libgocryptfs/internal/fusefrontend/file.go

406 lines
11 KiB
Go

package fusefrontend
// FUSE operations on file handles
import (
"bytes"
"fmt"
"io"
"log"
"os"
"sync"
"syscall"
"time"
"github.com/hanwen/go-fuse/fuse"
"github.com/hanwen/go-fuse/fuse/nodefs"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// File - based on loopbackFile in go-fuse/fuse/nodefs/files.go
type file struct {
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
// Was the file opened O_WRONLY?
writeOnly bool
// Content encryption helper
contentEnc *contentenc.ContentEnc
// Inode number
ino uint64
// File header
header *contentenc.FileHeader
// go-fuse nodefs.loopbackFile
loopbackFile nodefs.File
}
// NewFile returns a new go-fuse File instance.
func NewFile(fd *os.File, writeOnly bool, contentEnc *contentenc.ContentEnc) (nodefs.File, fuse.Status) {
var st syscall.Stat_t
err := syscall.Fstat(int(fd.Fd()), &st)
if err != nil {
tlog.Warn.Printf("NewFile: Fstat on fd %d failed: %v\n", fd.Fd(), err)
return nil, fuse.ToStatus(err)
}
wlock.register(st.Ino)
return &file{
fd: fd,
writeOnly: writeOnly,
contentEnc: contentEnc,
ino: st.Ino,
loopbackFile: nodefs.NewLoopbackFile(fd),
}, fuse.OK
}
// intFd - return the backing file descriptor as an integer. Used for debug
// messages.
func (f *file) intFd() int {
return int(f.fd.Fd())
}
func (f *file) InnerFile() nodefs.File {
return nil
}
func (f *file) SetInode(n *nodefs.Inode) {
}
// readHeader - load the file header from disk
//
// Returns io.EOF if the file is empty
func (f *file) readHeader() error {
buf := make([]byte, contentenc.HeaderLen)
_, err := f.fd.ReadAt(buf, 0)
if err != nil {
return err
}
h, err := contentenc.ParseHeader(buf)
if err != nil {
return err
}
f.header = h
return nil
}
// createHeader - create a new random header and write it to disk
func (f *file) createHeader() error {
h := contentenc.RandomHeader()
buf := h.Pack()
// Prevent partially written (=corrupt) header by preallocating the space beforehand
err := syscallcompat.EnospcPrealloc(int(f.fd.Fd()), 0, contentenc.HeaderLen)
if err != nil {
tlog.Warn.Printf("ino%d: createHeader: prealloc failed: %s\n", f.ino, err.Error())
return err
}
// Actually write header
_, err = f.fd.WriteAt(buf, 0)
if err != nil {
return err
}
f.header = h
return nil
}
func (f *file) String() string {
return fmt.Sprintf("cryptFile(%s)", f.fd.Name())
}
// doRead - returns "length" plaintext bytes from plaintext offset "off".
// 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() for Read-Modify-Write
func (f *file) doRead(off uint64, length uint64) ([]byte, fuse.Status) {
// Read file header
if f.header == nil {
err := f.readHeader()
if err == io.EOF {
return nil, fuse.OK
}
if err != nil {
return nil, fuse.ToStatus(err)
}
}
// 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("JointCiphertextRange(%d, %d) -> %d, %d, %d", off, length, alignedOffset, alignedLength, skip)
ciphertext := make([]byte, 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, fuse.ToStatus(err)
}
// 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, f.header.ID)
if err != nil {
curruptBlockNo := firstBlockNo + f.contentEnc.PlainOffToBlockNo(uint64(len(plaintext)))
cipherOff := f.contentEnc.BlockNoToCipherOff(curruptBlockNo)
plainOff := f.contentEnc.BlockNoToPlainOff(curruptBlockNo)
tlog.Warn.Printf("ino%d: doRead: corrupt block #%d (plainOff=%d, cipherOff=%d)",
f.ino, curruptBlockNo, plainOff, cipherOff)
return nil, fuse.EIO
}
// 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
return out, fuse.OK
}
// Read - FUSE call
func (f *file) Read(buf []byte, off int64) (resultData fuse.ReadResult, code fuse.Status) {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
tlog.Debug.Printf("ino%d: FUSE Read: offset=%d length=%d", f.ino, len(buf), off)
if f.writeOnly {
tlog.Warn.Printf("ino%d: Tried to read from write-only file", f.ino)
return nil, fuse.EBADF
}
out, status := f.doRead(uint64(off), uint64(len(buf)))
if status == fuse.EIO {
tlog.Warn.Printf("ino%d: Read failed with EIO, offset=%d, length=%d", f.ino, len(buf), off)
}
if status != fuse.OK {
return nil, status
}
tlog.Debug.Printf("ino%d: Read: status %v, returning %d bytes", f.ino, status, len(out))
return fuse.ReadResultData(out), status
}
// 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 neccessary
//
// 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, fuse.Status) {
// Read header from disk, create a new one if the file is empty
if f.header == nil {
err := f.readHeader()
if err == io.EOF {
err = f.createHeader()
}
if err != nil {
return 0, fuse.ToStatus(err)
