libgocryptfs/internal/fusefrontend/fs.go
Jakob Unterwurzacher a355670ca2 fusefrontend: make Utimens symlink-safe
unix.UtimesNanoAt now also exists on Darwin, yay!
2019-01-01 16:24:25 +01:00

652 lines
21 KiB
Go

// Package fusefrontend interfaces directly with the go-fuse library.
package fusefrontend
// FUSE operations on paths
import (
"os"
"path/filepath"
"sync"
"syscall"
"time"
"golang.org/x/sys/unix"
"github.com/hanwen/go-fuse/fuse"
"github.com/hanwen/go-fuse/fuse/nodefs"
"github.com/hanwen/go-fuse/fuse/pathfs"
"github.com/rfjakob/gocryptfs/internal/contentenc"
"github.com/rfjakob/gocryptfs/internal/nametransform"
"github.com/rfjakob/gocryptfs/internal/serialize_reads"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
// FS implements the go-fuse virtual filesystem interface.
type FS struct {
pathfs.FileSystem // loopbackFileSystem, see go-fuse/fuse/pathfs/loopback.go
args Args // Stores configuration arguments
// dirIVLock: Lock()ed if any "gocryptfs.diriv" file is modified
// Readers must RLock() it to prevent them from seeing intermediate
// states
dirIVLock sync.RWMutex
// Filename encryption helper
nameTransform *nametransform.NameTransform
// Content encryption helper
contentEnc *contentenc.ContentEnc
// This lock is used by openWriteOnlyFile() to block concurrent opens while
// it relaxes the permissions on a file.
openWriteOnlyLock sync.RWMutex
// MitigatedCorruptions is used to report data corruption that is internally
// mitigated by ignoring the corrupt item. For example, when OpenDir() finds
// a corrupt filename, we still return the other valid filenames.
// The corruption is logged to syslog to inform the user, and in addition,
// the corrupt filename is logged to this channel via
// reportMitigatedCorruption().
// "gocryptfs -fsck" reads from the channel to also catch these transparently-
// mitigated corruptions.
MitigatedCorruptions chan string
// Track accesses to the filesystem so that we can know when to autounmount.
// An access is considered to have happened on every call to encryptPath,
// which is called as part of every filesystem operation.
// (This flag uses a uint32 so that it can be reset with CompareAndSwapUint32.)
AccessedSinceLastCheck uint32
}
var _ pathfs.FileSystem = &FS{} // Verify that interface is implemented.
// NewFS returns a new encrypted FUSE overlay filesystem.
func NewFS(args Args, c *contentenc.ContentEnc, n *nametransform.NameTransform) *FS {
if args.SerializeReads {
serialize_reads.InitSerializer()
}
if len(args.Exclude) > 0 {
tlog.Warn.Printf("Forward mode does not support -exclude")
}
return &FS{
FileSystem: pathfs.NewLoopbackFileSystem(args.Cipherdir),
args: args,
nameTransform: n,
contentEnc: c,
}
}
// GetAttr implements pathfs.Filesystem.
//
// GetAttr is symlink-safe through use of openBackingDir() and Fstatat().
func (fs *FS) GetAttr(relPath string, context *fuse.Context) (*fuse.Attr, fuse.Status) {
tlog.Debug.Printf("FS.GetAttr(%q)", relPath)
if fs.isFiltered(relPath) {
return nil, fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(relPath)
if err != nil {
return nil, fuse.ToStatus(err)
}
var st unix.Stat_t
err = syscallcompat.Fstatat(dirfd, cName, &st, unix.AT_SYMLINK_NOFOLLOW)
syscall.Close(dirfd)
if err != nil {
return nil, fuse.ToStatus(err)
}
a := &fuse.Attr{}
st2 := syscallcompat.Unix2syscall(st)
a.FromStat(&st2)
if a.IsRegular() {
a.Size = fs.contentEnc.CipherSizeToPlainSize(a.Size)
} else if a.IsSymlink() {
target, _ := fs.Readlink(relPath, context)
a.Size = uint64(len(target))
}
if fs.args.ForceOwner != nil {
a.Owner = *fs.args.ForceOwner
}
return a, fuse.OK
}
// mangleOpenFlags is used by Create() and Open() to convert the open flags the user
// wants to the flags we internally use to open the backing file.
