reverse: derive file ID and block IVs from file paths

6 files changed, 41 insertions, 37 deletions

diff --git a/internal/contentenc/content.go b/internal/contentenc/content.go
index c638221..98037d0 100644
--- a/internal/contentenc/content.go
+++ b/internal/contentenc/content.go
@@ -19,9 +19,9 @@ const (
 	// We always use 128-bit IVs for file content encryption
 	IVBitLen = 128
 
-	_                           = iota // skip zero
-	RandomNonce       NonceMode = iota
-	ReverseDummyNonce NonceMode = iota
+	_                                   = iota // skip zero
+	RandomNonce               NonceMode = iota
+	ReverseDeterministicNonce NonceMode = iota
 )
 
 type ContentEnc struct {
@@ -147,12 +147,17 @@ func (be *ContentEnc) EncryptBlock(plaintext []byte, blockNo uint64, fileID []by
 
 	var nonce []byte
 	switch nMode {
-	case ReverseDummyNonce:
+	case ReverseDeterministicNonce:
 		if be.cryptoCore.AEADBackend != cryptocore.BackendGCMSIV {
-			panic("MUST NOT use dummy nonces unless in GCMSIV mode!")
+			panic("MUST NOT use deterministic nonces unless in GCMSIV mode!")
 		}
-		nonce = make([]byte, IVBitLen/8)
-		binary.BigEndian.PutUint64(nonce, blockNo)
+		l := IVBitLen / 8
+		nonce = make([]byte, l)
+		copy(nonce, fileID)
+		// Add the block number to the last 8 byte. Plus one so the block-zero
+		// IV is distinct from the fileID.
+		counter := binary.BigEndian.Uint64(nonce[l-8 : l])
+		binary.BigEndian.PutUint64(nonce[l-8:l], counter+blockNo+1)
 	case RandomNonce:
 		// Get a fresh random nonce
 		nonce = be.cryptoCore.IVGenerator.Get()
diff --git a/internal/fusefrontend_reverse/reverse_diriv.go b/internal/fusefrontend_reverse/reverse_diriv.go
index df3a4d1..88d0680 100644
--- a/internal/fusefrontend_reverse/reverse_diriv.go
+++ b/internal/fusefrontend_reverse/reverse_diriv.go
@@ -9,10 +9,9 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/nametransform"
 )
 
-// deriveDirIV derives the DirIV from the encrypted directory path by
-// hashing it
-func deriveDirIV(dirPath string) []byte {
-	hash := sha256.Sum256([]byte(dirPath))
+// derivePathIV derives an IV from an encrypted path by hashing it
+func derivePathIV(path string) []byte {
+	hash := sha256.Sum256([]byte(path))
 	return hash[:nametransform.DirIVLen]
 }
 
@@ -22,5 +21,5 @@ func (rfs *reverseFS) newDirIVFile(cRelPath string) (nodefs.File, fuse.Status) {
 	if err != nil {
 		return nil, fuse.ToStatus(err)
 	}
-	return rfs.NewVirtualFile(deriveDirIV(cDir), absDir)
+	return rfs.NewVirtualFile(derivePathIV(cDir), absDir)
 }
diff --git a/internal/fusefrontend_reverse/reverse_longnames.go b/internal/fusefrontend_reverse/reverse_longnames.go
index 487802f..9c45fe8 100644
--- a/internal/fusefrontend_reverse/reverse_longnames.go
+++ b/internal/fusefrontend_reverse/reverse_longnames.go
@@ -89,7 +89,7 @@ func (rfs *reverseFS) newNameFile(relPath string) (nodefs.File, fuse.Status) {
 	if err != nil {
 		return nil, fuse.ToStatus(err)
 	}
-	dirIV := deriveDirIV(cDir)
+	dirIV := derivePathIV(cDir)
 	e, err := rfs.findLongnameParent(pDir, dirIV, longname)
 	if err != nil {
 		return nil, fuse.ToStatus(err)
diff --git a/internal/fusefrontend_reverse/rfile.go b/internal/fusefrontend_reverse/rfile.go
index 7e54b17..4e9b5ba 100644
--- a/internal/fusefrontend_reverse/rfile.go
+++ b/internal/fusefrontend_reverse/rfile.go
@@ -13,29 +13,32 @@ import (
 	"github.com/rfjakob/gocryptfs/internal/tlog"
 )
 
