libgocryptfs/internal/fusefrontend/file.go

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package fusefrontend
// FUSE operations on file handles
import (
"bytes"
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"context"
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"encoding/hex"
"fmt"
"io"
"log"
"os"
"sync"
"syscall"
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"github.com/hanwen/go-fuse/v2/fs"
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"github.com/hanwen/go-fuse/v2/fuse"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/inomap"
"github.com/rfjakob/gocryptfs/internal/openfiletable"
"github.com/rfjakob/gocryptfs/internal/serialize_reads"
"github.com/rfjakob/gocryptfs/internal/stupidgcm"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// File implements the go-fuse v2 API (github.com/hanwen/go-fuse/v2/fs)
type File struct {
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fd *os.File
// Has Release() already been called on this file? This also means that the
// wlock entry has been freed, so let's not crash trying to access it.
// Due to concurrency, Release can overtake other operations. These will
// return EBADF in that case.
released bool
// fdLock prevents the fd to be closed while we are in the middle of
// an operation.
// Every FUSE entrypoint should RLock(). The only user of Lock() is
// Release(), which closes the fd and sets "released" to true.
fdLock sync.RWMutex
// Content encryption helper
contentEnc *contentenc.ContentEnc
// Device and inode number uniquely identify the backing file
qIno inomap.QIno
// Entry in the open file table
fileTableEntry *openfiletable.Entry
// Store where the last byte was written
lastWrittenOffset int64
// The opCount is used to judge whether "lastWrittenOffset" is still
// guaranteed to be correct.
lastOpCount uint64
// Parent filesystem
rootNode *RootNode
}
// NewFile returns a new go-fuse File instance.
func NewFile(fd *os.File, rn *RootNode, st *syscall.Stat_t) *File {
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qi := inomap.QInoFromStat(st)
e := openfiletable.Register(qi)
return &File{
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fd: fd,
contentEnc: rn.contentEnc,
qIno: qi,
fileTableEntry: e,
rootNode: rn,
}
}
// intFd - return the backing file descriptor as an integer.
func (f *File) intFd() int {
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return int(f.fd.Fd())
}
// readFileID loads the file header from disk and extracts the file ID.
// Returns io.EOF if the file is empty.
func (f *File) readFileID() ([]byte, error) {
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// We read +1 byte to determine if the file has actual content
// and not only the header. A header-only file will be considered empty.
// This makes File ID poisoning more difficult.
readLen := contentenc.HeaderLen + 1
buf := make([]byte, readLen)
n, err := f.fd.ReadAt(buf, 0)
if err != nil {
if err == io.EOF && n != 0 {
tlog.Warn.Printf("readFileID %d: incomplete file, got %d instead of %d bytes",
f.qIno.Ino, n, readLen)
f.rootNode.reportMitigatedCorruption(fmt.Sprint(f.qIno.Ino))
}
return nil, err
}
buf = buf[:contentenc.HeaderLen]
h, err := contentenc.ParseHeader(buf)
if err != nil {
return nil, err
}
return h.ID, nil
}
// createHeader creates a new random header and writes it to disk.
// Returns the new file ID.
// The caller must hold fileIDLock.Lock().
func (f *File) createHeader() (fileID []byte, err error) {
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h := contentenc.RandomHeader()
buf := h.Pack()
// Prevent partially written (=corrupt) header by preallocating the space beforehand
if !f.rootNode.args.NoPrealloc {
err = syscallcompat.EnospcPrealloc(f.intFd(), 0, contentenc.HeaderLen)
if err != nil {
if !syscallcompat.IsENOSPC(err) {
tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.qIno.Ino, err.Error())
}
return nil, err
}
}
// Actually write header
_, err = f.fd.WriteAt(buf, 0)
if err != nil {
return nil, err
}
return h.ID, err
}
// doRead - read "length" plaintext bytes from plaintext offset "off" and append
// to "dst".
// Arguments "length" and "off" do not have to be block-aligned.
//
// doRead reads the corresponding ciphertext blocks from disk, decrypts them and
// returns the requested part of the plaintext.
