Introduction

[Harsha Sharma]

On Tue, Dec 26, 2017 at 9:49 AM, Chen Jingpiao <chenjingpiao at gmail.com> wrote:
> On 12/25 10:26, Harsha Sharma wrote:
>> On Mon, Dec 25, 2017 at 6:51 PM, JingPiao Chen <chenjingpiao at gmail.com> wrote:
>> > On 12/25 06:12, Harsha Sharma wrote:
>> >> Hello everyone,
>> >
>> > Hi.
>> >
>> >> I'm Harsha Sharma, a sophomore student at Indian Institute of
>> >> Technology,  Roorkee, India.
>> >> I have knowledge of C, git, shell programming, kernel programming, gdb
>> >> and parsers and currently working as outreachy intern in Linux-kernel
>> >> (project nftables - Network filtration tool).
>> >> Strace is one of my favorite tools in linux and want to contribute to
>> >> the community.
>> >>  I have looked into the mail archives about getting started and
>> >> submitted two small patches. I have tried to understand the test
>> >> infrastructure and will like to add some tests or fix some of the
>> >> existing tests.
>> >> It'll be great if someone can suggest either some tests or any other
>> >> small bug-fix that I can work upon.
>> >> Thanks :)
>> >
>> > I think write netlink socket parser is suited for you. This is a GSoC 2016
>> > and 2017 project. The part of netfilter has not implemented yet.
>> > I working on it, but recent I am busy. If you are interested in it, please
>> > tell me.
>> >
>> Yes, definitely. I'm interested.
>> How should I start with the project ? (Any guidance will be
>> appreciated, meanwhile I'll try to go through your code in strace.)
>> Can you assign me a small task in the project ?
>> Thanks for your time. :')
>
> 300d9f1f: Further decode some attributes.
> 37dfe8c7: Implement a small protocol.
>
> You can read these commits to get some idea.

I'm unable to find the header file for kobject_uevent_types (like
rtnetlink.h and selinux_netlink.h in case of route and selinux ).
I'm approaching in the way similar to netlink_route and
netlink_selinux, is this correct ?

> I recommend you to decode libudev
> netlink header (struct udev_monitor_netlink_header).
>
> systemd/src/libudev/libudev-monitor.c: 76
> struct udev_monitor_netlink_header {
>         /* "libudev" prefix to distinguish libudev and kernel messages */
>         char prefix[8];
>         /*
>          * magic to protect against daemon <-> library message format mismatch
>          * used in the kernel from socket filter rules; needs to be stored in network order
>          */
>         unsigned int magic;
>         /* total length of header structure known to the sender */
>         unsigned int header_size;
>         /* properties string buffer */
>         unsigned int properties_off;
>         unsigned int properties_len;
>         /*
>          * hashes of primary device properties strings, to let libudev subscribers
>          * use in-kernel socket filters; values need to be stored in network order
>          */
>         unsigned int filter_subsystem_hash;
>         unsigned int filter_devtype_hash;
>         unsigned int filter_tag_bloom_hi;
>         unsigned int filter_tag_bloom_lo;
> };

./tests/netlink_kobject_uevent
sendto(3, "\0\1\2\3\4\5\6\7\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36\37",
32, MSG_DONTWAIT, NULL, 0) = -1 ECONNREFUSED (Connection refused)
sendto(3, "=\0\1\2\3\4\5\6\7\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36"...,
33, MSG_DONTWAIT, NULL, 0) = -1 ECONNREFUSED (Connection refused)
+++ exited with 0 +++

This string "\0\1\2\3\4\5\6\7\10\t\n\v\f\r\16\17\20\21\22\23\24\25\26\27\30\31\32\33\34\35\36\37"
 needs to be parsed as prefix, magic, header_size, properties_off,
properties_len, and more ( from struct udev_monitor_netlink_header).
Is this correct, just want to make sure that I'm approaching in right
direction ?
Thanks for your time.

Regards,
Harsha Sharma

> Netlink overview and its strace parsers:
> http://blog.saruta.eu/netlink_strace.html
>
>>
>> > More information:
>> >
>> > strace GSoC 2017 netlink socket parsers:
>> > https://ppiao.github.io/2017/08/22/strace-gsoc-2017-netlink-socket-parser.html
>> >
>> > My current work of netfilter parser:
>> > (Need to fix.)
>> > https://github.com/ppiao/strace
>> >
>
> --
> Chen Jingpiao
>
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