Secure Programming in GNU/Linux Systems: Part I

LNXPhreak writes "A new article on OSWeekly.com discusses secure programming in GPU/Linux systems in terms of programming talent and requirements. Quote: "A "secure program" is an application that sits on a security boundary, taking input from a source that does not have the same access rights as the program. Such programs include application programs used as viewers of remote data, web applications (including CGI scripts), network servers, and setuid/setgid programs."

Comments

Unsafe Languages?

[(1 -sqrt(5))*(2**-1)]

In spite of myself, I went into TFA with cautious optimism; the author lost a lot of credibility by me, however, when he averred:

C is an unsafe language, and the standard C library string functions are unsafe.

I'd counterplead (to borrow a gun-canard): languages are not unsafe, but programmers are.

Re:Unsafe Languages?

[gowen]

Well that's strictly true, but you know what he's saying.
The string handling functions of the standard C library make it very easy to write unsafe code.

Similarly, a car with very bad brakes isn't intrinsically unsafe, as long as the cautious driver is prepared to take alternative precautions on ever bend. But if the driver makes an error (and everyone, yes, even you, will eventually make an error), he's going to end up wrapped around a tree.

Even though other cars aren't safe in the hands of a bad driver, given that you will make mistakes, you'll have far fewer horrific crashes in a car with ABS.

Re:Unsafe Languages?

[Anonymous Coward]

In spite of myself, I went into TFA with cautious optimism; the author lost a lot of credibility by me, however, when he averred:

        C is an unsafe language, and the standard C library string functions are unsafe.

I'd counterplead (to borrow a gun-canard): languages are not unsafe, but programmers are.

You are wrong. C, by design, does not enforce any type of boundary checking something that many other languages do. Other languages do enforce that and are therefore, by design, safer than C. Your cliché doesn't hold - it is the same as saying "Internet Explorer isn't unsafe, users are." Besides, the quote doesn't come from the author but from the hacker Aleph One which is one of the top security expers in the world.

Re:Unsafe Languages?

[slavemowgli]

He does have a point, though. It *is* possible to use the standard C library string functions in a safe manner, but it's difficult and error-prone - and if you make just one mistake, it might well be enough to open an exploitable hole in your program.

It's important to realise that programmers aren't perfect. "unsafe" programmers, as you call them, are not something you'll ever be able to get rid of; your best bet is thus to give them tools that make it as easy as possible to write safe code and that will mitigate the impact when things *do* go wrong - in other words, tools that will fail in a defined and safe manner.

One of the problems with C (actually, one of its strengths, too, of course, depending your point of view) is that it's really only optimised for speed, and a lot of compromises were and still are made there. Similarly, another problem is that C is intended as a very low-level language - a hardware-independent macro-assembler with automatic register allocation, if you will. This makes it very suitable for certain low-level tasks (like OS kernel programming), but it also creates problems when you move higher up in the level hierarchy, away from the bare metal.

C does have its place, but if you want to develop an application that's not closely tied to the hardware etc., C probably isn't as ideal a choice as you might think - and at the very least, if you *do* decide to use it after all, you should be aware of its weaknesses and pitfalls so you can avoid them.

It's just like with guns. Guns can be handled in a safe manner, but that doesn't mean you should give everyone a loaded and unlocked gun who's never touched one before in his life - chances are that accidents *will* happen. And while you can say that it's handler's fault, not the gun's, well... accidents still will happen. It's better to get off of one's high horse and try to minimise the number of actual incidents (and the severity of those incidents that do happen), since that's what counts in the end.

Re:Unsafe Languages?

[miyako]

I completely agree with you're point, and just thought I would pose a random sort of thought I had.
The biggest problem with C and C++ is that it's very easy for novice programmers to create insecure programs because, for the most part, they don't know how to properly work with pointers. Now days it seems to me that much fewer people learn C/C++ than used to just a few years ago. In highschool in my CS pretty much everyone who knew any programming knew C or C++. Back then, and that was only a few years ago mind, it seemed rare to me to know anyone who knew, e.g. perl or Java, and didn't know C or (more often) C++.
Now, this semester I graduate with a degree in Computer Information Systems, and of the 20 or 30 people I know off hand that are within a semester or two of me, I'm the only one who is competent with C++. There are a couple of other people who vaguely know it, and could probably recognize the syntax, but couldn't write anything useful in it.
At my school, the programming languages that are explicitly required are Java, VB.NET, COBOL, and just enough C# to do some stuff in ASP.NET- which is required for the web class. They teach a couple of assembly classes, and a couple of C++ classes that are required for the CET majors and offered as an elective to the CIS majors. I'm the *ONLY* person in the 4 years I've been at school I know who is a CIS major who took these classes.
So now, a lot of people who call themselves programmers are graduating and, quite literally, have no idea what a pointer is. So, this makes me wonder. Are C and C++ safer because most of the bad programmers are now working in "safe" languages like Java, or are they less safe because people don't learn about pointers early on?
Personally, I never understood why people have such trouble with understanding pointers, but then it may be because in highschool I was lucky enough to have an absolutely fantastic computer science teacher who instilled the basic ideas in us about how the compiler works and how variables work, and what memory addresses are, etc. from our first programming class.
Anyway, there wasn't much of a point to all that (it's 4:20am right now, and I should have been in bed 4 or 5 hours ago, so just be thankful that it's coherent (if indeed it is)) but maybe it'll stimulate discussion anyway.

