C89/99

Week 0x0.3

Announcements

  • Welcome to Computing Security
  • Action Items:
    • Enigma assignment

Homework

  • The first homework, “Enigma”, is ready after this class.
    • Due Monday, 14 Jul at midnight AOE
    • The infamous CS1 hw, now in a good language!
    • Mostly just get the toolchain working.

Today

  • Reintroduce the technologies
    • podman
    • vim
    • gcc
    • git

What is Podman?

  • Definition:
    • Platform to develop, ship, and run applications in isolated containers.
  • Benefits:
    • Portability, consistency across environments.
  • Editorializing:
    • Probably all code should be written in a container now that they exist.

In practice:

  • Windows only
    • Run wsl --install -d ubuntu command once
    • Run wsl to… enter wsl.
    • Run sudo apt update once
    • Run sudo apt upgrade once
    • Run sudo apt install podman
    • Use podman commands within WSL

In practice:

  • Mac only
    • Use podman desktop installer
    • Before using containers, run
      • podman machine start
      • If it didn’t work, may need to podman machine init
    • This may create a large file on your device
      • podman-machine-default-arm64.raw

In practice:

  • Podman works well without hacks on Linux
    • In fairness, the goal is have access to Linux anyways.
    • “Linux” search term shows ~100 jobs in Portland area
    • vs. 300:Python, 200:SQL, 100:Tableau, 200:R but the first is HVAC?
      • “HVAC/R Service Technician”

Podman

  • Podman solves the problem of writing code on one computer and running it another.
  • Simply specify a Podman image
    • a description of a imaginary computer
  • Podman will pretend to be that computer
  • We can run code “inside” Podman
    • Code in the container can’t tell it’s running inside Podman

Inside:

Images

  • Something we podman run -it is an image
    • It is a template that corresponds to many possible pretend computers
    • I think of them like object oriented class
    • They define something that could be

Containers

  • Each time we run said command, we have a different container
    • They have different file systems
    • Things we install don’t persist to future run instances.
    • I think of them like objects of a class
    • Like ‘1’ instead of ‘integer’
    • They are actually existing, running code.

Reuse

  • On Enigma, probably:
    • You opened a container.
    • You wrote some code in vim.
    • You compiled the code.
    • You ran the executable.
    • The executable deorbited a space station. /s
    • You closed the container and went to touch grass.

Attach

  • After touching grass, you
    • Came back to your PC
    • Had no graceful way to continue working on the code you wrote.
  • We solve this with attachment and detachment.

Servers

  • One of the most common ways to use containers is web dev.
  • They are easier to think of as:
    • A program, which
    • Hosts a webpage, which
    • Happens to need to run somewhere
      • That somewhere is a command line
      • Inside a pretend computer (container).

Sample

  • Docker maintains a sample container.
    • Podman is busy being free and open source.
  • Try this:

Breakdown

Command Explanation
podman do something with containers
run run a new container
-d detach - we’ll cover this next
-p This is port forward…
8080:80 80 is where websites usually live
8080 is where we went (:8080)
docker/... Name of an image

Ports

  • Ports aren’t the point, but
  • We should demystify.
  • Change 8080:80 to 8083:80

Two pages

  • Wait a minute…
    • There’s a webpage at 8080
    • There’s a webpage at 8083
    • They’re both from the same image.
    • They were started in the same command line (maybe)
  • That is two containers running concurrently.
    • Enter -d

Detach

  • When we run an image with the -d flag, it:
    • Created and ran as any other container, but
    • Runs “in the background”
      • Control does not change to container
      • It runs only its start command
      • It’s just like a remote web server.

Detach Dev

  • A perhaps nicer way to write code is
    • Create and detach a container
    • Leave it running or whatever
    • Use other podman commands to:
      • Pop into the container and e.g. vim
      • Transfer files in or out
      • Pause and restart to save resources.

ps

  • When fiddling about with containers…
    • It’s good to know who they are (names)
    • And what they do (command)
  • We can use podman ps
  • We see two servers (nginx) running

ps -a

  • You may also have many containers
  • podman ps -a to see old containers.
  • I had many such containers!
    • 4 GB worth, to be exact
  • Clean them all up with prune
  • System = containers, images, everything

exec -it

  • If there’s a detached container running
  • We can execute commands in that container.
  • You only have to specify enough of the name or id to be unique.
    • A server at 8080 beginning with id 7…
  • This returns hello, directly, without switching into the container.