//
// Called by Read() for normal reading,
// by Write() and Truncate() via doWrite() for Read-Modify-Write.
func (f *File) doRead(dst []byte, off uint64, length uint64) ([]byte, syscall.Errno) {
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// Get the file ID, either from the open file table, or from disk.
var fileID []byte
f.fileTableEntry.IDLock.Lock()
if f.fileTableEntry.ID != nil {
// Use the cached value in the file table
fileID = f.fileTableEntry.ID
} else {
// Not cached, we have to read it from disk.
var err error
fileID, err = f.readFileID()
if err != nil {
f.fileTableEntry.IDLock.Unlock()
if err == io.EOF {
// Empty file
return nil, 0
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}
buf := make([]byte, 100)
n, _ := f.fd.ReadAt(buf, 0)
buf = buf[:n]
hexdump := hex.EncodeToString(buf)
tlog.Warn.Printf("doRead %d: corrupt header: %v\nFile hexdump (%d bytes): %s",
f.qIno.Ino, err, n, hexdump)
return nil, syscall.EIO
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}
// Save into the file table
f.fileTableEntry.ID = fileID
}
f.fileTableEntry.IDLock.Unlock()
if fileID == nil {
log.Panicf("fileID=%v", fileID)
}
// Read the backing ciphertext in one go
blocks := f.contentEnc.ExplodePlainRange(off, length)
alignedOffset, alignedLength := blocks[0].JointCiphertextRange(blocks)
skip := blocks[0].Skip
tlog.Debug.Printf("doRead: off=%d len=%d -> off=%d len=%d skip=%d\n",
off, length, alignedOffset, alignedLength, skip)
ciphertext := f.rootNode.contentEnc.CReqPool.Get()
ciphertext = ciphertext[:int(alignedLength)]
n, err := f.fd.ReadAt(ciphertext, int64(alignedOffset))
if err != nil && err != io.EOF {
tlog.Warn.Printf("read: ReadAt: %s", err.Error())
return nil, fs.ToErrno(err)
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}
// The ReadAt came back empty. We can skip all the decryption and return early.
if n == 0 {
f.rootNode.contentEnc.CReqPool.Put(ciphertext)
return dst, 0
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}
// Truncate ciphertext buffer down to actually read bytes
ciphertext = ciphertext[0:n]
firstBlockNo := blocks[0].BlockNo
tlog.Debug.Printf("ReadAt offset=%d bytes (%d blocks), want=%d, got=%d", alignedOffset, firstBlockNo, alignedLength, n)
// Decrypt it
plaintext, err := f.contentEnc.DecryptBlocks(ciphertext, firstBlockNo, fileID)
f.rootNode.contentEnc.CReqPool.Put(ciphertext)
if err != nil {
if f.rootNode.args.ForceDecode && err == stupidgcm.ErrAuth {
// We do not have the information which block was corrupt here anymore,
// but DecryptBlocks() has already logged it anyway.
tlog.Warn.Printf("doRead %d: off=%d len=%d: returning corrupt data due to forcedecode",
f.qIno.Ino, off, length)
} else {
curruptBlockNo := firstBlockNo + f.contentEnc.PlainOffToBlockNo(uint64(len(plaintext)))
tlog.Warn.Printf("doRead %d: corrupt block #%d: %v", f.qIno.Ino, curruptBlockNo, err)
return nil, syscall.EIO
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}
}
// Crop down to the relevant part
var out []byte
lenHave := len(plaintext)
lenWant := int(skip + length)
if lenHave > lenWant {
out = plaintext[skip:lenWant]
} else if lenHave > int(skip) {
out = plaintext[skip:lenHave]
}
// else: out stays empty, file was smaller than the requested offset
out = append(dst, out...)
