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// Package fusefrontend interfaces directly with the go-fuse library.
package fusefrontend
// FUSE operations on paths
import (
"strings"
"syscall"
"github.com/hanwen/go-fuse/fuse"
"github.com/pkg/xattr"
"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 on Linux.
// Darwin does not have fgetxattr(2) nor /proc. How to implement this on Darwin
// in a symlink-safe way?
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
}
cAttr := fs.encryptXattrName(attr)
cData, status := fs.getXattr(relPath, cAttr, context)
if !status.Ok() {
return nil, status
}
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.
//
// TODO: Make symlink-safe. Currently blocked because the xattr package does
// not provide fsetxattr.
func (fs *FS) SetXAttr(path string, attr string, data []byte, flags int, context *fuse.Context) fuse.Status {
if fs.isFiltered(path) {
return fuse.EPERM
}
if disallowedXAttrName(attr) {
return _EOPNOTSUPP
}
flags = filterXattrSetFlags(flags)
cPath, err := fs.getBackingPath(path)
if err != nil {
return fuse.ToStatus(err)
}
cAttr := fs.encryptXattrName(attr)
cData := fs.encryptXattrValue(data)
return unpackXattrErr(xattr.LSetWithFlags(cPath, cAttr, cData, flags))
}
// RemoveXAttr - FUSE call.
//
// TODO: Make symlink-safe. Blocker: package xattr does not provide
// fremovexattr(2).
func (fs *FS) RemoveXAttr(path string, attr string, context *fuse.Context) fuse.Status {
if fs.isFiltered(path) {
return fuse.EPERM
}
if disallowedXAttrName(attr) {
return _EOPNOTSUPP
}
cPath, err := fs.getBackingPath(path)
if err != nil {
return fuse.ToStatus(err)
}
cAttr := fs.encryptXattrName(attr)
return unpackXattrErr(xattr.LRemove(cPath, cAttr))
}
// ListXAttr - FUSE call. Lists extended attributes on the file at "path".
//
// TODO: Make symlink-safe. Blocker: package xattr does not provide
// flistxattr(2).
func (fs *FS) ListXAttr(path string, context *fuse.Context) ([]string, fuse.Status) {
if fs.isFiltered(path) {
return nil, fuse.EPERM
}
cPath, err := fs.getBackingPath(path)
if err != nil {
return nil, fuse.ToStatus(err)
}
cNames, err := xattr.LList(cPath)
if err != nil {
return nil, unpackXattrErr(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)
}
// unpackXattrErr unpacks an error value that we got from xattr.LGet/LSet/etc
// and converts it to a fuse status.
func unpackXattrErr(err error) fuse.Status {
if err == nil {
return fuse.OK
}
err2, ok := err.(*xattr.Error)
if !ok {
tlog.Warn.Printf("unpackXattrErr: cannot unpack err=%v", err)
return fuse.EIO
}
return fuse.ToStatus(err2.Err)
}
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