sysfs: Use only return value from is_visible for the file mode

Up to now, is_visible can only be used to either remove visibility
of a file entirely or to add permissions, but not to reduce permissions.
This makes it impossible, for example, to use DEVICE_ATTR_RW to define
file attributes and reduce permissions to read-only.

This behavior is undesirable and unnecessarily complicates code which
needs to reduce permissions; instead of just returning the desired
permissions, it has to ensure that the permissions in the attribute
variable declaration only reflect the minimal permissions ever needed.

Change semantics of is_visible to only use the permissions returned
from it instead of oring the returned value with the hard-coded
permissions.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/sysfs/group.c

@@ -41,7 +41,7 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 
 	if (grp->attrs) {
 		for (i = 0, attr = grp->attrs; *attr && !error; i++, attr++) {
-			umode_t mode = 0;
+			umode_t mode = (*attr)->mode;
 
 			/*
 			 * In update mode, we're changing the permissions or
@@ -56,8 +56,7 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 					continue;
 			}
 			error = sysfs_add_file_mode_ns(parent, *attr, false,
-						       (*attr)->mode | mode,
-						       NULL);
+						       mode, NULL);
 			if (unlikely(error))
 				break;
 		}