Refactor ciphertext <-> plaintext offset translation functions

Move all the intelligence into the new file address_translation.go.
That the calculations were spread out too much became apparent when adding
the file header. This should make the code much easier to modify in the
future.

cryptfs/address_translation.go

@@ -0,0 +1,79 @@
+package cryptfs
+
+// CryptFS methods that translate offsets between ciphertext and plaintext
+
+// get the block number at plain-text offset
+func (be *CryptFS) PlainOffToBlockNo(plainOffset uint64) uint64 {
+	return plainOffset / be.plainBS
+}
+
+// get the block number at ciphter-text offset
+func (be *CryptFS) CipherOffToBlockNo(cipherOffset uint64) uint64 {
+	return (cipherOffset - HEADER_LEN) / be.cipherBS
+}
+
+// get ciphertext offset of block "blockNo"
+func (be *CryptFS) BlockNoToCipherOff(blockNo uint64) uint64 {
+	return HEADER_LEN + blockNo*be.cipherBS
+}
+
+// get plaintext offset of block "blockNo"
+func (be *CryptFS) BlockNoToPlainOff(blockNo uint64) uint64 {
+	return blockNo * be.plainBS
+}
+
+// PlainSize - calculate plaintext size from ciphertext size
+func (be *CryptFS) CipherSizeToPlainSize(cipherSize uint64) uint64 {
+
+	// Zero sized files stay zero-sized
+	if cipherSize == 0 {
+		return 0
+	}
+
+	// Block number at last byte
+	blockNo := be.CipherOffToBlockNo(cipherSize - 1)
+	blockCount := blockNo + 1
+
+	overhead := BLOCK_OVERHEAD*blockCount + HEADER_LEN
+
+	return cipherSize - overhead
+}
+
+// CipherSize - calculate ciphertext size from plaintext size
+func (be *CryptFS) PlainSizeToCipherSize(plainSize uint64) uint64 {
+
+	// Block number at last byte
+	blockNo := be.PlainOffToBlockNo(plainSize - 1)
+	blockCount := blockNo + 1
+
+	overhead := BLOCK_OVERHEAD*blockCount + HEADER_LEN
+
+	return plainSize + overhead
+}
+
+// Split a plaintext byte range into (possibly partial) blocks
+func (be *CryptFS) ExplodePlainRange(offset uint64, length uint64) []intraBlock {
+	var blocks []intraBlock
+	var nextBlock intraBlock
+	nextBlock.fs = be
+
+	for length > 0 {
+		nextBlock.BlockNo = be.PlainOffToBlockNo(offset)
+		nextBlock.Skip = offset - be.BlockNoToPlainOff(nextBlock.BlockNo)
+
+		// Minimum of remaining data and remaining space in the block
+		nextBlock.Length = MinUint64(length, be.plainBS-nextBlock.Skip)
+
+		blocks = append(blocks, nextBlock)
+		offset += nextBlock.Length
+		length -= nextBlock.Length
+	}
+	return blocks
+}
+
+func MinUint64(x uint64, y uint64) uint64 {
+	if x < y {
+		return x
+	}
+	return y
+}

cryptfs/config_file.go

@@ -1,8 +1,8 @@
 package cryptfs
 
 import (
-	"fmt"
 	"encoding/json"
+	"fmt"
 	"io/ioutil"
 )
 import "os"

cryptfs/content_test.go

@@ -24,7 +24,7 @@ func TestSplitRange(t *testing.T) {
 	f := NewCryptFS(key, true)
 
 	for _, r := range ranges {
-		parts := f.SplitRange(r.offset, r.length)
+		parts := f.ExplodePlainRange(r.offset, r.length)
 		var lastBlockNo uint64 = 1 << 63
 		for _, p := range parts {
 			if p.BlockNo == lastBlockNo {
@@ -51,7 +51,11 @@ func TestCiphertextRange(t *testing.T) {
 	f := NewCryptFS(key, true)
 
 	for _, r := range ranges {
-		alignedOffset, alignedLength, skipBytes := f.CiphertextRange(r.offset, r.length)
+
+		blocks := f.ExplodePlainRange(r.offset, r.length)
+		alignedOffset, alignedLength := blocks[0].JointCiphertextRange(blocks)
+		skipBytes := blocks[0].Skip
+
 		if alignedLength < r.length {
 			t.Errorf("alignedLength=%s is smaller than length=%d", alignedLength, r.length)
 		}
@@ -68,19 +72,19 @@ func TestBlockNo(t *testing.T) {
 	key := make([]byte, KEY_LEN)
 	f := NewCryptFS(key, true)
 
