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hartkopp / can-isotp

Linux Kernel Module for ISO 15765-2:2016 CAN transport protocol PLEASE NOTE: This module is part of the mainline Linux kernel since version 5.10
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Backward compatibility for Linux 5.4+ versions in bind() #21

Closed pylessard closed 4 years ago

pylessard commented 4 years ago

Hi, I've been flagged an issue with my Python Iso-TP module (https://github.com/pylessard/python-can-isotp/issues/22) regarding a backward compatibility issue. After diving into it, I believe the issue is a conflict between Python and this module.

Apparently, opening an ISOTP socket with Python 3.7.6 and a can-isotp.ko built under Linux 5.4 doesn't work. I believe the problem arise from the addition of J1939 support that modified the size of the sockaddr_can structure (change acknowledges by yourself :) ).

Python create the address object for the user and deduce the length of the address object by using sizeof(*addr). If Python has been compiled with a headers of Linux 5.3, then the this value should be smaller than what one would get with Linux headers of Linux 5.4+.

This line here, checks for conflicts by validating the size of the address object. This verification will prevent the creation of ISO-TP socket if an older Python is used with a freshly compiled kernel module.

Is there a way to be backward compatible with this or should one make sure to keep his Python version aligned with his Kernel version?

Thanks!

hartkopp commented 4 years ago

Fixed in https://github.com/hartkopp/can-isotp/commit/fbed98a0b5de1bbb29479516cf9b4aeb8b52ec55 and https://github.com/hartkopp/can-isotp/commit/ced84cab120a1ddde2bd4561a18514707c8a6184 Thanks @pylessard !

pylessard commented 4 years ago

Very interesting, I wasn't aware of the existence of the offsetof macro! That makes a very nice fix. Thank you