Yusuf's Security Engineering Blog

C-curity 101: Writing Secure Code in C

Date: 2024-08-23

Ah, C. The language that's been around longer than most of us have been alive. It's like that old, quirky uncle at family gatherings - powerful, a bit unpredictable, and if you're not careful, it might just blow up in your face. But fear not, brave coders! Today, we're diving into the wild world of writing secure code in C. Buckle up, it's going to be a bumpy ride!

1. Buffer Overflows: The OG of Security Vulnerabilities

Remember when you were a kid and tried to pour a gallon of milk into a pint glass? Yeah, buffer overflows are kind of like that, except instead of milk on the floor, you get exploited systems. Let's look at a classic example:

char buffer[10];
gets(buffer);  // Don't do this!

Using gets() is like giving your program a blank check. It'll keep reading input until it hits a newline, buffer size be damned! Instead, try this:

char buffer[10];
fgets(buffer, sizeof(buffer), stdin);  // Much better!

2. Integer Overflows: When Math Goes Rogue

Integers in C are like that friend who always says they're "five minutes away" - they have limits, even if they don't always show it. Check this out:

int i = INT_MAX;
i++;  // Oops, we've gone too far!

Suddenly, i is negative! To avoid this, always check for potential overflows:

if (i < INT_MAX) {
    i++;
} else {
    // Handle the error
}

3. Format String Vulnerabilities: The Sneaky Saboteur

Format string vulnerabilities are like those "Choose Your Own Adventure" books, except the adventure is system compromise. Consider this:

char *user_input = get_input();
printf(user_input);  // Danger, Will Robinson!

If user_input contains format specifiers like %s or %x, you're in for a bad time. Instead, do this:

printf("%s", user_input);  // Safe and sound

Conclusion: Stay Paranoid, My Friends

Writing secure C code is like being a character in a horror movie - always assume something's out to get you. Check your inputs, validate your assumptions, and never, ever trust user input. Remember, in the world of C, you're not just a programmer - you're a digital bodyguard, protecting your program from the big, bad world out there.

Now go forth and code securely! And remember, when in doubt, add another layer of bounds checking. Your future self (and your users) will thank you.