-	b := f.BlockNoCipherOff(788)
+	b := f.CipherOffToBlockNo(788)
 	if b != 0 {
 		t.Errorf("actual: %d", b)
 	}
-	b = f.BlockNoCipherOff(HEADER_LEN + f.CipherBS())
+	b = f.CipherOffToBlockNo(HEADER_LEN + f.cipherBS)
 	if b != 1 {
 		t.Errorf("actual: %d", b)
 	}
-	b = f.BlockNoPlainOff(788)
+	b = f.PlainOffToBlockNo(788)
 	if b != 0 {
 		t.Errorf("actual: %d", b)
 	}
-	b = f.BlockNoPlainOff(f.PlainBS())
+	b = f.PlainOffToBlockNo(f.plainBS)
 	if b != 1 {
 		t.Errorf("actual: %d", b)
 	}

cryptfs/cryptfs.go

@@ -61,8 +61,3 @@ func NewCryptFS(key []byte, useOpenssl bool) *CryptFS {
 func (be *CryptFS) PlainBS() uint64 {
 	return be.plainBS
 }
-
-// Get ciphertext block size
-func (be *CryptFS) CipherBS() uint64 {
-	return be.cipherBS
-}

cryptfs/cryptfs_content.go

@@ -12,11 +12,6 @@ import (
 	"os"
 )
 
-const (
-	// A block of 4124 zero bytes has this md5
-	ZeroBlockMd5 = "64331af89bd15a987b39855338336237"
-)
-
 // md5sum - debug helper, return md5 hex string
 func md5sum(buf []byte) string {
 	rawHash := md5.Sum(buf)
@@ -110,106 +105,6 @@ func (be *CryptFS) EncryptBlock(plaintext []byte, blockNo uint64, fileId []byte)
 	return ciphertext
 }
 
-// Split a plaintext byte range into (possibly partial) blocks
-func (be *CryptFS) SplitRange(offset uint64, length uint64) []intraBlock {
-	var b intraBlock
-	var parts []intraBlock
-
-	b.fs = be
-
-	for length > 0 {
-		b.BlockNo = offset / be.plainBS
-		b.Skip = offset % be.plainBS
-		// Minimum of remaining data and remaining space in the block
-		b.Length = be.minu64(length, be.plainBS-b.Skip)
-		parts = append(parts, b)
-		offset += b.Length
-		length -= b.Length
-	}
-	return parts
-}
-
-// PlainSize - calculate plaintext size from ciphertext size
-func (be *CryptFS) PlainSize(size uint64) uint64 {
-
-	// Zero sized files stay zero-sized
-	if size == 0 {
-		return 0
-	}
-
-	// Account for header
-	size -= HEADER_LEN
-
-	overhead := be.cipherBS - be.plainBS
-	nBlocks := (size + be.cipherBS - 1) / be.cipherBS
-	if nBlocks*overhead > size {
-		Warn.Printf("PlainSize: Negative size, returning 0 instead\n")
-		return 0
-	}
-	size -= nBlocks * overhead
-
-	return size
-}
-
-// CipherSize - calculate ciphertext size from plaintext size
-func (be *CryptFS) CipherSize(size uint64) uint64 {
-	overhead := be.cipherBS - be.plainBS
-	nBlocks := (size + be.plainBS - 1) / be.plainBS
-	size += nBlocks * overhead
-
-	return size
-}
-
-func (be *CryptFS) minu64(x uint64, y uint64) uint64 {
-	if x < y {
-		return x
-	}
-	return y
-}
-
-// CiphertextRange - Get byte range in backing ciphertext corresponding
-// to plaintext range. Returns a range aligned to ciphertext blocks.
-func (be *CryptFS) CiphertextRange(offset uint64, length uint64) (alignedOffset uint64, alignedLength uint64, skipBytes int) {
-	// Decrypting the ciphertext will yield too many plaintext bytes. Skip this number
-	// of bytes from the front.
-	skip := offset % be.plainBS
-
-	firstBlockNo := offset / be.plainBS
-	lastBlockNo := (offset + length - 1) / be.plainBS
-
-	alignedOffset = HEADER_LEN + firstBlockNo * be.cipherBS
-	alignedLength = (lastBlockNo - firstBlockNo + 1) * be.cipherBS
-
-	skipBytes = int(skip)
-	return alignedOffset, alignedLength, skipBytes
-}
-
-// Get the byte range in the ciphertext corresponding to blocks
-// (full blocks!)
-func (be *CryptFS) JoinCiphertextRange(blocks []intraBlock) (uint64, uint64) {
-
-	offset, _ := blocks[0].CiphertextRange()
-	last := blocks[len(blocks)-1]
-	length := (last.BlockNo - blocks[0].BlockNo + 1) * be.cipherBS
-
-	return offset, length
-}
-
-// Crop plaintext that correspons to complete cipher blocks down to what is
-// requested according to "iblocks"
-func (be *CryptFS) CropPlaintext(plaintext []byte, blocks []intraBlock) []byte {
-	offset := blocks[0].Skip
-	last := blocks[len(blocks)-1]
-	length := (last.BlockNo - blocks[0].BlockNo + 1) * be.plainBS
-	var cropped []byte
-	if offset+length > uint64(len(plaintext)) {
-		cropped = plaintext[offset:]
-	} else {
-		cropped = plaintext[offset : offset+length]
-	}
-	return cropped
-}
-
 // MergeBlocks - Merge newData into oldData at offset
 // New block may be bigger than both newData and oldData
 func (be *CryptFS) MergeBlocks(oldData []byte, newData []byte, offset int) []byte {
@@ -230,13 +125,3 @@ func (be *CryptFS) MergeBlocks(oldData []byte, newData []byte, offset int) []byt
 	}
 	return out[0:outLen]
 }
-
-// Get the block number at plain-text offset
-func (be *CryptFS) BlockNoPlainOff(plainOffset uint64) uint64 {
-	return plainOffset / be.plainBS
-}
-
-// Get the block number at ciphter-text offset
-func (be *CryptFS) BlockNoCipherOff(cipherOffset uint64) uint64 {
-	return (cipherOffset - HEADER_LEN) / be.cipherBS
-}