/bin/sh

  • So far, I haven’t found a container without /bin/sh
  • The Linux command line, more or less
    • bash > sh, but sometimes only sh available
  • Get an interactive command prompt via
  • This is roughly the same as run -it
    • But on an existing container, not a base image

NOTE

  • In this example, a webserver is kept running.
  • By default, containers can stop running.
  • If a container isn’t under podman ps:
    • Find it with podman ps -a
    • Start it with podman start by name
  • Restarts the last container with vim:

vim

  • I’ve adopted a strong preference for just using vim
    • When I exit vim, I implicitly exit the container.
    • Feels better than typing exit, to me
  • So if we create an image with vim, we can
  • And go from there.

Today

  • Reintroduce the technologies
    • ✓ podman
    • vim
    • gcc
    • git

IDEs

  • At some point in time, code started being written in IDEs.
    • Integrated design environments.
    • To me, the first one was Eclipse (for Java)
  • That time was shortly before the 2008 financial crises
    • Don’t put in the course evals I blame Eclipse for the Great Recession

Why Vim fr tho?

  • It is a command at command line
  • It can be installed in containers

Containerfile

  • Here’s the “Containerfile” I’m using today:
Containerfile

Ubuntu

  • I use Ubuntu
Containerfile
  • It’s a bit annoying Alpine requires separately grabbing libc to print

apt

  • Ubuntu uses apt to manage packages, like gcc and vim
  • Images are notorious for having out-of-date package listings
Containerfile
  • This tells Ubuntu to look for the latest & greatest

&&

  • We use && to update and install at once
  • We use apt install to… install gcc from apt
Containerfile
  • This avoids a container updating, going to sleep, and packages falling out of date.
    • Apparently that actually happens on cloud, somehow

-y

  • We list whatever other packages we need and also…
  • -y as by default apt asks us if we’re sure
Containerfile
  • Without -y, apt will wait for us to type
    • We often use podman in scripts or commands where it gets stuck, so use -y

Usage

  • I usually enter a container via
  • Or often with a filename
  • From there I do a few things…

First window

  • It looks like this:

Insert mode

  • Press i to enter “insert mode”

Write some code

  • Type every letter perfectly on the first try.

:term

  • Open the vim terminal emulator
    • Press ESC
    • Type :term
    • Press ENTER
    • We’ll go step by step

Press ESC

  • Looks like this (mostly INSERT is gone)

Type “:term”

  • The colon : is meaningful in vim
#include <stdio.h>

int main(int argc, char **argv) {
        if (argc) {
                printf("%s\n", argv[1]);
        }
        return 0;
}                                                      
~                                                      
~                                                      
~                                                      
~                                                      
~                                                      
~                                                      
:term

Press ENTER

  • All kinds of colors could happen here too:
#





!sh [running]                        0,0-1          All
int main(int argc, char **argv) {
        if (argc) {                                                    
                printf("%s\n", argv[1]);                       
        }                                                      
        return 0;                                      
}                                                      
samp.c [+]                           8,1            Bot
:term

Use terminal

  • Let’s compile with gcc

Write file

  • We didn’t save samp.c, we will:
    • Use CTRL+w to change “window”
    • We will use any vim movement key, like j
      • j moves down one “thing”
      • usually line, now a window
    • We will use ESC + :w to write the file
    • Then return to terminal CTRL+w+k

That was a lot

  • Should look like this

Breathe

  • You are now all-powerful
    • You are not beholden to any operating system
    • Can work on cloud or anywhere with podman
    • If MS charges 10000 USD for VS Code tomorrow?
      • You are non-impacted
    • Everytime you do this you get faster

Verify Compilation

  • Use ls to list files, look for a.out

Run Executable

  • Use ./ prefix to use a.out as an executable

Segfault

  • In “samp.c” to fix off-by-one error, test

Today

  • ✓ Introduce the course
    • ✓ The C Programming Language
    • ✓ Cryptography + Cryptocurrency
  • Introduce the technologies
    • ✓ podman
    • ✓ vim
    • gcc
    • git

GCC

  • Developed for the C language to make an open source operating system in 1987.
  • Mainly around today for the C language to make an open source operating system (Linux)
  • (The C language was invented to write an operating system).
  • python is written in GCC C
C:\Users\cd-desk>podman run -it python
Python 3.13.1 (main, Dec  4 2024, 20:40:27) [GCC 12.2.0] on linux

