1 files changed, 209 insertions, 0 deletions
diff --git a/internal/fusefrontend_reverse_v1api/rfile.go b/internal/fusefrontend_reverse_v1api/rfile.go
new file mode 100644
index 0000000..68f7309
--- /dev/null
+++ b/internal/fusefrontend_reverse_v1api/rfile.go
@@ -0,0 +1,209 @@
+package fusefrontend_reverse
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"path/filepath"
+	"syscall"
+
+	// In newer Go versions, this has moved to just "sync/syncmap".
+	"golang.org/x/sync/syncmap"
+
+	"github.com/hanwen/go-fuse/v2/fuse"
+	"github.com/hanwen/go-fuse/v2/fuse/nodefs"
+
+	"github.com/rfjakob/gocryptfs/internal/contentenc"
+	"github.com/rfjakob/gocryptfs/internal/pathiv"
+	"github.com/rfjakob/gocryptfs/internal/syscallcompat"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+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
+	// IV for block 0
+	block0IV []byte
+	// Content encryption helper
+	contentEnc *contentenc.ContentEnc
+}
+
+var inodeTable syncmap.Map
+
+// newFile receives a ciphered path "relPath" and its corresponding
+// decrypted path "pRelPath", opens it and returns a reverseFile
+// object. The backing file descriptor is always read-only.
+func (rfs *ReverseFS) newFile(relPath string, pRelPath string) (*reverseFile, fuse.Status) {
+	if rfs.isExcludedPlain(pRelPath) {
+		// Excluded paths should have been filtered out beforehand. Better safe
+		// than sorry.
+		tlog.Warn.Printf("BUG: newFile: received excluded path %q. This should not happen.", relPath)
+		return nil, fuse.ENOENT
+	}
+	dir := filepath.Dir(pRelPath)
+	dirfd, err := syscallcompat.OpenDirNofollow(rfs.args.Cipherdir, dir)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	fd, err := syscallcompat.Openat(dirfd, filepath.Base(pRelPath), syscall.O_RDONLY|syscall.O_NOFOLLOW, 0)
+	syscall.Close(dirfd)
+	if err != nil {
+		return nil, fuse.ToStatus(err)
+	}
+	var st syscall.Stat_t
+	err = syscall.Fstat(fd, &st)
+	if err != nil {
+		tlog.Warn.Printf("newFile: Fstat error: %v", err)
+		syscall.Close(fd)
+		return nil, fuse.ToStatus(err)
+	}
+	// Reject access if the file descriptor does not refer to a regular file.
+	var a fuse.Attr
+	a.FromStat(&st)
+	if !a.IsRegular() {
+		tlog.Warn.Printf("ino%d: newFile: not a regular file", st.Ino)
+		syscall.Close(fd)
+		return nil, fuse.ToStatus(syscall.EACCES)
+	}
+	// See if we have that inode number already in the table
+	// (even if Nlink has dropped to 1)
+	var derivedIVs pathiv.FileIVs
+	v, found := inodeTable.Load(st.Ino)
+	if found {
+		tlog.Debug.Printf("ino%d: newFile: found in the inode table", st.Ino)
+		derivedIVs = v.(pathiv.FileIVs)
+	} else {
+		derivedIVs = pathiv.DeriveFile(relPath)
+		// Nlink > 1 means there is more than one path to this file.
+		// Store the derived values so we always return the same data,
+		// regardless of the path that is used to access the file.
+		// This means that the first path wins.
+		if st.Nlink > 1 {
+			v, found = inodeTable.LoadOrStore(st.Ino, derivedIVs)
+			if found {
+				// Another thread has stored a different value before we could.