-// File header that contains an all-zero File ID
-var zeroFileHeader *contentenc.FileHeader
-
-func init() {
-	zeroFileHeader = contentenc.RandomHeader()
-	// Overwrite with zeros
-	zeroFileHeader.Id = make([]byte, contentenc.HEADER_ID_LEN)
-}
-
 type reverseFile struct {
 	// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
 	nodefs.File
 	// Backing FD
 	fd *os.File
+	// File header (contains the IV)
+	header contentenc.FileHeader
 	// Content encryption helper
 	contentEnc *contentenc.ContentEnc
 }
 
-func NewFile(fd *os.File, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
+func (rfs *reverseFS) NewFile(relPath string, flags uint32) (nodefs.File, fuse.Status) {
+	absPath, err := rfs.abs(rfs.decryptPath(relPath))
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	fd, err := os.OpenFile(absPath, int(flags), 0666)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	id := derivePathIV(relPath)
 	return &reverseFile{
 		File:       nodefs.NewDefaultFile(),
 		fd:         fd,
-		contentEnc: contentEnc,
+		header:     contentenc.FileHeader{contentenc.CurrentVersion, id},
+		contentEnc: rfs.contentEnc,
 	}, fuse.OK
 }
 
@@ -64,7 +67,7 @@ func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, e
 	plaintext = plaintext[0:n]
 
 	// Encrypt blocks
-	ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, zeroFileHeader.Id, contentenc.ReverseDummyNonce)
+	ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, rf.header.Id, contentenc.ReverseDeterministicNonce)
 
 	// Crop down to the relevant part
 	lenHave := len(ciphertext)
@@ -88,7 +91,7 @@ func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult,
 
 	// Synthesize file header
 	if off < contentenc.HEADER_LEN {
-		header = zeroFileHeader.Pack()
+		header = rf.header.Pack()
 		// Truncate to requested part
 		end := int(off) + len(buf)
 		if end > len(header) {
@@ -119,3 +122,8 @@ func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult,
 
 	return fuse.ReadResultData(out.Bytes()), fuse.OK
 }
+
+// Release - FUSE call, close file
+func (rf *reverseFile) Release() {
+	rf.fd.Close()
+}
diff --git a/internal/fusefrontend_reverse/rfs.go b/internal/fusefrontend_reverse/rfs.go
index 9ebf91c..6089d41 100644
--- a/internal/fusefrontend_reverse/rfs.go
+++ b/internal/fusefrontend_reverse/rfs.go
@@ -226,15 +226,7 @@ func (rfs *reverseFS) Open(relPath string, flags uint32, context *fuse.Context)
 	if rfs.isFiltered(relPath) {
 		return nil, fuse.EPERM
 	}
-	absPath, err := rfs.abs(rfs.decryptPath(relPath))
-	if err != nil {
-		return nil, fuse.ToStatus(err)
-	}
-	f, err := os.OpenFile(absPath, int(flags), 0666)
-	if err != nil {
-		return nil, fuse.ToStatus(err)
-	}
-	return NewFile(f, rfs.contentEnc)
+	return rfs.NewFile(relPath, flags)
 }
 
 // OpenDir - FUSE readdir call
@@ -258,7 +250,7 @@ func (rfs *reverseFS) OpenDir(cipherPath string, context *fuse.Context) ([]fuse.
 	nVirtual := 1
 
 	// Encrypt names
-	dirIV := deriveDirIV(cipherPath)
+	dirIV := derivePathIV(cipherPath)
 	for i := range entries {
 		var cName string
 		// ".gocryptfs.reverse.conf" in the root directory is mapped to "gocryptfs.conf"
diff --git a/internal/fusefrontend_reverse/rpath.go b/internal/fusefrontend_reverse/rpath.go
index 19539bb..c603cad 100644
--- a/internal/fusefrontend_reverse/rpath.go
+++ b/internal/fusefrontend_reverse/rpath.go
@@ -36,7 +36,7 @@ func (rfs *reverseFS) decryptPath(relPath string) (string, error) {
 		// Start at the top and recurse
 		currentDir := filepath.Join(parts[:i]...)
 		nameType := nametransform.NameType(part)
-		dirIV := deriveDirIV(currentDir)
+		dirIV := derivePathIV(currentDir)
 		var transformedPart string
 		if nameType == nametransform.LongNameNone {
 			transformedPart, err = rfs.nameTransform.DecryptName(part, dirIV)