init: use *os.File for passed file descriptors

While it doesn't make much of a practical difference, it seems far more
reasonable to use os.NewFile to wrap all of our passed file descriptors
to make sure they're tracked by the Go runtime and that we don't
double-close them.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

libcontainer/standard_init_linux.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"os"
 	"os/exec"
-	"strconv"
 
 	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/opencontainers/selinux/go-selinux"
@@ -25,8 +24,8 @@ type linuxStandardInit struct {
 	consoleSocket *os.File
 	pidfdSocket   *os.File
 	parentPid     int
-	fifoFd        int
-	logFd         int
+	fifoFile      *os.File
+	logPipe       *os.File
 	dmzExe        *os.File
 	config        *initConfig
 }
@@ -244,11 +243,11 @@ func (l *linuxStandardInit) Init() error {
 
 	// Close the log pipe fd so the parent's ForwardLogs can exit.
 	logrus.Debugf("init: about to wait on exec fifo")
-	if err := unix.Close(l.logFd); err != nil {
-		return &os.PathError{Op: "close log pipe", Path: "fd " + strconv.Itoa(l.logFd), Err: err}
+	if err := l.logPipe.Close(); err != nil {
+		return fmt.Errorf("close log pipe: %w", err)
 	}
 
-	fifoPath, closer := utils.ProcThreadSelf("fd/" + strconv.Itoa(l.fifoFd))
+	fifoPath, closer := utils.ProcThreadSelfFd(l.fifoFile.Fd())
 	defer closer()
 
 	// Wait for the FIFO to be opened on the other side before exec-ing the
@@ -269,7 +268,7 @@ func (l *linuxStandardInit) Init() error {
 	// N.B. the core issue itself (passing dirfds to the host filesystem) has
 	// since been resolved.
 	// https://github.com/torvalds/linux/blob/v4.9/fs/exec.c#L1290-L1318
-	_ = unix.Close(l.fifoFd)
+	_ = l.fifoFile.Close()
 
 	s := l.config.SpecState
 	s.Pid = unix.Getpid()