+				derivedIVs = v.(pathiv.FileIVs)
+			} else {
+				tlog.Debug.Printf("ino%d: newFile: Nlink=%d, stored in the inode table", st.Ino, st.Nlink)
+			}
+		}
+	}
+	header := contentenc.FileHeader{
+		Version: contentenc.CurrentVersion,
+		ID:      derivedIVs.ID,
+	}
+	return &reverseFile{
+		File:       nodefs.NewDefaultFile(),
+		fd:         os.NewFile(uintptr(fd), pRelPath),
+		header:     header,
+		block0IV:   derivedIVs.Block0IV,
+		contentEnc: rfs.contentEnc,
+	}, fuse.OK
+}
+
+// GetAttr - FUSE call
+// Triggered by fstat() from userspace
+func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
+	tlog.Debug.Printf("reverseFile.GetAttr fd=%d\n", rf.fd.Fd())
+	// The kernel should fall back to stat()
+	return fuse.ENOSYS
+}
+
+// encryptBlocks - encrypt "plaintext" into a number of ciphertext blocks.
+// "plaintext" must already be block-aligned.
+func (rf *reverseFile) encryptBlocks(plaintext []byte, firstBlockNo uint64, fileID []byte, block0IV []byte) []byte {
+	inBuf := bytes.NewBuffer(plaintext)
+	var outBuf bytes.Buffer
+	bs := int(rf.contentEnc.PlainBS())
+	for blockNo := firstBlockNo; inBuf.Len() > 0; blockNo++ {
+		inBlock := inBuf.Next(bs)
+		iv := pathiv.BlockIV(block0IV, blockNo)
+		outBlock := rf.contentEnc.EncryptBlockNonce(inBlock, blockNo, fileID, iv)
+		outBuf.Write(outBlock)
+	}
+	return outBuf.Bytes()
+}
+
+// readBackingFile: read from the backing plaintext file, encrypt it, return the
+// ciphertext.
+// "off" ... ciphertext offset (must be >= HEADER_LEN)
+// "length" ... ciphertext length
+func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, err error) {
+	blocks := rf.contentEnc.ExplodeCipherRange(off, length)
+
+	// Read the backing plaintext in one go
+	alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
+	plaintext := make([]byte, int(alignedLength))
+	n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
+	if err != nil && err != io.EOF {
+		tlog.Warn.Printf("readBackingFile: ReadAt: %s", err.Error())
+		return nil, err
+	}
+	// Truncate buffer down to actually read bytes
+	plaintext = plaintext[0:n]
+
+	// Encrypt blocks
+	ciphertext := rf.encryptBlocks(plaintext, blocks[0].BlockNo, rf.header.ID, rf.block0IV)
+
+	// Crop down to the relevant part
+	lenHave := len(ciphertext)
+	skip := blocks[0].Skip
+	endWant := int(skip + length)
+	if lenHave > endWant {
+		out = ciphertext[skip:endWant]
+	} else if lenHave > int(skip) {
+		out = ciphertext[skip:lenHave]
+	} // else: out stays empty, file was smaller than the requested offset
+
+	return out, nil
+}
+
+// Read - FUSE call
+func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult, status fuse.Status) {
+	length := uint64(len(buf))
+	off := uint64(ioff)
+	var out bytes.Buffer
+	var header []byte
+
+	// Synthesize file header
+	if off < contentenc.HeaderLen {
+		header = rf.header.Pack()
+		// Truncate to requested part
+		end := int(off) + len(buf)
+		if end > len(header) {
+			end = len(header)
+		}
+		header = header[off:end]
+		// Write into output buffer and adjust offsets
+		out.Write(header)
+		hLen := uint64(len(header))
+		off += hLen
+		length -= hLen
+	}
+
+	// Read actual file data
+	if length > 0 {
+		fileData, err := rf.readBackingFile(off, length)
+		if err != nil {
+			return nil, fuse.ToStatus(err)
+		}
+		if len(fileData) == 0 {
+			// If we could not read any actual data, we also don't want to
+			// return the file header. An empty file stays empty in encrypted
+			// form.
+			return nil, fuse.OK
+		}
+		out.Write(fileData)
+	}
+
+	return fuse.ReadResultData(out.Bytes()), fuse.OK
+}
+
+// Release - FUSE call, close file
+func (rf *reverseFile) Release() {
+	rf.fd.Close()
+}