Service Docker Template

A Dockerfile template for preparing a Git-based CTF service.

Usage

You are free to modify the Dockerfile, but remember to not touch the base image, and to COPY the flag file into the /var/ctf directory. When you run ./setup.sh [service name] [port number], the script will automatically build a Docker image, and run your service in a container. The flag file can be filled with a random string. This file is used to prove the exploitability of an attack against your service.

Example

Below is an example that shows how you can run a simple echo server inside a Docker container.

1. Modify the Dockerfile as follows.

   FROM debian:latest
   
   # =========Install your package=========
   RUN apt-get update && apt-get install -y \
   make \
   gcc  \
   xinetd
   # ======================================
   
   RUN mkdir -p /var/ctf
   COPY flag /var/ctf/
   
   # ======Build and run your service======
   ADD /service /src
   COPY echo_service /etc/xinetd.d/
   
   RUN cd /src; make
   WORKDIR /src
   
   RUN echo "echo_service 4000/tcp" >> /etc/services
   
   RUN service xinetd restart
   ENTRYPOINT [ "xinetd", "-dontfork" ]

2. Create a xinetd configuration file as follows. We assume that the name of the config file is echo_service.

   service echo_service
   {
       flags = REUSE
       socket_type = stream
       wait = no
       user = root
       server = /src/echo
       disable = no
       port = 4000
   }

3. Write a simple echo server in C. We assume that you create a directory called service and put your program in the directory.

   /* service/echo.c */
   #include<stdio.h>
   #include<stdlib.h>
   #include<string.h>    //strlen
   #include<unistd.h>    //write
   
   int main()
   {
       char buf[256];
       while (1)
       {
           scanf("%s", buf);
   
           printf("%s\n", buf);
           fflush(stdout);
       }
       return 0;
   }

   # service/Makefile
   CC = gcc
   TARGET = echo
   
   all: echo
   
   echo:
       $(CC) $(TARGET).c -o $(TARGET)
   
   clean:
       rm $(TARGET)

4. Finally, you run ./setup.sh team1 4000 in order to run your echo service in a Docker container. The service will listen on port 4000.