Re:Unsafe Languages?

[UlfJack]

How good a programmer are you? Good? Very good? Excellent? Even Perfect?

No doubt you are not perfect, you are human after all. Now, I've never seen a Java programmer write code that could be exploited with a buffer overflow exploit. But I've seen countless buffer overflow bugs in C software. Just subscribe to one of the numerous security mailing lists.

Yes, you can write unsafe software in Java. No doubt about that. But a language where you cannot use the standard library (string functions!!!) for security related software is at best not well designed.

Re:Unsafe Languages?

[master_p]

Actually, you are wrong: a programming language is as unsafe as the most "unsafe" programmer of a project is. In other words, you may have a team of C experts that write the most secure C, but it only takes one minor error from a not-so-experienced programmer or from an experienced programmer in a bad day to bring down whole systems.

So although your argument seems correct on the surface, it actually is not true: a programming language shall enforce safety.

Re:Unsafe Languages?

[Anonymous Coward]

Anyone who's still writing C probably has enough experience to know the pitfalls.

Yeah, and I'm the Queen of England.

I still see plenty of C code that I wonder how the hell it was written by an experienced programmer, but it was.

Re:Unsafe Languages?

[try_anything]

Exactly. Article writer has no knowledge in the area.

Or perhaps you're missing the point.

The article writer isn't saying that a smart, conscientious C programmer can't copy strings correctly 98% of the time. He's saying it isn't good enough to meet that standard, and most languages do better. Even C++ allows you to simply write string s2 = s1.

To do the same thing in C, the programmer must know or check the length of s1, know or check the length of s2 (actually, know or check whether s2 points to any memory at all), possibly reallocate memory for s2, and copy exactly the right number of characters from s1 to s2. There are many possibilities for a typo or a lack of caffeine to open a security hole.

this problem of stupid/lazy programmer

No one denies that requiring several lines of finicky code to perform a simple operation separates the mental weenies from mental he-men. If your ego is the biggest thing on the line when you create software, by all means, keep using C for everything.

Clash of the Cliches ...

[Zero__Kelvin]

Actually, C is an unsafe language, and guns are dangerous, even in the right hands. The definition of "The Right Hands(tm)" is: "Someone who knows how intrinsically dangerous they are by nature."

While we are throwing cliches around, I will toss this one out there: "The right tool for the right job."

You wouldn't want to protect yourself from an attacker with a sponge, even though they are soft and fuzzy and safe. You wouldn't want to go deer hunting with a compiler. The problem is this: A gun in the hands of a person who doesn't understand why people think they are dangerous, is very dangerous!

C is not a safe language ... it is a powerful one. One can write secure code with C, just as one can shoot oneself in the foot with it. You significantly minimize the risk of shooting yourself in the foot when you take a course that helps you understand how and why the gun is dangerous, and the methods you can use to mitigate the risk.

Here is the problem, though: You don't need a C permit to write code using the C language." As a result, there are far too many people out there haphazardly swinging the barrel of their C compiler around thinking C saftey is a matter of pointers. You can be as careful as you want about where you point your gun when it is in your hands, but if you believe that gun safety begins and ends there, someone is more than likely going to get hurt. It is not enough to be careful where you point your C compilers barrel. You need to lock it up when you are not using it ....

Unsafe languages (and implementation details)

[joel.neely]

The use of unconstrained pointers and casting (don't forget that in C this includes arrays!), combined with allocation of local data in the same stack that contains state information (registers to be restored upon function return) is at the heart of a large portion (most?) of the common security vulnerabilities on PCs.

Some large-ish number of years ago I saw an article in which the author (don't recall the name offhand, sorry) asserted that raw pointers were the data equivalent of GOTOs. Both are potentially useful as under-the-hood implementation mechanisms, but entirely too easy to abuse for them to be exposed in a high-level-language.