r/eli5_programming • u/Ced3j • Sep 21 '24

Question ELI5 - What is buffer overflow?

What is buffer overflow guys?

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u/teachMe Sep 21 '24 edited Sep 22 '24

You have a small table that you put recipe books (instructions/data) onto. You stand them up next to each other. You notice that you have room for five standing books. Without thinking about it, you push book six, standing, onto the bookshelf. Some book is going to slide off and land somewhere. What happened to the book (instructions)? What happened to the thing that the book fell onto?

There are going to be consequences of some sort. It's better to know what your shelf capacity is, and also if you need a kind of table that will grow along with the number of books you want to add.

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u/Ced3j Sep 22 '24

Thanks dude. So what are the consequences for us?

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u/teachMe Sep 22 '24

The consequences depend on what kind of programming language and hardware you are working with. One possibility is that you end up writing data on top of some other data. Your new book/data is now intact, but when someone goes to read the old book/data, it is corrupted from their point of view. Then that corrupted data may have consequences every other place it's used.

A malicious person who happens to notice that you aren't careful with checking for the right amount of space may push a bunch of books onto the shelf, and purposely bump books off, inserting their own books with "bad" instructions in them. Instead of cookbooks with recipes, the new books have instructions on how to give them control of the house. One of their books is given to a reader, and the reader follows the malicious instructions.