f.rootNode.contentEnc.PReqPool.Put(plaintext)
return out, 0
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}
// Read - FUSE call
func (f *File) Read(ctx context.Context, buf []byte, off int64) (resultData fuse.ReadResult, errno syscall.Errno) {
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if len(buf) > fuse.MAX_KERNEL_WRITE {
// This would crash us due to our fixed-size buffer pool
tlog.Warn.Printf("Read: rejecting oversized request with EMSGSIZE, len=%d", len(buf))
return nil, syscall.EMSGSIZE
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}
f.fdLock.RLock()
defer f.fdLock.RUnlock()
f.fileTableEntry.ContentLock.RLock()
defer f.fileTableEntry.ContentLock.RUnlock()
tlog.Debug.Printf("ino%d: FUSE Read: offset=%d length=%d", f.qIno.Ino, off, len(buf))
if f.rootNode.args.SerializeReads {
serialize_reads.Wait(off, len(buf))
}
out, errno := f.doRead(buf[:0], uint64(off), uint64(len(buf)))
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if f.rootNode.args.SerializeReads {
serialize_reads.Done()
}
if errno != 0 {
return nil, errno
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}
tlog.Debug.Printf("ino%d: Read: errno=%d, returning %d bytes", f.qIno.Ino, errno, len(out))
return fuse.ReadResultData(out), errno
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}
// doWrite - encrypt "data" and write it to plaintext offset "off"
//
// Arguments do not have to be block-aligned, read-modify-write is
// performed internally as necessary
//
// Called by Write() for normal writing,
// and by Truncate() to rewrite the last file block.
//
// Empty writes do nothing and are allowed.
func (f *File) doWrite(data []byte, off int64) (uint32, syscall.Errno) {
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fileWasEmpty := false
// Get the file ID, create a new one if it does not exist yet.
var fileID []byte
// The caller has exclusively locked ContentLock, which blocks all other
// readers and writers. No need to take IDLock.
if f.fileTableEntry.ID != nil {
fileID = f.fileTableEntry.ID
} else {
// If the file ID is not cached, read it from disk
var err error
fileID, err = f.readFileID()
// Write a new file header if the file is empty
if err == io.EOF {
fileID, err = f.createHeader()
fileWasEmpty = true
}
if err != nil {
return 0, fs.ToErrno(err)
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}
f.fileTableEntry.ID = fileID
}
// Handle payload data
dataBuf := bytes.NewBuffer(data)
blocks := f.contentEnc.ExplodePlainRange(uint64(off), uint64(len(data)))
toEncrypt := make([][]byte, len(blocks))
for i, b := range blocks {
blockData := dataBuf.Next(int(b.Length))
// Incomplete block -> Read-Modify-Write
if b.IsPartial() {
// Read
oldData, errno := f.doRead(nil, b.BlockPlainOff(), f.contentEnc.PlainBS())
if errno != 0 {
tlog.Warn.Printf("ino%d fh%d: RMW read failed: errno=%d", f.qIno.Ino, f.intFd(), errno)
return 0, errno
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}
// Modify
blockData = f.contentEnc.MergeBlocks(oldData, blockData, int(b.Skip))
tlog.Debug.Printf("len(oldData)=%d len(blockData)=%d", len(oldData), len(blockData))
}
tlog.Debug.Printf("ino%d: Writing %d bytes to block #%d",
f.qIno.Ino, len(blockData), b.BlockNo)
// Write into the to-encrypt list
toEncrypt[i] = blockData
}
// Encrypt all blocks
ciphertext := f.contentEnc.EncryptBlocks(toEncrypt, blocks[0].BlockNo, f.fileTableEntry.ID)
// Preallocate so we cannot run out of space in the middle of the write.
// This prevents partially written (=corrupt) blocks.
var err error
cOff := int64(blocks[0].BlockCipherOff())
if !f.rootNode.args.NoPrealloc {
err = syscallcompat.EnospcPrealloc(f.intFd(), cOff, int64(len(ciphertext)))
if err != nil {
if !syscallcompat.IsENOSPC(err) {
tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %v", f.qIno.Ino, f.intFd(), err)
}
if fileWasEmpty {
// Kill the file header again
f.fileTableEntry.ID = nil
err2 := syscall.Ftruncate(f.intFd(), 0)
if err2 != nil {
tlog.Warn.Printf("ino%d fh%d: doWrite: rollback failed: %v", f.qIno.Ino, f.intFd(), err2)
}
}
return 0, fs.ToErrno(err)
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}
}
// Write
_, err = f.fd.WriteAt(ciphertext, cOff)
// Return memory to CReqPool
f.rootNode.contentEnc.CReqPool.Put(ciphertext)
if err != nil {
tlog.Warn.Printf("ino%d fh%d: doWrite: WriteAt off=%d len=%d failed: %v",
f.qIno.Ino, f.intFd(), cOff, len(ciphertext), err)
return 0, fs.ToErrno(err)
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}
return uint32(len(data)), 0
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}
// isConsecutiveWrite returns true if the current write
// directly (in time and space) follows the last write.
