sysfs: Only accept read/write permissions for file attributes

For sysfs file attributes, only read and write permissions make sense.
Mask provided attribute permissions accordingly and send a warning
to the console if invalid permission bits are set.

This patch is originally from Guenter [1] and includes the fixup
explained in the thread, that is printing permissions in octal format
and limiting the scope of attributes to SYSFS_PREALLOC | 0664.

[1] https://lkml.org/lkml/2015/1/19/599

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

fs/sysfs/group.c

@@ -55,6 +55,12 @@ static int create_files(struct kernfs_node *parent, struct kobject *kobj,
 				if (!mode)
 					continue;
 			}
+
+			WARN(mode & ~(SYSFS_PREALLOC | 0664),
+			     "Attribute %s: Invalid permissions 0%o\n",
+			     (*attr)->name, mode);
+
+			mode &= SYSFS_PREALLOC | 0664;
 			error = sysfs_add_file_mode_ns(parent, *attr, false,
 						       mode, NULL);
 			if (unlikely(error))