Great freeware

  • Many legendary programs created using GCC:
    • HTTPD & NGINX, which serve a majority of webtraffic
    • Every major Linux and FreeBSD distribution
    • Major browsers like Firefox and Chromium
      • Firefox is on clang now but that’s new
    • GNU Bash and Coreutils, like cat, ls, rm
    • Bitcoin Core

Compilation

  • Like python or podman or vim, GCC is a command - gcc
  • gcc takes at least one argument: a filename, usually of a C file
  • GCC takes this C file and makes an executable
    • a program, sort of
  • Executables run as command with ./ prefix
    • This differs from python which runs a script without creating a corresponding program.

.py vs .c

flowchart LR
  A(Python) --> B[fname.py file]
  B --> C[python fname.py]
  C --> D{hello world}
  E(C) --> F[fname.c  file]
  F --> G[gcc fname.c -o ename]
  G --> H[./ename]
  H --> I{hello world}

  • You only have to compile once to have the executable forever.
  • Most programs are executables, not scripts.

Options

  • gcc has many options
    • -o specifies the name of the output file
    • -std specifies the C version (there’s a few)
    • -Wall -Wextra -Werror -Wpedantic set warnings - I use all 4
    • -w stop all warnings.
    • -O2 to compile more slowly to make faster code

C89/99

  • I prefer to write C89/99 compliant code
    • Later code is a bit too unclear for me
    • C89/99 have everything I need in a systems language
    • Most latter features I’d just switch to Python anyways
  • It tends to be easier to write compilers for C89 as well…

Podracing

  • Quickly pop back into our container.
    • Bookmark this page, save the text in a script, etc.
  • Pop open :term and run
  • My code runs fine. Let’s break it.

C++ //

  • Many C++ features have been adopted by C
  • Perhaps the most famous is C++ comments.
samp.c
#include <stdio.h>

int main(int argc, char **argv) {
        /* This is a C89 style comment */
        // This is a C++ style comment
        printf("hi\n");
        return 0;
}

std=c89

  • My vim window was tiny and I didn’t want to resize it
  • I opened a new terminal and tested
gcc samp.c --std=c89
user@DESKTOP-THMS2PJ:~/crypto/c89_99$ podman exec -it -l gcc samp.c --std=c89
samp.c: In function 'main':
samp.c:5:9: error: C++ style comments are not allowed in ISO C90
    5 |         // This is a C++ style comment
      |         ^
samp.c:5:9: note: (this will be reported only once per input file)
user@DESKTOP-THMS2PJ:~/crypto/c89_99$ podman exec -it -l gcc samp.c

-Wall etc

  • The other flags help “keep you honest”
    • If we wanted shortcuts, we’d use Python
    • We want to be percise [sic]
  • Try it:
gcc samp.c --std=c89 -Wall -Wextra -Werror -Wpedantic -O2

Whoops

  • You don’t want to find these problems latter.
  • Python needs -Wall for intro programming classes!

Benefits of C89

  • In C89, we must declare all variables at the beginning of functions.
  • Every “confused” Enigma I saw had massive variable name proliferation
  • Python lets you do this.
    • I argue this is Python preventing you from learning to program
  • The C89 language standard will protect you from writing bad code.

Expectation

cipher.c
#include <stdio.h>

char cipher(char c, int i) {
    return (c - 'A' + i) % 26 + 'A';
}

int main(int argc, char **argv) {
    int i;
    if (argc < 1) {
        return 1;
    }
    for (i = 0 ; argv[1][i]; i++) {
        argv[1][i] = cipher(argv[1][i], i);
    }
    printf("%s\n", argv[1]);
    return 0;
}

Reality

  • These flags prevent unused variables
  • These flags require variable declaration early.
    • We have to think, plan etc.

Example

  • Variable declared, not used.
int main(int argc, char **argv) {
    int i;
    /* if (argc < 1) {
        return 1;
    } */
    for (i = 0 ; argv[1][i]; i++) {
        argv[1][i] = cipher(argv[1][i], i);
    }
    printf("%s\n", argv[1]);
    return 0;
}
  • We can segmentation fault from an out-of-bounds error on argv.

