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libgocryptfs
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fusefrontend: xattr: fix operations on files without read permissions 

* listxattr is fixed via the /proc/self/fd trick
* setxattr,removexattr are fixed by opening the file O_WRONLY

Fixes https://github.com/rfjakob/gocryptfs/issues/308
This commit is contained in:
Jakob Unterwurzacher 2019-01-02 20:48:46 +01:00
parent d269c28d16
commit b214be5e3f
3 changed files with 82 additions and 51 deletions
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11
internal/fusefrontend/fs.go
View File

@ -160,6 +160,17 @@ func (fs *FS) Open(path string, flags uint32, context *fuse.Context) (fuseFile n
return NewFile(f, fs)
}
// openBackingFile opens the ciphertext file that backs relative plaintext
// path "relPath". Always adds O_NOFOLLOW to the flags.
func (fs *FS) openBackingFile(relPath string, flags int) (fd int, err error) {
dirfd, cName, err := fs.openBackingDir(relPath)
if err != nil {
return -1, err
}
defer syscall.Close(dirfd)
return syscallcompat.Openat(dirfd, cName, flags|syscall.O_NOFOLLOW, 0)
}
// 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,

88
internal/fusefrontend/xattr.go
View File

@ -2,6 +2,8 @@
package fusefrontend
import (
"fmt"
"runtime"
"strings"
"syscall"
@ -34,11 +36,12 @@ func (fs *FS) GetXAttr(relPath string, attr string, context *fuse.Context) ([]by
return nil, _EOPNOTSUPP
}
file, fd, status := fs.getFileFd(relPath, context)
if !status.Ok() {
return nil, status
// 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 file.Release()
defer syscall.Close(fd)
cAttr := fs.encryptXattrName(attr)
@ -66,17 +69,18 @@ func (fs *FS) SetXAttr(relPath string, attr string, data []byte, flags int, cont
return _EOPNOTSUPP
}
file, fd, status := fs.getFileFd(relPath, context)
if !status.Ok() {
return status
// O_NONBLOCK to not block on FIFOs.
fd, err := fs.openBackingFile(relPath, syscall.O_WRONLY|syscall.O_NONBLOCK)
if err != nil {
return fuse.ToStatus(err)
}
defer file.Release()
defer syscall.Close(fd)
flags = filterXattrSetFlags(flags)
cAttr := fs.encryptXattrName(attr)
cData := fs.encryptXattrValue(data)
err := unix.Fsetxattr(fd, cAttr, cData, flags)
err = unix.Fsetxattr(fd, cAttr, cData, flags)
if err != nil {
return fuse.ToStatus(err)
}
@ -94,14 +98,15 @@ func (fs *FS) RemoveXAttr(relPath string, attr string, context *fuse.Context) fu
return _EOPNOTSUPP
}
file, fd, status := fs.getFileFd(relPath, context)
if !status.Ok() {
return status
// O_NONBLOCK to not block on FIFOs.
fd, err := fs.openBackingFile(relPath, syscall.O_WRONLY|syscall.O_NONBLOCK)
if err != nil {
return fuse.ToStatus(err)
}
defer file.Release()
defer syscall.Close(fd)
cAttr := fs.encryptXattrName(attr)
err := unix.Fremovexattr(fd, cAttr)
err = unix.Fremovexattr(fd, cAttr)
if err != nil {
return fuse.ToStatus(err)
}
@ -115,19 +120,30 @@ func (fs *FS) ListXAttr(relPath string, context *fuse.Context) ([]string, fuse.S
if fs.isFiltered(relPath) {
return nil, fuse.EPERM
}
file, fd, status := fs.getFileFd(relPath, context)
// On a symlink, getFileFd fails with ELOOP. Let's pretend there
// can be no xattrs on symlinks, and always return an empty result.
if status == fuse.Status(syscall.ELOOP) {
return nil, fuse.OK
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_WRONLY|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 !status.Ok() {
return nil, status
}
defer file.Release()
cNames, err := syscallcompat.Flistxattr(fd)
if err != nil {
return nil, fuse.ToStatus(err)
}
@ -199,23 +215,3 @@ func (fs *FS) decryptXattrValue(cData []byte) (data []byte, err error) {
}
return fs.contentEnc.DecryptBlock([]byte(cData), 0, nil)
}
// getFileFd calls fs.Open() on relative plaintext path "relPath" and returns
// the resulting fusefrontend.*File along with the underlying fd. The caller
// MUST call file.Release() when done with the file. The O_NONBLOCK flag is
// used to not block on FIFOs.
//
// Used by xattrGet() and friends.
func (fs *FS) getFileFd(relPath string, context *fuse.Context) (*File, int, fuse.Status) {
fuseFile, status := fs.Open(relPath, syscall.O_RDONLY|syscall.O_NONBLOCK, context)
if !status.Ok() {
return nil, -1, status
}
file, ok := fuseFile.(*File)
if !ok {
tlog.Warn.Printf("BUG: xattrGet: cast to *File failed")
fuseFile.Release()
return nil, -1, fuse.EIO
}
return file, file.intFd(), fuse.OK
}

34
internal/syscallcompat/sys_common.go
View File

@ -64,7 +64,7 @@ func Fgetxattr(fd int, attr string) (val []byte, err error) {
// only happen on MacOS).
//
// See https://github.com/pkg/xattr for a smarter solution.
// TODO: be smarter?
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Fgetxattr(fd, attr, buf)
if err == syscall.ERANGE {
@ -84,11 +84,11 @@ func Fgetxattr(fd int, attr string) (val []byte, err error) {
return val, nil
}
// Flistxattr is a wrapper unix.Flistxattr that handles buffer sizing and
// Flistxattr is a wrapper for unix.Flistxattr that handles buffer sizing and
// parsing the returned blob to a string slice.
func Flistxattr(fd int) (attrs []string, err error) {
// See the buffer sizing comments in Fgetxattr.
// TODO: be smarter?
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Flistxattr(fd, buf)
if err == syscall.ERANGE {
@ -101,7 +101,31 @@ func Flistxattr(fd int) (attrs []string, err error) {
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
buf = buf[:sz]
attrs = parseListxattrBlob(buf[:sz])
return attrs, nil
}
// Llistxattr is a wrapper for unix.Llistxattr that handles buffer sizing and
// parsing the returned blob to a string slice.
func Llistxattr(path string) (attrs []string, err error) {
// TODO: smarter buffer sizing?
buf := make([]byte, XATTR_BUFSZ)
sz, err := unix.Llistxattr(path, buf)
if err == syscall.ERANGE {
// Do NOT return ERANGE - the user might retry ad inifinitum!
return nil, syscall.EOVERFLOW
}
if err != nil {
return nil, err
}
if sz >= XATTR_SIZE_MAX {
return nil, syscall.EOVERFLOW
}
attrs = parseListxattrBlob(buf[:sz])
return attrs, nil
}
func parseListxattrBlob(buf []byte) (attrs []string) {
parts := bytes.Split(buf, []byte{0})
for _, part := range parts {
if len(part) == 0 {
@ -110,5 +134,5 @@ func Flistxattr(fd int) (attrs []string, err error) {
}
attrs = append(attrs, string(part))
}
return attrs, nil
return attrs
}