}
}
var written uint32
status := fuse.OK
dataBuf := bytes.NewBuffer(data)
blocks := f.contentEnc.ExplodePlainRange(uint64(off), uint64(len(data)))
for _, b := range blocks {
blockData := dataBuf.Next(int(b.Length))
// Incomplete block -> Read-Modify-Write
if b.IsPartial() {
// Read
o := b.BlockPlainOff()
var oldData []byte
oldData, status = f.doRead(o, f.contentEnc.PlainBS())
if status != fuse.OK {
tlog.Warn.Printf("ino%d fh%d: RMW read failed: %s", f.ino, f.intFd(), status.String())
return written, status
}
// Modify
blockData = f.contentEnc.MergeBlocks(oldData, blockData, int(b.Skip))
tlog.Debug.Printf("len(oldData)=%d len(blockData)=%d", len(oldData), len(blockData))
}
// Encrypt
blockOffset := b.BlockCipherOff()
blockData = f.contentEnc.EncryptBlock(blockData, b.BlockNo, f.header.ID)
tlog.Debug.Printf("ino%d: Writing %d bytes to block #%d",
f.ino, uint64(len(blockData))-f.contentEnc.BlockOverhead(), b.BlockNo)
// Prevent partially written (=corrupt) blocks by preallocating the space beforehand
err := syscallcompat.EnospcPrealloc(int(f.fd.Fd()), int64(blockOffset), int64(len(blockData)))
if err != nil {
tlog.Warn.Printf("ino%d fh%d: doWrite: prealloc failed: %s", f.ino, f.intFd(), err.Error())
status = fuse.ToStatus(err)
break
}
// Write
_, err = f.fd.WriteAt(blockData, int64(blockOffset))
if err != nil {
tlog.Warn.Printf("doWrite: Write failed: %s", err.Error())
status = fuse.ToStatus(err)
break
}
written += uint32(b.Length)
}
return written, status
}
// Write - FUSE call
//
// If the write creates a hole, pads the file to the next block boundary.
func (f *file) Write(data []byte, off int64) (uint32, fuse.Status) {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
if f.released {
// The file descriptor has been closed concurrently, which also means
// the wlock has been freed. Exit here so we don't crash trying to access
// it.
tlog.Warn.Printf("ino%d fh%d: Write on released file", f.ino, f.intFd())
return 0, fuse.EBADF
}
wlock.lock(f.ino)
defer wlock.unlock(f.ino)
tlog.Debug.Printf("ino%d: FUSE Write: offset=%d length=%d", f.ino, off, len(data))
fi, err := f.fd.Stat()
if err != nil {
tlog.Warn.Printf("Write: Fstat failed: %v", err)
return 0, fuse.ToStatus(err)
}
plainSize := f.contentEnc.CipherSizeToPlainSize(uint64(fi.Size()))
if f.createsHole(plainSize, off) {
status := f.zeroPad(plainSize)
if status != fuse.OK {
tlog.Warn.Printf("zeroPad returned error %v", status)
return 0, status
}
}
return f.doWrite(data, off)
}
// Release - FUSE call, close file
func (f *file) Release() {
f.fdLock.Lock()
if f.released {
log.Panicf("ino%d fh%d: double release", f.ino, f.intFd())
}
f.fd.Close()
f.released = true
f.fdLock.Unlock()
wlock.unregister(f.ino)
}
// Flush - FUSE call
func (f *file) Flush() fuse.Status {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
// Since Flush() may be called for each dup'd fd, we don't
// want to really close the file, we just want to flush. This
// is achieved by closing a dup'd fd.
newFd, err := syscall.Dup(int(f.fd.Fd()))
if err != nil {
return fuse.ToStatus(err)
}
err = syscall.Close(newFd)
return fuse.ToStatus(err)
}
func (f *file) Fsync(flags int) (code fuse.Status) {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
return fuse.ToStatus(syscall.Fsync(int(f.fd.Fd())))
}
func (f *file) Chmod(mode uint32) fuse.Status {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
// os.File.Chmod goes through the "syscallMode" translation function that messes
// up the suid and sgid bits. So use syscall.Fchmod directly.
err := syscall.Fchmod(f.intFd(), mode)
return fuse.ToStatus(err)
}
func (f *file) Chown(uid uint32, gid uint32) fuse.Status {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
return fuse.ToStatus(f.fd.Chown(int(uid), int(gid)))
}
func (f *file) GetAttr(a *fuse.Attr) fuse.Status {
f.fdLock.RLock()
defer f.fdLock.RUnlock()
tlog.Debug.Printf("file.GetAttr()")
st := syscall.Stat_t{}
err := syscall.Fstat(int(f.fd.Fd()), &st)
if err != nil {
return fuse.ToStatus(err)
}
a.FromStat(&st)
a.Size = f.contentEnc.CipherSizeToPlainSize(a.Size)
return fuse.OK
}
// TODO drop this once https://github.com/hanwen/go-fuse/pull/131 is
// merged
const BrokenAtimeOmit = true
func (f *file) Utimens(a *time.Time, m *time.Time) fuse.Status {
if a == nil && BrokenAtimeOmit {
// Band-aid for a nil pointer crash, described in
// https://github.com/rfjakob/gocryptfs/issues/48
//
// TODO drop this once https://github.com/hanwen/go-fuse/pull/131 is
// merged
a = m
}
f.fdLock.RLock()
defer f.fdLock.RUnlock()
return f.loopbackFile.Utimens(a, m)
}