122 lines
3.2 KiB
Go
122 lines
3.2 KiB
Go
package fusefrontend_reverse
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import (
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"bytes"
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"fmt"
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"io"
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"os"
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"github.com/hanwen/go-fuse/fuse"
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"github.com/hanwen/go-fuse/fuse/nodefs"
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"github.com/rfjakob/gocryptfs/internal/contentenc"
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"github.com/rfjakob/gocryptfs/internal/tlog"
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)
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// File header that contains an all-zero File ID
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var zeroFileHeader *contentenc.FileHeader
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func init() {
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zeroFileHeader = contentenc.RandomHeader()
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// Overwrite with zeros
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zeroFileHeader.Id = make([]byte, contentenc.HEADER_ID_LEN)
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}
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type reverseFile struct {
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// Embed nodefs.defaultFile for a ENOSYS implementation of all methods
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nodefs.File
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// Backing FD
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fd *os.File
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// Content encryption helper
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contentEnc *contentenc.ContentEnc
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}
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func NewFile(fd *os.File, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
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return &reverseFile{
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File: nodefs.NewDefaultFile(),
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fd: fd,
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contentEnc: contentEnc,
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}, fuse.OK
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}
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// GetAttr - FUSE call
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func (rf *reverseFile) GetAttr(*fuse.Attr) fuse.Status {
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fmt.Printf("reverseFile.GetAttr fd=%d\n", rf.fd.Fd())
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return fuse.ENOSYS
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}
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// readBackingFile: read from the backing plaintext file, encrypt it, return the
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// ciphertext.
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// "off" ... ciphertext offset (must be >= HEADER_LEN)
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// "length" ... ciphertext length
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func (rf *reverseFile) readBackingFile(off uint64, length uint64) (out []byte, err error) {
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blocks := rf.contentEnc.ExplodeCipherRange(off, length)
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// Read the backing plaintext in one go
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alignedOffset, alignedLength := contentenc.JointPlaintextRange(blocks)
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plaintext := make([]byte, int(alignedLength))
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n, err := rf.fd.ReadAt(plaintext, int64(alignedOffset))
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if err != nil && err != io.EOF {
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tlog.Warn.Printf("readBackingFile: ReadAt: %s", err.Error())
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return nil, err
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}
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// Truncate buffer down to actually read bytes
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plaintext = plaintext[0:n]
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// Encrypt blocks
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ciphertext := rf.contentEnc.EncryptBlocks(plaintext, blocks[0].BlockNo, zeroFileHeader.Id, contentenc.ReverseDummyNonce)
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// Crop down to the relevant part
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lenHave := len(ciphertext)
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skip := blocks[0].Skip
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endWant := int(skip + length)
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if lenHave > endWant {
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out = ciphertext[skip:endWant]
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} else if lenHave > int(skip) {
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out = ciphertext[skip:lenHave]
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} // else: out stays empty, file was smaller than the requested offset
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return out, nil
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}
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// Read - FUSE call
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func (rf *reverseFile) Read(buf []byte, ioff int64) (resultData fuse.ReadResult, status fuse.Status) {
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length := uint64(len(buf))
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off := uint64(ioff)
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var out bytes.Buffer
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var header []byte
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// Synthesize file header
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if off < contentenc.HEADER_LEN {
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header = zeroFileHeader.Pack()
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// Truncate to requested part
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end := int(off) + len(buf)
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if end > len(header) {
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end = len(header)
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}
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header = header[off:end]
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// Write into output buffer and adjust offsets
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out.Write(header)
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hLen := uint64(len(header))
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off += hLen
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length -= hLen
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}
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// Read actual file data
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if length > 0 {
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fileData, err := rf.readBackingFile(off, length)
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if err != nil {
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return nil, fuse.ToStatus(err)
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}
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if len(fileData) == 0 {
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// If we could not read any actual data, we also don't want to
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// return the file header. An empty file stays empty in encrypted
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// form.
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return nil, fuse.OK
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}
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out.Write(fileData)
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}
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return fuse.ReadResultData(out.Bytes()), fuse.OK
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}
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