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: NewFile failed for %v", name) } 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: %v", err) } // linux syscall sendfile might be more efficient here if reader is a file if _, err = file.ReadFrom(reader); err != nil { file.Close() return nil, fmt.Errorf("DupToMemfd: read from %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 %v", err) } if _, err := file.Seek(0, 0); err != nil { file.Close() return nil, fmt.Errorf("DupToMemfd: file seek %v", err) } return file, nil }