dmz: cloned binary: set +x permissions when creating regular tmpfile

While we did set +x when "sealing" regular temporary files, the "is
executable" checks were done before then and would thus fail, causing
the fallback to not work properly.

So just set +x after we create the file. We already have a O_RDWR handle
open when we do the chmod so we won't get permission issues when writing
to the file.

Fixes: e089db3 ("dmz: add fallbacks to handle noexec for O_TMPFILE and mktemp()")

Signed-off-by: lifubang <[email protected]>

Author: lifubang

libcontainer/dmz/cloned_binary_linux.go

@@ -64,9 +64,6 @@ func Memfd(comment string) (*os.File, SealFunc, error) {
 }
 
 func sealFile(f **os.File) error {
-	if err := (*f).Chmod(0o511); err != nil {
-		return err
-	}
 	// When sealing an O_TMPFILE-style descriptor we need to
 	// re-open the path as O_PATH to clear the existing write
 	// handle we have.
@@ -108,6 +105,9 @@ func mktemp(dir string) (*os.File, SealFunc, error) {
 	if err := os.Remove(file.Name()); err != nil {
 		return nil, nil, fmt.Errorf("unlinking classic tmpfile: %w", err)
 	}
+	if err := file.Chmod(0o511); err != nil {
+		return nil, nil, fmt.Errorf("chmod classic tmpfile: %w", err)
+	}
 	var stat unix.Stat_t
 	if err := unix.Fstat(int(file.Fd()), &stat); err != nil {
 		return nil, nil, fmt.Errorf("cannot fstat classic tmpfile: %w", err)