// The returned flags always contain O_NOFOLLOW.
func (fs *FS) mangleOpenFlags(flags uint32) (newFlags int) {
newFlags = int(flags)
// Convert WRONLY to RDWR. We always need read access to do read-modify-write cycles.
if newFlags&os.O_WRONLY > 0 {
newFlags = newFlags ^ os.O_WRONLY | os.O_RDWR
}
// We also cannot open the file in append mode, we need to seek back for RMW
newFlags = newFlags &^ os.O_APPEND
// O_DIRECT accesses must be aligned in both offset and length. Due to our
// crypto header, alignment will be off, even if userspace makes aligned
// accesses. Running xfstests generic/013 on ext4 used to trigger lots of
// EINVAL errors due to missing alignment. Just fall back to buffered IO.
newFlags = newFlags &^ syscallcompat.O_DIRECT
// We always want O_NOFOLLOW to be safe against symlink races
newFlags |= syscall.O_NOFOLLOW
return newFlags
}
// Open - FUSE call. Open already-existing file.
//
// Symlink-safe through Openat().
func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile nodefs.File, status fuse.Status) {
if fs.isFiltered(path) {
return nil, fuse.EPERM
}
newFlags := fs.mangleOpenFlags(flags)
// Taking this lock makes sure we don't race openWriteOnlyFile()
fs.openWriteOnlyLock.RLock()
defer fs.openWriteOnlyLock.RUnlock()
// Symlink-safe open
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return nil, fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
fd, err := syscallcompat.Openat(dirfd, cName, newFlags, 0)
// Handle a few specific errors
if err != nil {
if err == syscall.EMFILE {
var lim syscall.Rlimit
syscall.Getrlimit(syscall.RLIMIT_NOFILE, &lim)
tlog.Warn.Printf("Open %q: too many open files. Current \"ulimit -n\": %d", cName, lim.Cur)
}
if err == syscall.EACCES && (int(flags)&os.O_WRONLY > 0) {
return fs.openWriteOnlyFile(dirfd, cName, newFlags)
}
return nil, fuse.ToStatus(err)
}
f := os.NewFile(uintptr(fd), cName)
return NewFile(f, fs)
}
// Due to RMW, we always need read permissions on the backing file. This is a
// problem if the file permissions do not allow reading (i.e. 0200 permissions).
// This function works around that problem by chmod'ing the file, obtaining a fd,
// and chmod'ing it back.
func (fs *FS) openWriteOnlyFile(dirfd int, cName string, newFlags int) (fuseFile nodefs.File, status fuse.Status) {
woFd, err := syscallcompat.Openat(dirfd, cName, syscall.O_WRONLY|syscall.O_NOFOLLOW, 0)
if err != nil {
return nil, fuse.ToStatus(err)
}
defer syscall.Close(woFd)
var st syscall.Stat_t
err = syscall.Fstat(woFd, &st)
if err != nil {
return nil, fuse.ToStatus(err)
}
// The cast to uint32 fixes a build failure on Darwin, where st.Mode is uint16.
perms := uint32(st.Mode & 0777)
// Verify that we don't have read permissions
if perms&0400 != 0 {
tlog.Warn.Printf("openWriteOnlyFile: unexpected permissions %#o, returning EPERM", perms)
return nil, fuse.ToStatus(syscall.EPERM)
}
// Upgrade the lock to block other Open()s and downgrade again on return
fs.openWriteOnlyLock.RUnlock()
fs.openWriteOnlyLock.Lock()
defer func() {
fs.openWriteOnlyLock.Unlock()
fs.openWriteOnlyLock.RLock()
}()
// Relax permissions and revert on return
syscall.Fchmod(woFd, perms|0400)
if err != nil {
tlog.Warn.Printf("openWriteOnlyFile: changing permissions failed: %v", err)
return nil, fuse.ToStatus(err)
}
defer func() {
err2 := syscall.Fchmod(woFd, perms)
if err2 != nil {
tlog.Warn.Printf("openWriteOnlyFile: reverting permissions failed: %v", err2)
}
}()
rwFd, err := syscallcompat.Openat(dirfd, cName, newFlags, 0)
if err != nil {
return nil, fuse.ToStatus(err)
}
f := os.NewFile(uintptr(rwFd), cName)
return NewFile(f, fs)
}
// Create - FUSE call. Creates a new file.
