fs: prepend statmount.mnt_opts string with security_sb_mnt_opts()

Currently these mount options aren't accessible via statmount().

The read handler for /proc/#/mountinfo calls security_sb_show_options()
to emit the security options after emitting superblock flag options, but
before calling sb->s_op->show_options.

Have statmount_mnt_opts() call security_sb_show_options() before
calling ->show_options.

Signed-off-by: Jeff Layton <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: jtlayton

fs/namespace.c

@@ -5036,6 +5036,10 @@ static int statmount_mnt_opts(struct kstatmount *s, struct seq_file *seq)
 	if (sb->s_op->show_options) {
 		size_t start = seq->count;
 
+		err = security_sb_show_options(seq, sb);
+		if (err)
+			return err;
+
 		err = sb->s_op->show_options(seq, mnt->mnt_root);
 		if (err)
 			return err;