setup_task.rb

require 'pty'
require 'fileutils'

def execmd cmd
	begin
		PTY.spawn(cmd) do |r, w, pid|
			begin
				r.each { |line| print line;}
			rescue Errno::EIO
			end
		end
	rescue PTY::ChildExited => e
		puts "bootstrapped!"
	end
end

def debootstrap ubuntu_version, challname
	cmd = "debootstrap #{ubuntu_version} #{challname}_chroot"
	execmd cmd
end

def add_user challname
	cmd = "chroot #{challname}_chroot /bin/bash -c \"useradd -m -s /bin/bash #{challname}\""
	execmd cmd
end

def copy_task challname, flag
	FileUtils.copy challname, "./#{challname}_chroot/home/#{challname}/#{challname}"
	FileUtils.copy flag, "./#{challname}_chroot/home/#{challname}/#{flag}"
end

def write_shell_script challname, port
	script = []
	script << "#!/bin/bash"
	script << "socat TCP-LISTEN:#{port},fork,reuseaddr,chroot=./#{challname}_chroot,su=nobody EXEC:\"/home/#{challname}/#{challname}\""
	File.open("#{challname}_runner.sh", 'w') {|f| f.write script.join("\n")}
	FileUtils.chmod "+x", "#{challname}_runner.sh"
end

if ARGV.length != 4
	puts "#{$0} ubuntu_version task_bin flag port"
end

ubuntu_version = ARGV[0]
challname = ARGV[1]
flag = ARGV[2]
port = ARGV[3]

debootstrap ubuntu_version, challname
add_user challname
copy_task challname, flag
write_shell_script challname, port