//
// Symlink-safe through the use of Openat().
func (fs *FS) Create(path string, flags uint32, mode uint32, context *fuse.Context) (nodefs.File, fuse.Status) {
if fs.isFiltered(path) {
return nil, fuse.EPERM
}
newFlags := fs.mangleOpenFlags(flags)
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return nil, fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
fd := -1
// Handle long file name
if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
// Create ".name"
err = fs.nameTransform.WriteLongNameAt(dirfd, cName, path)
if err != nil {
return nil, fuse.ToStatus(err)
}
// Create content
fd, err = syscallcompat.Openat(dirfd, cName, newFlags|os.O_CREATE|os.O_EXCL, mode)
if err != nil {
nametransform.DeleteLongNameAt(dirfd, cName)
return nil, fuse.ToStatus(err)
}
} else {
// Create content, normal (short) file name
fd, err = syscallcompat.Openat(dirfd, cName, newFlags|syscall.O_CREAT|syscall.O_EXCL, mode)
if err != nil {
return nil, fuse.ToStatus(err)
}
}
// Set owner
if fs.args.PreserveOwner {
err = syscall.Fchown(fd, int(context.Owner.Uid), int(context.Owner.Gid))
if err != nil {
tlog.Warn.Printf("Create: Fchown() failed: %v", err)
}
}
f := os.NewFile(uintptr(fd), cName)
return NewFile(f, fs)
}
// Chmod - FUSE call. Change permissons on "path".
//
// Symlink-safe through use of Fchmodat().
func (fs *FS) Chmod(path string, mode uint32, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(path) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
// os.Chmod goes through the "syscallMode" translation function that messes
// up the suid and sgid bits. So use a syscall directly.
err = syscallcompat.Fchmodat(dirfd, cName, mode, unix.AT_SYMLINK_NOFOLLOW)
return fuse.ToStatus(err)
}
// Chown - FUSE call. Change the owner of "path".
//
// Symlink-safe through use of Fchownat().
func (fs *FS) Chown(path string, uid uint32, gid uint32, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(path) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
code = fuse.ToStatus(syscallcompat.Fchownat(dirfd, cName, int(uid), int(gid), unix.AT_SYMLINK_NOFOLLOW))
if !code.Ok() {
return code
}
if !fs.args.PlaintextNames {
// When filename encryption is active, every directory contains
// a "gocryptfs.diriv" file. This file should also change the owner.
// Instead of checking if "cName" is a directory, we just blindly
// execute the chown on "cName/gocryptfs.diriv" and ignore errors.
dirIVPath := filepath.Join(cName, nametransform.DirIVFilename)
syscallcompat.Fchownat(dirfd, dirIVPath, int(uid), int(gid), unix.AT_SYMLINK_NOFOLLOW)
}
return fuse.OK
}
// Mknod - FUSE call. Create a device file.
//
// Symlink-safe through use of Mknodat().
func (fs *FS) Mknod(path string, mode uint32, dev uint32, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(path) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
// Create ".name" file to store long file name (except in PlaintextNames mode)
if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
err = fs.nameTransform.WriteLongNameAt(dirfd, cName, path)
if err != nil {
return fuse.ToStatus(err)
}
// Create "gocryptfs.longfile." device node
err = syscallcompat.Mknodat(dirfd, cName, mode, int(dev))
if err != nil {
nametransform.DeleteLongNameAt(dirfd, cName)
}
} else {
// Create regular device node
err = syscallcompat.Mknodat(dirfd, cName, mode, int(dev))
}
if err != nil {
return fuse.ToStatus(err)
}
// Set owner
if fs.args.PreserveOwner {
err = syscallcompat.Fchownat(dirfd, cName, int(context.Owner.Uid),
int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Mknod: Fchownat failed: %v", err)
}
}
return fuse.OK
}
// Truncate - FUSE call. Truncates a file.
//
// Support truncate(2) by opening the file and calling ftruncate(2)
// While the glibc "truncate" wrapper seems to always use ftruncate, fsstress from
// xfstests uses this a lot by calling "truncate64" directly.
//
// Symlink-safe by letting file.Truncate() do all the work.
func (fs *FS) Truncate(path string, offset uint64, context *fuse.Context) (code fuse.Status) {
file, code := fs.Open(path, uint32(os.O_RDWR), context)
if code != fuse.OK {
return code
}
code = file.Truncate(offset)
file.Release()
return code
}
// Utimens - FUSE call. Set the timestamps on file "path".
//
// Symlink-safe through UtimesNanoAt.
func (fs *FS) Utimens(path string, a *time.Time, m *time.Time, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(path) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
ts := make([]unix.Timespec, 2)
ts[0] = unix.Timespec(fuse.UtimeToTimespec(a))
ts[1] = unix.Timespec(fuse.UtimeToTimespec(m))
err = unix.UtimesNanoAt(dirfd, cName, ts, unix.AT_SYMLINK_NOFOLLOW)
return fuse.ToStatus(err)
}
// StatFs - FUSE call. Returns information about the filesystem.
