fix some file mode bits missing when doing mount syscall

Signed-off-by: lifubang <lifubang@acmcoder.com>

libcontainer/mount_linux.go

@@ -1,6 +1,7 @@
 package libcontainer
 
 import (
+	"io/fs"
 	"strconv"
 
 	"golang.org/x/sys/unix"
@@ -103,3 +104,20 @@ func unmount(target string, flags int) error {
 	}
 	return nil
 }
+
+// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
+// Copy from https://cs.opensource.google/go/go/+/refs/tags/go1.20.7:src/os/file_posix.go;l=61-75
+func syscallMode(i fs.FileMode) (o uint32) {
+	o |= uint32(i.Perm())
+	if i&fs.ModeSetuid != 0 {
+		o |= unix.S_ISUID
+	}
+	if i&fs.ModeSetgid != 0 {
+		o |= unix.S_ISGID
+	}
+	if i&fs.ModeSticky != 0 {
+		o |= unix.S_ISVTX
+	}
+	// No mapping for Go's ModeTemporary (plan9 only).
+	return
+}