For this task, you will need to pair up with one of your classmates: first,
each of you will write a simple C program that uses temporary files in an
insecure manner. When this is done, you will exploit the program written by
your colleague (and they will exploit yours). Finally, you will fixe the
problem in your program and have your colleague check that they can no longer
fool your program.

Before we begin, let's recap why temporary files are used:

 * useful for communication
 * and/or co-opting *external tools*
 * to a lesser degree to store large data
 * should be *removed* upon exit
 * usually created in a special, system-wide directory

# Vulnerable Program

In our case, we will be using `/tmp` for creating temporary files, since this
is the usual location on UNIX systems. The recommended way to create temporary
files is by using:


 * `mkstemp` to create and open a file
 * and `mkdtemp` to create a temporary directory

The details can be found in the respective manual pages. See:

    $ man mkstemp
    $ man mkdtemp

The simplest way to use the functions would be this:

    char fn[] = "/tmp/mytmpdir.XXXXXX";
    if ( !mkdtemp(fn) )
        return ERROR;
    /* ... */
    rmdir( fn );

However, we won't use those functions. Instead, we will go with the most
vulnerable thing: just use the username to create the temporary file. Write a
program that:

 * creates `/tmp/$LOGNAME.<fixed string>.tmp`
 * writes a message into this file
 * sleeps for 10 seconds
 * unlinks the file and terminates

Where $LOGNAME can be obtained in a C program by calling `getenv( "LOGNAME" )`.
You can use `asprintf` or `snprintf` to build the path.

# Exploit

When your paired up classmate is ready, run the program you wrote a few times
so they can observe its behaviour. Do not tell them anything about the name
that you chose for the temporary file. When they are satisfied they learned
enough, flip the roles.

The goal of each party is to read the message the other person's program
writes into the temporary file. When this is achieved, discuss what the
problem with the program was, fix the particular problem and try again.
Iterate until the program is secure.

When you are done with this task, move on to `preload.txt`.