//
// Symlink-safe because the passed path is ignored.
func (fs *FS) StatFs(path string) *fuse.StatfsOut {
return fs.FileSystem.StatFs("")
}
// decryptSymlinkTarget: "cData64" is base64-decoded and decrypted
// like file contents (GCM).
// The empty string decrypts to the empty string.
//
// This function does not do any I/O and is hence symlink-safe.
func (fs *FS) decryptSymlinkTarget(cData64 string) (string, error) {
if cData64 == "" {
return "", nil
}
cData, err := fs.nameTransform.B64.DecodeString(cData64)
if err != nil {
return "", err
}
data, err := fs.contentEnc.DecryptBlock([]byte(cData), 0, nil)
if err != nil {
return "", err
}
return string(data), nil
}
// Readlink - FUSE call.
//
// Symlink-safe through openBackingDir() + Readlinkat().
func (fs *FS) Readlink(relPath string, context *fuse.Context) (out string, status fuse.Status) {
dirfd, cName, err := fs.openBackingDir(relPath)
if err != nil {
return "", fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
cTarget, err := syscallcompat.Readlinkat(dirfd, cName)
if err != nil {
return "", fuse.ToStatus(err)
}
if fs.args.PlaintextNames {
return cTarget, fuse.OK
}
// Symlinks are encrypted like file contents (GCM) and base64-encoded
target, err := fs.decryptSymlinkTarget(cTarget)
if err != nil {
tlog.Warn.Printf("Readlink %q: decrypting target failed: %v", cName, err)
return "", fuse.EIO
}
return string(target), fuse.OK
}
// Unlink - FUSE call. Delete a file.
//
// Symlink-safe through use of Unlinkat().
func (fs *FS) Unlink(path string, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(path) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(path)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
// Delete content
err = syscallcompat.Unlinkat(dirfd, cName, 0)
if err != nil {
return fuse.ToStatus(err)
}
// Delete ".name" file
if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
err = nametransform.DeleteLongNameAt(dirfd, cName)
if err != nil {
tlog.Warn.Printf("Unlink: could not delete .name file: %v", err)
}
}
return fuse.ToStatus(err)
}
// encryptSymlinkTarget: "data" is encrypted like file contents (GCM)
// and base64-encoded.
// The empty string encrypts to the empty string.
//
// Symlink-safe because it does not do any I/O.
func (fs *FS) encryptSymlinkTarget(data string) (cData64 string) {
if data == "" {
return ""
}
cData := fs.contentEnc.EncryptBlock([]byte(data), 0, nil)
cData64 = fs.nameTransform.B64.EncodeToString(cData)
return cData64
}
// Symlink - FUSE call. Create a symlink.
//
// Symlink-safe through use of Symlinkat.
func (fs *FS) Symlink(target string, linkName string, context *fuse.Context) (code fuse.Status) {
tlog.Debug.Printf("Symlink(\"%s\", \"%s\")", target, linkName)
if fs.isFiltered(linkName) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(linkName)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(dirfd)
cTarget := target
if !fs.args.PlaintextNames {
// Symlinks are encrypted like file contents (GCM) and base64-encoded
cTarget = fs.encryptSymlinkTarget(target)
}
// Create ".name" file to store long file name (except in PlaintextNames mode)
if !fs.args.PlaintextNames && nametransform.IsLongContent(cName) {
err = fs.nameTransform.WriteLongNameAt(dirfd, cName, linkName)
if err != nil {
return fuse.ToStatus(err)
}
// Create "gocryptfs.longfile." symlink
err = syscallcompat.Symlinkat(cTarget, dirfd, cName)
if err != nil {
nametransform.DeleteLongNameAt(dirfd, cName)
}
} else {
// Create symlink
err = syscallcompat.Symlinkat(cTarget, dirfd, cName)
}
if err != nil {
return fuse.ToStatus(err)
}
// Set owner
if fs.args.PreserveOwner {
err = syscallcompat.Fchownat(dirfd, cName, int(context.Owner.Uid),
int(context.Owner.Gid), unix.AT_SYMLINK_NOFOLLOW)
if err != nil {
tlog.Warn.Printf("Symlink: Fchownat failed: %v", err)
}
}
return fuse.OK
}
// Rename - FUSE call.