Example

  • Variable declaration in function
int main(int argc, char **argv) {
    int i;
    for (i = 0 ; argv[1][i]; i++) {
        argv[1][i] = cipher(argv[1][i], i);
        int i++; 
    }
    printf("%s\n", argv[1]);
    return 0;
}
  • Prevents ill-formed variable changes.
    • Like .js const convention

Example

  • -Werror=char-subscripts
int main(int argc, char **argv) {
    char i;
    for (i = 0 ; argv[1][i]; i++) {
        argv[1][i] = cipher(argv[1][i], i);
    }
    printf("%s\n", argv[1]);
    return 0;
}
  • Ensures we can read strings of 255+ chars.

Example

  • Not technically wrong.
int main(int argc, char **argv) {
    char i;
    if (argc < 1) {
        return 1;
    }
    char *input_string = argv[1];
    for (i = 0 ; argv[1][i]; i++) {
        argv[1][i] = cipher(argv[1][i], i);
    }
    printf("%s\n", argv[1]);
    return 0;
}
  • But why?

Example

  • Actually wrong - output_string has no size.
int main(int argc, char **argv) {
    char i;
    if (argc < 1) {
        return 1;
    }
    char *output_string;
    for (i = 0 ; argv[1][i]; i++) {
        output_string[i] = cipher(argv[1][i], i);
    }
    printf("%s\n", argv[1]);
    return 0;
}
  • C89 catches this, others don’t.

Takeaway

  • As a second (or latter language)
  • Learn C by turning on compiler flags and writing code.
    • As a first language, use this little trick called “learn Python instead”
  • With practice, the correspondences will become obvious.
    • At that time, you will understand computing.

Practice to Perform

  • My take: learn C89 in class
    • Cultivate a disciplined coding practice
    • Work on older devices
    • Understand old code
    • Understand how computers work
  • Learn modern C via Stack Overflow
    • Understand how to code in practice

Today

  • Reintroduce the technologies
    • ✓ podman
    • ✓ vim
    • ✓ gcc
    • git

Git

  • Git was invented… to store the C language source code for an open source operating system (Linux)
  • It is de facto the only way in the universe to store code other than “on my HDD/SSD”
  • It is also a very good way to
      1. Store Containerfiles
      2. Steadily build a codebase

As a command

  • Git corresponds, like the others, to a command: git
    • It is common now to use other techniques, but the command remains extremely stable
  • Quoth GitHub, the first and greatest of the collaboration tools:
If you want a lot of control and flexibility, you can use the command line.

Henceforth

  • This week: Macros homework
  • This code will be used in the final project
  • Just like all the rest of the code we write this term
  • Store it on one big ole GitHub repo

Fun fact

  • Despite Big Command Line lobbying to get us to use git
  • There is no graceful way to set repositories to private at commandline
    • There’s a tactic doing API calls through the GitHub CLI
    • What are we even doing, open a browser
  • In 2024, browsers are decisively more secure than the commandline

Private

  • I recommend:
    • Pop in browser
    • Make a private github repo, like “crypto”
      • Add me as a collaborator
    • Name it “crypto”
    • Probably use a folder per week for hws
      • Maybe also labs, or just keep those local

GitHub x Podman

  • Over time, we’ll try to operationalize code better and better
  • Eventually, I plan to ask for a container in “ghcr”
    • GitHub Container Registry
  • In the meantime, I’d just keep a Containerfile at top level in your “crypto” repo.

Today

  • Reintroduce the technologies
    • ✓ podman
    • ✓ vim
    • ✓ gcc
    • ✓ git

Stinger

root@262ad65a08ba:/# vim build.sh
root@262ad65a08ba:/# ./build.sh
bash: ./build.sh: Permission denied
root@262ad65a08ba:/# chmod 777 build.sh
root@262ad65a08ba:/# ./build.sh
samp.c: In function 'main':
samp.c:5:9: error: C++ style comments are not allowed in ISO C90
    5 |         // This is a C++ style comment
      |         ^
samp.c:5:9: note: (this will be reported only once per input file)
samp.c:3:14: error: unused parameter 'argc' [-Werror=unused-parameter]
    3 | int main(int argc, char **argv) {
      |          ~~~~^~~~
samp.c:3:27: error: unused parameter 'argv' [-Werror=unused-parameter]
    3 | int main(int argc, char **argv) {
      |                    ~~~~~~~^~~~
cc1: all warnings being treated as errors
root@262ad65a08ba:/# cat build.sh
#!/bin/sh
gcc samp.c --std=c89 -Wall -Wextra -Werror -Wpedantic -O2 -o samp
root@262ad65a08ba:/#