cryptfs/intrablock.go

@@ -19,13 +19,13 @@ func (ib *intraBlock) IsPartial() bool {
 // CiphertextRange - get byte range in ciphertext file corresponding to BlockNo
 // (complete block)
 func (ib *intraBlock) CiphertextRange() (offset uint64, length uint64) {
-	return HEADER_LEN + ib.BlockNo * ib.fs.cipherBS, ib.fs.cipherBS
+	return ib.fs.BlockNoToCipherOff(ib.BlockNo), ib.fs.cipherBS
 }
 
 // PlaintextRange - get byte range in plaintext corresponding to BlockNo
 // (complete block)
 func (ib *intraBlock) PlaintextRange() (offset uint64, length uint64) {
-	return ib.BlockNo * ib.fs.plainBS, ib.fs.plainBS
+	return ib.fs.BlockNoToPlainOff(ib.BlockNo), ib.fs.plainBS
 }
 
 // CropBlock - crop a potentially larger plaintext block down to the relevant part
@@ -37,3 +37,15 @@ func (ib *intraBlock) CropBlock(d []byte) []byte {
 	}
 	return d[ib.Skip:lenWant]
 }
+
+// Ciphertext range corresponding to the sum of all "blocks" (complete blocks)
+func (ib *intraBlock) JointCiphertextRange(blocks []intraBlock) (offset uint64, length uint64) {
+	firstBlock := blocks[0]
+	lastBlock := blocks[len(blocks)-1]
+
+	offset = ib.fs.BlockNoToCipherOff(firstBlock.BlockNo)
+	offsetLast := ib.fs.BlockNoToCipherOff(lastBlock.BlockNo)
+	length = offsetLast + ib.fs.cipherBS - offset
+
+	return offset, length
+}

main_test.go

@@ -1,8 +1,6 @@
 package main
 
 import (
-	"runtime"
-	"sync"
 	"bytes"
 	"crypto/md5"
 	"encoding/hex"
@@ -11,6 +9,8 @@ import (
 	"io/ioutil"
 	"os"
 	"os/exec"
+	"runtime"
+	"sync"
 	"testing"
 )
 

pathfs_frontend/file.go

@@ -128,8 +128,10 @@ func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
 	}
 