//
// Symlink-safe through Renameat().
func (fs *FS) Rename(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(newPath) {
return fuse.EPERM
}
oldDirfd, oldCName, err := fs.openBackingDir(oldPath)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(oldDirfd)
newDirfd, newCName, err := fs.openBackingDir(newPath)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(newDirfd)
// The Rename may cause a directory to take the place of another directory.
// That directory may still be in the DirIV cache, clear it.
fs.nameTransform.DirIVCache.Clear()
// Easy case.
if fs.args.PlaintextNames {
return fuse.ToStatus(syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName))
}
// Long destination file name: create .name file
nameFileAlreadyThere := false
if nametransform.IsLongContent(newCName) {
err = fs.nameTransform.WriteLongNameAt(newDirfd, newCName, newPath)
// Failure to write the .name file is expected when the target path already
// exists. Since hashes are pretty unique, there is no need to modify the
// .name file in this case, and we ignore the error.
if err == syscall.EEXIST {
nameFileAlreadyThere = true
} else if err != nil {
return fuse.ToStatus(err)
}
}
// Actual rename
tlog.Debug.Printf("Renameat %d/%s -> %d/%s\n", oldDirfd, oldCName, newDirfd, newCName)
err = syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName)
if err == syscall.ENOTEMPTY || err == syscall.EEXIST {
// If an empty directory is overwritten we will always get an error as
// the "empty" directory will still contain gocryptfs.diriv.
// Interestingly, ext4 returns ENOTEMPTY while xfs returns EEXIST.
// We handle that by trying to fs.Rmdir() the target directory and trying
// again.
tlog.Debug.Printf("Rename: Handling ENOTEMPTY")
if fs.Rmdir(newPath, context) == fuse.OK {
err = syscallcompat.Renameat(oldDirfd, oldCName, newDirfd, newCName)
}
}
if err != nil {
if nametransform.IsLongContent(newCName) && nameFileAlreadyThere == false {
// Roll back .name creation unless the .name file was already there
nametransform.DeleteLongNameAt(newDirfd, newCName)
}
return fuse.ToStatus(err)
}
if nametransform.IsLongContent(oldCName) {
nametransform.DeleteLongNameAt(oldDirfd, oldCName)
}
return fuse.OK
}
// Link - FUSE call. Creates a hard link at "newPath" pointing to file
// "oldPath".
//
// Symlink-safe through use of Linkat().
func (fs *FS) Link(oldPath string, newPath string, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(newPath) {
return fuse.EPERM
}
oldDirFd, cOldName, err := fs.openBackingDir(oldPath)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(oldDirFd)
newDirFd, cNewName, err := fs.openBackingDir(newPath)
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(newDirFd)
// Handle long file name (except in PlaintextNames mode)
if !fs.args.PlaintextNames && nametransform.IsLongContent(cNewName) {
err = fs.nameTransform.WriteLongNameAt(newDirFd, cNewName, newPath)
if err != nil {
return fuse.ToStatus(err)
}
// Create "gocryptfs.longfile." link
err = syscallcompat.Linkat(oldDirFd, cOldName, newDirFd, cNewName, 0)
if err != nil {
nametransform.DeleteLongNameAt(newDirFd, cNewName)
}
} else {
// Create regular link
err = syscallcompat.Linkat(oldDirFd, cOldName, newDirFd, cNewName, 0)
}
return fuse.ToStatus(err)
}
// Access - FUSE call. Check if a file can be accessed in the specified mode(s)
// (read, write, execute).
//
// Symlink-safe through use of faccessat.
func (fs *FS) Access(relPath string, mode uint32, context *fuse.Context) (code fuse.Status) {
if fs.isFiltered(relPath) {
return fuse.EPERM
}
dirfd, cName, err := fs.openBackingDir(relPath)
if err != nil {
return fuse.ToStatus(err)
}
err = unix.Faccessat(dirfd, cName, mode, unix.AT_SYMLINK_NOFOLLOW)
return fuse.ToStatus(err)
}
// reportMitigatedCorruption is used to report a corruption that was transparently
// mitigated and did not return an error to the user. Pass the name of the corrupt
// item (filename for OpenDir(), xattr name for ListXAttr() etc).
// See the MitigatedCorruptions channel for more info.
func (fs *FS) reportMitigatedCorruption(item string) {
if fs.MitigatedCorruptions == nil {
return
}
select {
case fs.MitigatedCorruptions <- item:
case <-time.After(1 * time.Second):
tlog.Warn.Printf("BUG: reportCorruptItem: timeout")
//debug.PrintStack()
return
}
}