lib: add "on"/"off" support to kstrtobool

Add support for "on" and "off" when converting to boolean.

Signed-off-by: Kees Cook <[e-mail]>
Cc: Amitkumar Karwar <[e-mail]>
Cc: Andy Shevchenko <[e-mail]>
Cc: Daniel Borkmann <[e-mail]>
Cc: Heiko Carstens <[e-mail]>
Cc: Joe Perches <[e-mail]>
Cc: Kalle Valo <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Nishant Sarmukadam <[e-mail]>
Cc: Rasmus Villemoes <[e-mail]>
Cc: Steve French <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

lib/kstrtox.c

···
  * @s: input string
  * @res: result
  *
- * This routine returns 0 iff the first character is one of 'Yy1Nn0'.
- * Otherwise it will return -EINVAL.  Value pointed to by res is
- * updated upon finding a match.
+ * This routine returns 0 iff the first character is one of 'Yy1Nn0', or
+ * [oO][NnFf] for "on" and "off". Otherwise it will return -EINVAL.  Value
+ * pointed to by res is updated upon finding a match.
  */
 int kstrtobool(const char *s, bool *res)
 {
···
 	case '0':
 		*res = false;
 		return 0;
+	case 'o':
+	case 'O':
+		switch (s[1]) {
+		case 'n':
+		case 'N':
+			*res = true;
+			return 0;
+		case 'f':
+		case 'F':
+			*res = false;
+			return 0;
+		default:
+			break;
+		}
 	default:
 		break;
 	}