// This is an optimisation for streaming writes on NFS where a
// Stat() call is very expensive.
// The caller must "wlock.lock(f.devIno.ino)" otherwise this check would be racy.
func (f *File) isConsecutiveWrite(off int64) bool {
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opCount := openfiletable.WriteOpCount()
return opCount == f.lastOpCount+1 && off == f.lastWrittenOffset+1
}
// Write - FUSE call
//
// If the write creates a hole, pads the file to the next block boundary.
func (f *File) Write(ctx context.Context, data []byte, off int64) (uint32, syscall.Errno) {
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if len(data) > fuse.MAX_KERNEL_WRITE {
// This would crash us due to our fixed-size buffer pool
tlog.Warn.Printf("Write: rejecting oversized request with EMSGSIZE, len=%d", len(data))
return 0, syscall.EMSGSIZE
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}
f.fdLock.RLock()
defer f.fdLock.RUnlock()
if f.released {
// The file descriptor has been closed concurrently
tlog.Warn.Printf("ino%d fh%d: Write on released file", f.qIno.Ino, f.intFd())
return 0, syscall.EBADF
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}
f.fileTableEntry.ContentLock.Lock()
defer f.fileTableEntry.ContentLock.Unlock()
tlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.qIno.Ino, off, len(data))
// If the write creates a file hole, we have to zero-pad the last block.
// But if the write directly follows an earlier write, it cannot create a
// hole, and we can save one Stat() call.
if !f.isConsecutiveWrite(off) {
errno := f.writePadHole(off)
if errno != 0 {
return 0, errno
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}
}
n, errno := f.doWrite(data, off)
if errno != 0 {
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f.lastOpCount = openfiletable.WriteOpCount()
f.lastWrittenOffset = off + int64(len(data)) - 1
}
return n, errno
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}
// Release - FUSE call, close file
func (f *File) Release(ctx context.Context) syscall.Errno {
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f.fdLock.Lock()
if f.released {
log.Panicf("ino%d fh%d: double release", f.qIno.Ino, f.intFd())
}
f.released = true
openfiletable.Unregister(f.qIno)
err := f.fd.Close()
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f.fdLock.Unlock()
return fs.ToErrno(err)
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}
// Flush - FUSE call
func (f *File) Flush(ctx context.Context) syscall.Errno {
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f.fdLock.RLock()
defer f.fdLock.RUnlock()
err := syscallcompat.Flush(f.intFd())
return fs.ToErrno(err)
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}
// Fsync FUSE call
func (f *File) Fsync(ctx context.Context, flags uint32) (errno syscall.Errno) {
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f.fdLock.RLock()
defer f.fdLock.RUnlock()
return fs.ToErrno(syscall.Fsync(f.intFd()))
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}
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// Getattr FUSE call (like stat)
func (f *File) Getattr(ctx context.Context, a *fuse.AttrOut) syscall.Errno {
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f.fdLock.RLock()
defer f.fdLock.RUnlock()
tlog.Debug.Printf("file.GetAttr()")
st := syscall.Stat_t{}
err := syscall.Fstat(f.intFd(), &st)
if err != nil {
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return fs.ToErrno(err)
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}
f.rootNode.inoMap.TranslateStat(&st)
a.FromStat(&st)
a.Size = f.contentEnc.CipherSizeToPlainSize(a.Size)
if f.rootNode.args.ForceOwner != nil {
a.Owner = *f.rootNode.args.ForceOwner
}
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return 0
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}