 	// Read the backing ciphertext in one go
-	alignedOffset, alignedLength, skip := f.cfs.CiphertextRange(off, length)
-	cryptfs.Debug.Printf("CiphertextRange(%d, %d) -> %d, %d, %d\n", off, length, alignedOffset, alignedLength, skip)
+	blocks := f.cfs.ExplodePlainRange(off, length)
+	alignedOffset, alignedLength := blocks[0].JointCiphertextRange(blocks)
+	skip := blocks[0].Skip
+	cryptfs.Debug.Printf("JointCiphertextRange(%d, %d) -> %d, %d, %d\n", off, length, alignedOffset, alignedLength, skip)
 	ciphertext := make([]byte, int(alignedLength))
 	f.fdLock.Lock()
 	n, err := f.fd.ReadAt(ciphertext, int64(alignedOffset))
@@ -141,27 +143,27 @@ func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
 	// Truncate ciphertext buffer down to actually read bytes
 	ciphertext = ciphertext[0:n]
 
-	blockNo := (alignedOffset - cryptfs.HEADER_LEN) / f.cfs.CipherBS()
-	cryptfs.Debug.Printf("ReadAt offset=%d bytes (%d blocks), want=%d, got=%d\n", alignedOffset, blockNo, alignedLength, n)
+	firstBlockNo := blocks[0].BlockNo
+	cryptfs.Debug.Printf("ReadAt offset=%d bytes (%d blocks), want=%d, got=%d\n", alignedOffset, firstBlockNo, alignedLength, n)
 
 	// Decrypt it
-	plaintext, err := f.cfs.DecryptBlocks(ciphertext, blockNo, f.header.Id)
+	plaintext, err := f.cfs.DecryptBlocks(ciphertext, firstBlockNo, f.header.Id)
 	if err != nil {
-		blockNo := (alignedOffset + uint64(len(plaintext))) / f.cfs.PlainBS()
-		cipherOff := cryptfs.HEADER_LEN + blockNo * f.cfs.CipherBS()
-		plainOff := blockNo * f.cfs.PlainBS()
-		cryptfs.Warn.Printf("ino%d: doRead: corrupt block #%d (plainOff=%d/%d, cipherOff=%d/%d)\n",
-			f.ino, blockNo, plainOff, f.cfs.PlainBS(), cipherOff, f.cfs.CipherBS())
+		curruptBlockNo := firstBlockNo + f.cfs.PlainOffToBlockNo(uint64(len(plaintext)))
+		cipherOff := f.cfs.BlockNoToCipherOff(curruptBlockNo)
+		plainOff := f.cfs.BlockNoToPlainOff(curruptBlockNo)
+		cryptfs.Warn.Printf("ino%d: doRead: corrupt block #%d (plainOff=%d, cipherOff=%d)\n",
+			f.ino, curruptBlockNo, plainOff, cipherOff)
 		return nil, fuse.EIO
 	}
 
 	// Crop down to the relevant part
 	var out []byte
 	lenHave := len(plaintext)
-	lenWant := skip + int(length)
+	lenWant := int(skip + length)
 	if lenHave > lenWant {
-		out = plaintext[skip : skip+int(length)]
-	} else if lenHave > skip {
+		out = plaintext[skip:lenWant]
+	} else if lenHave > int(skip) {
 		out = plaintext[skip:lenHave]
 	}
 	// else: out stays empty, file was smaller than the requested offset
@@ -216,7 +218,7 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 	var written uint32
 	status := fuse.OK
 	dataBuf := bytes.NewBuffer(data)
-	blocks := f.cfs.SplitRange(uint64(off), uint64(len(data)))
+	blocks := f.cfs.ExplodePlainRange(uint64(off), uint64(len(data)))
 	for _, b := range blocks {
 
