Daemon to randomize tcp_challenge_ack_limit to prevent side channel attacks CVE-2016-5696# chackd
chackd is a daemon which randomize each second the kernel parameter tcp_challenge_ack_limit to prevent side channel attacks
# Introduction
A shortly presented side-channel attack has given strong attention of the community [1] . For lots of servers or smartphone devices this attack considered dangerous for ipv4 connections. There is no doubt that the kernel will get fixed this issue in the next versions. However, some admins might not update the kernel due to specific reasons or just lazyness.
Adjusting the parameter to a very high value [2] will work fine. On the other side for server application it might result in an unecessary amount of traffic. To prevent this i have written the chackd program. It is able to get parametered to aim the solution presented in [1].
The chack daemon does this job very well and keeping it simple. An former concept of mine was looking for a loadable kernel module but i discarded this, because there is a powerful interface between user- and kernelspace called proc vfs. With proc files we are able to do the job with a simple daemon.
This is my first open-source project with a nice benifit for admins who want to secure agains challenge_ack_limit attacks and are not able to update their kernel. Just compile it and run it on your server.
I need help from the community to make this project "community standard".
# Files
1. *Makefile* - Makefile
2. *global.h* - Handle compiler options and define global variables
3. *main.c* - main function and your entry in chack-daemon
4. *init_daemon.h* - interface header for init_daemon.c
5. *init_daemon.c* - initialization of the daemon, just to make chackd a daemon process
6. *start_daemon.h*- interface header for start_daemon.c
7. *start_daemon.c*- main functionality with random-generator and proc-file Handling
8. *stop_daemon.h* - interface header for stop_daemon.c
9. *stop_daemon.c* - containing the signal handler for SIGUSR1 which is used to stopp the daemon
10. *test.sh* - simple check the current kernel parameter to show the daemon is working
11. *chackd.script.h* - start stop script of the daemon
# TODOs
Please look for TODOs inside the src files for some things i would like to work on. Feel free to branch in any way you want.
I would like to learn a lot from this project.
Makefile -
My wish for the Makefile is to make it a kind of standard with installation, kernel-release queries and so on.
start_daemon -
Any part of code which might cause the daemon to crash must be fixed
stop_daemon -
Any part of code which is not a kind of standard must be fixed
init_daemon -
Any part of code which might caus the daemon to crash must be fixed
main -
My intention is that main parameters are given as simple integer, currently it works well. However maybe there is a much better way of handling?
# Output
1 seconds intervall of "sysctl net.ipv4.tcp_challenge_ack_limit"
net.ipv4.tcp_challenge_ack_limit = 222
net.ipv4.tcp_challenge_ack_limit = 227
net.ipv4.tcp_challenge_ack_limit = 191
net.ipv4.tcp_challenge_ack_limit = 178
net.ipv4.tcp_challenge_ack_limit = 229
net.ipv4.tcp_challenge_ack_limit = 167
net.ipv4.tcp_challenge_ack_limit = 189
net.ipv4.tcp_challenge_ack_limit = 229
# Author
Bastian Pukallus, please mail to bastianpukallus@gmail.com
# Sources
[1] http://www.cs.ucr.edu/~zhiyunq/pub/sec16_TCP_pure_offpath.pdf
[2] https://www.mail-archive.com/debian-user@lists.debian.org/msg705042.html
[4.0K] /data/pocs/967d2a75ac94f01737c74a674dd4eb4dc58f0920
├── [ 34K] LICENSE
├── [ 232] Makefile
├── [3.4K] README.md
├── [4.0K] scripts
│ ├── [ 454] chackd.sh
│ └── [ 84] test.sh
└── [4.0K] src
├── [4.0K] include
│ ├── [ 785] global.h
│ ├── [ 190] init_daemon.h
│ ├── [ 145] start_daemon.h
│ └── [ 156] stop_daemon.h
├── [4.2K] init_daemon.c
├── [1.8K] main.c
├── [1.3K] start_daemon.c
└── [1.1K] stop_daemon.c
3 directories, 13 files