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// Package fusefrontend interfaces directly with the go-fuse library.
package fusefrontend
import (
"fmt"
"runtime"
"strings"
"syscall"
"golang.org/x/sys/unix"
"github.com/hanwen/go-fuse/fuse"
"github.com/rfjakob/gocryptfs/internal/syscallcompat"
"github.com/rfjakob/gocryptfs/internal/tlog"
)
const _EOPNOTSUPP = fuse.Status(syscall.EOPNOTSUPP)
// xattr names are encrypted like file names, but with a fixed IV.
// Padded with "_xx" for length 16.
var xattrNameIV = []byte("xattr_name_iv_xx")
// We store encrypted xattrs under this prefix plus the base64-encoded
// encrypted original name.
var xattrStorePrefix = "user.gocryptfs."
// GetXAttr - FUSE call. Reads the value of extended attribute "attr".
//
// This function is symlink-safe through Fgetxattr.
func (fs *FS) GetXAttr(relPath string, attr string, context *fuse.Context) ([]byte, fuse.Status) {
if fs.isFiltered(relPath) {
return nil, fuse.EPERM
}
if disallowedXAttrName(attr) {
return nil, _EOPNOTSUPP
}
// O_NONBLOCK to not block on FIFOs.
fd, err := fs.openBackingFile(relPath, syscall.O_RDONLY|syscall.O_NONBLOCK)
if err != nil {
return nil, fuse.ToStatus(err)
}
defer syscall.Close(fd)
cAttr := fs.encryptXattrName(attr)
cData, err := syscallcompat.Fgetxattr(fd, cAttr)
if err != nil {
return nil, fuse.ToStatus(err)
}
data, err := fs.decryptXattrValue(cData)
if err != nil {
tlog.Warn.Printf("GetXAttr: %v", err)
return nil, fuse.EIO
}
return data, fuse.OK
}
// SetXAttr - FUSE call. Set extended attribute.
//
// This function is symlink-safe through Fsetxattr.
func (fs *FS) SetXAttr(relPath string, attr string, data []byte, flags int, context *fuse.Context) fuse.Status {
if fs.isFiltered(relPath) {
return fuse.EPERM
}
if disallowedXAttrName(attr) {
return _EOPNOTSUPP
}
// O_NONBLOCK to not block on FIFOs.
fd, err := fs.openBackingFile(relPath, syscall.O_WRONLY|syscall.O_NONBLOCK)
// Directories cannot be opened read-write. Retry.
if err == syscall.EISDIR {
fd, err = fs.openBackingFile(relPath, syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NONBLOCK)
}
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(fd)
flags = filterXattrSetFlags(flags)
cAttr := fs.encryptXattrName(attr)
cData := fs.encryptXattrValue(data)
err = unix.Fsetxattr(fd, cAttr, cData, flags)
if err != nil {
return fuse.ToStatus(err)
}
return fuse.OK
}
// RemoveXAttr - FUSE call.
//
// This function is symlink-safe through Fremovexattr.
func (fs *FS) RemoveXAttr(relPath string, attr string, context *fuse.Context) fuse.Status {
if fs.isFiltered(relPath) {
return fuse.EPERM
}
if disallowedXAttrName(attr) {
return _EOPNOTSUPP
}
// O_NONBLOCK to not block on FIFOs.
fd, err := fs.openBackingFile(relPath, syscall.O_WRONLY|syscall.O_NONBLOCK)
// Directories cannot be opened read-write. Retry.
if err == syscall.EISDIR {
fd, err = fs.openBackingFile(relPath, syscall.O_RDONLY|syscall.O_DIRECTORY|syscall.O_NONBLOCK)
}
if err != nil {
return fuse.ToStatus(err)
}
defer syscall.Close(fd)
cAttr := fs.encryptXattrName(attr)
err = unix.Fremovexattr(fd, cAttr)
if err != nil {
return fuse.ToStatus(err)
}
return fuse.OK
}
// ListXAttr - FUSE call. Lists extended attributes on the file at "relPath".
//
// This function is symlink-safe through Flistxattr.
func (fs *FS) ListXAttr(relPath string, context *fuse.Context) ([]string, fuse.Status) {
if fs.isFiltered(relPath) {
return nil, fuse.EPERM
}
var cNames []string
var err error
if runtime.GOOS == "linux" {
dirfd, cName, err2 := fs.openBackingDir(relPath)
if err2 != nil {
return nil, fuse.ToStatus(err2)
}
defer syscall.Close(dirfd)
procPath := fmt.Sprintf("/proc/self/fd/%d/%s", dirfd, cName)
cNames, err = syscallcompat.Llistxattr(procPath)
} else {
// O_NONBLOCK to not block on FIFOs.
fd, err2 := fs.openBackingFile(relPath, syscall.O_RDONLY|syscall.O_NONBLOCK)
// On a symlink, openBackingFile fails with ELOOP. Let's pretend there
// can be no xattrs on symlinks, and always return an empty result.
if err2 == syscall.ELOOP {
return nil, fuse.OK
}
if err2 != nil {
return nil, fuse.ToStatus(err2)
}
defer syscall.Close(fd)
cNames, err = syscallcompat.Flistxattr(fd)
}
if err != nil {
return nil, fuse.ToStatus(err)
}
names := make([]string, 0, len(cNames))
for _, curName := range cNames {
if !strings.HasPrefix(curName, xattrStorePrefix) {
continue
}
name, err := fs.decryptXattrName(curName)
if err != nil {
tlog.Warn.Printf("ListXAttr: invalid xattr name %q: %v", curName, err)
fs.reportMitigatedCorruption(curName)
continue
}
names = append(names, name)
}
return names, fuse.OK
}
// encryptXattrName transforms "user.foo" to "user.gocryptfs.a5sAd4XAa47f5as6dAf"
func (fs *FS) encryptXattrName(attr string) (cAttr string) {
// xattr names are encrypted like file names, but with a fixed IV.
cAttr = xattrStorePrefix + fs.nameTransform.EncryptName(attr, xattrNameIV)
return cAttr
}
func (fs *FS) decryptXattrName(cAttr string) (attr string, err error) {
// Reject anything that does not start with "user.gocryptfs."
if !strings.HasPrefix(cAttr, xattrStorePrefix) {
return "", syscall.EINVAL
}
// Strip "user.gocryptfs." prefix
cAttr = cAttr[len(xattrStorePrefix):]
attr, err = fs.nameTransform.DecryptName(cAttr, xattrNameIV)
if err != nil {
return "", err
}
return attr, nil
}
// encryptXattrValue encrypts the xattr value "data".
// The data is encrypted like a file content block, but without binding it to
// a file location (block number and file id are set to zero).
// Special case: an empty value is encrypted to an empty value.
func (fs *FS) encryptXattrValue(data []byte) (cData []byte) {
if len(data) == 0 {
return []byte{}
}
return fs.contentEnc.EncryptBlock(data, 0, nil)
}
// decryptXattrValue decrypts the xattr value "cData".
func (fs *FS) decryptXattrValue(cData []byte) (data []byte, err error) {
if len(cData) == 0 {
return []byte{}, nil
}
data, err1 := fs.contentEnc.DecryptBlock([]byte(cData), 0, nil)
if err1 == nil {
return data, nil
}
// This backward compatibility is needed to support old
// file systems having xattr values base64-encoded.
cData, err2 := fs.nameTransform.B64.DecodeString(string(cData))
if err2 != nil {
// Looks like the value was not base64-encoded, but just corrupt.
// Return the original decryption error: err1
return nil, err1
}
return fs.contentEnc.DecryptBlock([]byte(cData), 0, nil)
}
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