 		blockData := dataBuf.Next(int(b.Length))
@@ -240,10 +242,6 @@ func (f *file) doWrite(data []byte, off int64) (uint32, fuse.Status) {
 		blockData = f.cfs.EncryptBlock(blockData, b.BlockNo, f.header.Id)
 		cryptfs.Debug.Printf("ino%d: Writing %d bytes to block #%d, md5=%s\n",
 			f.ino, len(blockData)-cryptfs.BLOCK_OVERHEAD, b.BlockNo, cryptfs.Debug.Md5sum(blockData))
-		if len(blockData) != int(f.cfs.CipherBS()) {
-			cryptfs.Debug.Printf("ino%d: Writing partial block #%d (%d bytes)\n",
-				f.ino, b.BlockNo, len(blockData) - cryptfs.BLOCK_OVERHEAD)
-		}
 		f.fdLock.Lock()
 		_, err := f.fd.WriteAt(blockData, int64(blockOffset))
 		f.fdLock.Unlock()
@@ -267,7 +265,7 @@ func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
 		cryptfs.Warn.Printf("Write: Fstat failed: %v\n", err)
 		return 0, fuse.ToStatus(err)
 	}
-	plainSize := f.cfs.PlainSize(uint64(fi.Size()))
+	plainSize := f.cfs.CipherSizeToPlainSize(uint64(fi.Size()))
 	if f.createsHole(plainSize, off) {
 		status := f.zeroPad(plainSize)
 		if status != fuse.OK {
@@ -332,7 +330,7 @@ func (f *file) Truncate(newSize uint64) fuse.Status {
 		cryptfs.Warn.Printf("Truncate: Fstat failed: %v\n", err)
 		return fuse.ToStatus(err)
 	}
-	oldSize := f.cfs.PlainSize(uint64(fi.Size()))
+	oldSize := f.cfs.CipherSizeToPlainSize(uint64(fi.Size()))
 	{
 		oldB := float32(oldSize) / float32(f.cfs.PlainBS())
 		newB := float32(newSize) / float32(f.cfs.PlainBS())
@@ -350,7 +348,7 @@ func (f *file) Truncate(newSize uint64) fuse.Status {
 			}
 		}
 
-		blocks := f.cfs.SplitRange(oldSize, newSize-oldSize)
+		blocks := f.cfs.ExplodePlainRange(oldSize, newSize-oldSize)
 		for _, b := range blocks {
 			// First and last block may be partial
 			if b.IsPartial() {
@@ -374,9 +372,9 @@ func (f *file) Truncate(newSize uint64) fuse.Status {
 		return fuse.OK
 	} else {
 		// File shrinks
-		blockNo := f.cfs.BlockNoPlainOff(newSize)
-		cipherOff := cryptfs.HEADER_LEN + blockNo * f.cfs.CipherBS()
-		plainOff := blockNo * f.cfs.PlainBS()
+		blockNo := f.cfs.PlainOffToBlockNo(newSize)
+		cipherOff := f.cfs.BlockNoToCipherOff(blockNo)
+		plainOff := f.cfs.BlockNoToPlainOff(blockNo)
 		lastBlockLen := newSize - plainOff
 		var data []byte
 		if lastBlockLen > 0 {
@@ -430,7 +428,7 @@ func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
 		return fuse.ToStatus(err)
 	}
 	a.FromStat(&st)
-	a.Size = f.cfs.PlainSize(a.Size)
+	a.Size = f.cfs.CipherSizeToPlainSize(a.Size)
 
 	return fuse.OK
 }

pathfs_frontend/file_holes.go

@@ -7,8 +7,8 @@ import (
 
 // Will a write to offset "off" create a file hole?
 func (f *file) createsHole(plainSize uint64, off int64) bool {
-	nextBlock := f.cfs.BlockNoPlainOff(plainSize)
-	targetBlock := f.cfs.BlockNoPlainOff(uint64(off))
+	nextBlock := f.cfs.PlainOffToBlockNo(plainSize)
+	targetBlock := f.cfs.PlainOffToBlockNo(uint64(off))
 	if targetBlock > nextBlock {
 		return true
 	}

pathfs_frontend/fs.go

@@ -41,7 +41,7 @@ func (fs *FS) GetAttr(name string, context *fuse.Context) (*fuse.Attr, fuse.Stat
 		return a, status
 	}
 	if a.IsRegular() {
-		a.Size = fs.PlainSize(a.Size)
+		a.Size = fs.CipherSizeToPlainSize(a.Size)
 	} else if a.IsSymlink() {
 		target, _ := fs.Readlink(name, context)
 		a.Size = uint64(len(target))

test.bash

@@ -2,11 +2,10 @@
 
 set -eux
 
-cd cryptfs
-go build
-go test
-cd ..
+for i in ./cryptfs .
+do
 
-go build
-go test
+	go build $i
+	go test $i
+done