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Comment by saagarjha | Hacker News Reader

> Good code requires discipline, doesn't it?

This is like the most clichéd way of saying “my code has security vulnerabilities” that there is. I have yet to see code that has remained secure solely on the “discipline” of programmers remembering to check things.

> The trick of checking that buffers are zeroed is purely a debugging tool, so it's okay if it doesn't work on some platforms.

Fair.

> And if you allocate with calloc(), the padding will be zeroed for you.

It might get unzeroed if you work with the memory.

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All code is full of vulnerabilites. If you say your code isn't, then I'm sure it is. I just do the best I can to keep the error rate as low as possible. But it's a rate, and it's never zero.

Also, it's not just about vulns in security-critical code. It's also about ordinary bugs. Why not be a little more careful? It won't hurt.

> It might get unzeroed if you work with the memory.

Maybe, but it isn't very common. I'm not sure when the C standard allows changing padding bytes, but in practice the compilers I've used don't seem to do it. And again, it's just a debugging aid, if it causes too much trouble on some platform, just turn it off.

It’s better to have automatic checks than rely on programmers being careful enough to remember to add them. For padding: this probably happens more on architectures that don’t do unaligned accesses very well.

> I have yet to see code that has remained secure solely on the “discipline” of programmers remembering to check things.

That's not what the parent comment said.

I’m not sure what it could have said after saying that programmers should have disciple after I mentioned that their thing required extra checks to work.

Parent said: "Good code requires discipline, doesn't it?"

You retort: "I have yet to see code that has remained secure solely on the “discipline” of programmers remembering to check things."

I think that is a dishonest misrepresentation of what the parent comment said, isn't it?

The “discipline” in this case (see the whole thread) is “have programmers remember to insert checks”, which has historically been a good way to have security holes crop up. So I’m not sure what was dishonest about it?

I don't think that's fair in this case because nulling out pointers isn't the first line of defense. If you forget to do it once, it's not going to cause a bug in and of itself. You can easily grep the code periodically to find any cases you missed.

Indeed, it shouldn't be a first line of defense (nulling + an assert seems reasonable, fwiw), and accessing a nulled out pointer is just as UB as any other UB. It's probably more likely to crash immediately in practice, but it's also easier for an optimizer to "see through", so you may get surprising optimizations if you get it wrong.

Honestly, unless you really cannot afford it time-budget wise, I would just ship everything with ASAN, UBSAN, etc. and deal with the crash reports.

Shipping code with Address Sanitizer enabled is generally not advisable; it has fairly high overhead. You should absolutely use it during testing, though!

That's why I added the "afford it" bit.

I think that's the misunderstanding, then, because to me it seemed to be a defensive coding practice (I think it was certainly presented as such in the top comment). My "you need extra checks" claim was mostly aimed at the additional things you add on to your code assuming that you are now zeroing out freed pointers, which I think can lead to dangerous situations where you may come to rely on this being done consistently when it's a manual process that is easy to forget.

Left unsaid due to the fact I was out doing groceries this morning when I posted that was that I don't think this is even a very good practice in general, as I explained in more detail in other comments here.

They argued that discipline is necessary, not sufficient, to produce good code. You represented the argument as: "discipline is sufficient for secure (good) code"

You took the original argument, changed it to be fallacious, and used it as a strawman. That's what was dishonest about it.

I appreciate you defending me, but I don't think he was trying to be dishonest.

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