	}
@@ -110,17 +121,23 @@ func (rfs *reverseFS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr
 }
 
 func (rfs *reverseFS) Access(relPath string, mode uint32, context *fuse.Context) fuse.Status {
+	if isDirIV(relPath) {
+		return fuse.OK
+	}
 	if rfs.isFiltered(relPath) {
 		return fuse.EPERM
 	}
-	cPath, err := rfs.abs(rfs.encryptPath(relPath))
+	absPath, err := rfs.abs(rfs.decryptPath(relPath))
 	if err != nil {
 		return fuse.ToStatus(err)
 	}
-	return fuse.ToStatus(syscall.Access(cPath, mode))
+	return fuse.ToStatus(syscall.Access(absPath, mode))
 }
 
 func (rfs *reverseFS) Open(relPath string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
+	if isDirIV(relPath) {
+		return NewDirIVFile(relPath)
+	}
 	if rfs.isFiltered(relPath) {
 		return nil, fuse.EPERM
 	}
@@ -135,8 +152,8 @@ func (rfs *reverseFS) Open(relPath string, flags uint32, context *fuse.Context)
 	return NewFile(f, rfs.contentEnc)
 }
 
-func (rfs *reverseFS) OpenDir(relPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
-	relPath, err := rfs.decryptPath(relPath)
+func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.DirEntry, fuse.Status) {
+	relPath, err := rfs.decryptPath(cipherPath)
 	if err != nil {
 		return nil, fuse.ToStatus(err)
 	}
@@ -146,11 +163,9 @@ func (rfs *reverseFS) OpenDir(relPath string, context *fuse.Context) ([]fuse.Dir
 		return nil, status
 	}
 	// Encrypt names
+	dirIV := deriveDirIV(cipherPath)
 	for i := range entries {
-		entries[i].Name, err = rfs.encryptPath(entries[i].Name)
-		if err != nil {
-			return nil, fuse.ToStatus(err)
-		}
+		entries[i].Name = rfs.nameTransform.EncryptName(entries[i].Name, dirIV)
 	}
 	// Add virtual gocryptfs.diriv
 	entries = append(entries, fuse.DirEntry{syscall.S_IFREG | 0400, nametransform.DirIVFilename})