samples/kobject/: avoid world-writable sysfs files.

In line with practice for module parameters, we're adding a build-time
check that sysfs files aren't world-writable.

Cc: Greg Kroah-Hartman <greg@kroah.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

samples/kobject/kobject-example.c

@@ -40,8 +40,9 @@ static ssize_t foo_store(struct kobject *kobj, struct kobj_attribute *attr,
 	return count;
 }
 
+/* Sysfs attributes cannot be world-writable. */
 static struct kobj_attribute foo_attribute =
-	__ATTR(foo, 0666, foo_show, foo_store);
+	__ATTR(foo, 0664, foo_show, foo_store);
 
 /*
  * More complex function where we determine which variable is being accessed by
@@ -73,9 +74,9 @@ static ssize_t b_store(struct kobject *kobj, struct kobj_attribute *attr,
 }
 
 static struct kobj_attribute baz_attribute =
-	__ATTR(baz, 0666, b_show, b_store);
+	__ATTR(baz, 0664, b_show, b_store);
 static struct kobj_attribute bar_attribute =
-	__ATTR(bar, 0666, b_show, b_store);
+	__ATTR(bar, 0664, b_show, b_store);
 
 
 /*

samples/kobject/kset-example.c

@@ -124,8 +124,9 @@ static ssize_t foo_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
 	return count;
 }
 
+/* Sysfs attributes cannot be world-writable. */
 static struct foo_attribute foo_attribute =
-	__ATTR(foo, 0666, foo_show, foo_store);
+	__ATTR(foo, 0664, foo_show, foo_store);
 
 /*
  * More complex function where we determine which variable is being accessed by
@@ -157,9 +158,9 @@ static ssize_t b_store(struct foo_obj *foo_obj, struct foo_attribute *attr,
 }
 
 static struct foo_attribute baz_attribute =
-	__ATTR(baz, 0666, b_show, b_store);
+	__ATTR(baz, 0664, b_show, b_store);
 static struct foo_attribute bar_attribute =
-	__ATTR(bar, 0666, b_show, b_store);
+	__ATTR(bar, 0664, b_show, b_store);
 
 /*
  * Create a group of attributes so that we can create and destroy them all