go-sandbox/pkg/memfd/memfd.go
2019-09-14 22:52:33 -07:00

53 lines
1.4 KiB
Go

// +build linux
// Package memfd provides a wrapper to linux memfd
package memfd
import (
"fmt"
"io"
"os"
"golang.org/x/sys/unix"
)
const createFlag = unix.MFD_CLOEXEC | unix.MFD_ALLOW_SEALING
const roSeal = unix.F_SEAL_SEAL | unix.F_SEAL_SHRINK | unix.F_SEAL_GROW | unix.F_SEAL_WRITE
// New creates a new memfd, caller need to close the file
func New(name string) (*os.File, error) {
fd, err := unix.MemfdCreate(name, createFlag)
if err != nil {
return nil, fmt.Errorf("memfd: memfd_create failed %v", err)
}
file := os.NewFile(uintptr(fd), name)
if file == nil {
unix.Close(fd)
return nil, fmt.Errorf("memfd: MewFile failed")
}
return file, nil
}
// DupToMemfd reads content from reader to sealed (readonly) memfd for given name
func DupToMemfd(name string, reader io.Reader) (*os.File, error) {
file, err := New(name)
if err != nil {
return nil, fmt.Errorf("DupToMemfd: new memfd failed %v", err)
}
// linux syscall sendfile might be more efficient here if reader is a file
if _, err = io.Copy(file, reader); err != nil {
file.Close()
return nil, fmt.Errorf("DupToMemfd: memfd io copy failed(%v)", err)
}
// make memfd readonly
if _, err = unix.FcntlInt(file.Fd(), unix.F_ADD_SEALS, roSeal); err != nil {
file.Close()
return nil, fmt.Errorf("DupToMemfd: memfd seal failed(%v)", err)
}
if _, err := file.Seek(0, 0); err != nil {
file.Close()
return nil, fmt.Errorf("DupToMemfd: seek failed(%v)", err)
}
return file, nil
}