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package fusefrontend_reverse
import (
"bytes"
"encoding/binary"
"io"
"os"
"syscall"
// In newer Go versions, this has moved to just "sync/syncmap".
"golang.org/x/sync/syncmap"
"github.com/hanwen/go-fuse/fuse"
"github.com/hanwen/go-fuse/fuse/nodefs"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/pathiv"
"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
type derivedIVContainer struct {
id []byte
block0IV []byte
}
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)
}
var st syscall.Stat_t
err = syscall.Fstat(int(fd.Fd()), &st)
if err != nil {
tlog.Warn.Printf("newFile: Fstat error: %v", err)
return nil, fuse.ToStatus(err)
}
// See if we have that inode number already in the table
// (even if Nlink has dropped to 1)
var derivedIVs derivedIVContainer
v, found := inodeTable.Load(st.Ino)
if found {
tlog.Debug.Printf("ino%d: newFile: found in the inode table", st.Ino)
derivedIVs = v.(derivedIVContainer)
} else {
derivedIVs.id = pathiv.Derive(relPath, pathiv.PurposeFileID)
derivedIVs.block0IV = pathiv.Derive(relPath, pathiv.PurposeBlock0IV)
// 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.(derivedIVContainer)
} 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: fd,
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 {
nonce := make([]byte, len(block0IV))
copy(nonce, block0IV)
block0IVlow := binary.BigEndian.Uint64(block0IV[8:])
nonceLow := nonce[8:]
inBuf := bytes.NewBuffer(plaintext)
var outBuf bytes.Buffer
bs := int(rf.contentEnc.PlainBS())
for blockNo := firstBlockNo; inBuf.Len() > 0; blockNo++ {
binary.BigEndian.PutUint64(nonceLow, block0IVlow+blockNo)
inBlock := inBuf.Next(bs)
outBlock := rf.contentEnc.EncryptBlockNonce(inBlock, blockNo, fileID, nonce)
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()
}
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