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The Heartbleed Bug

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Re: The Heartbleed Bug

#231

Post by amalcon »

yaakov34 wrote: post #170
amalcon wrote: post #139

Earlier quoted context omitted.

Nothing in the standard prevents a C compiler + tightly coupled malloc implementation from implementing bounds checks. Out-of-bounds operations result in undefined behavior, and crashing the program is a valid response to undefined behavior. If your malloc implementation cooperates, you can even bounds-check pointer arithmetic without violating calling conventions. It's quite a shame that there isn't a compiler that…

Unrestricted pointer arithmetic is indeed incompatible with memory safety. You set a pointer to point to one structure, then you change it and it now points to another structure or array. The compiler doesn't know the semantics of your code, so how can it tell if you meant to do that? And malloc/memcpy is way too low to check this stuff. It only sees memory addresses; it has no idea what variables are in them. Tightl…

I'll assume the case you're concerned about is the one legitimately tricky case (where you have an array of structs that include arrays, and you perform arithmetic on a pointer into the inner array), because the other readings I'm coming up with necessarily invoke undefined behavior, either by running off the end of an allocation (what we're checking) or breaking strict aliasing (in which case false positives are OK). Depending on what you do with this pointer (e.g. passing it into a custom memcpy), the compiler may not be able to enforce runtime checks by itself.

This is where we do need some extra help, in the form of a library that holds state for the compiler so that we don't need to instrument our pointers. Nothing in the C standard prevents the compiler from doing this. The library you pass the pointer into may ignore this information, if it doesn't have the necessary instrumentation, but we at least get the capability.

Re: other languages, Rust I will grant. It's the only one of those that's compelling for C's use-cases (Java and C# are both entirely unusable for the best uses of C and C++).

Re: The Heartbleed Bug

#232

Post by AnthonyMouse »

halter73 wrote: post #28

> Recovery from this bug could benefit if the new version of the OpenSSL would both fix the bug and disable heartbeat temporarily until some future version... If only vulnerable versions of OpenSSL would continue to respond to the heartbeat for next few months then large scale coordinated response to reach owners of vulnerable services would become more feasible. This sounds risky to me. I'm afraid attackers would be…

In addition to that, it obviously disables the TLS heartbeat extension, which would break existing code that uses it.

Re: The Heartbleed Bug

#233

Post by nknighthb »

codygman wrote: post #223
pbsd wrote: post #191

Earlier quoted context omitted.

This sort of argument is becoming something of a fashion statement amongst some security people. It's not a strictly wrong argument: writing code in languages that make screwing up easy will invariably result in screwups. But it's a disingenuous one. It ignores the realities of systems. The reality is that there is currently no widely available memory-safe language that is usable for something like OpenSSL. .NET and…

I believe Haskell could be up to the job, but I heard that there were some difficulties in guarding against timing attacks. However those could have just been noise. I know that a functional (I believe and haha) operating system was made in Haskell. Aren't Operating Systems lower level than OpenSSL?

I look forward to reading the hilarious threads that will be spawned when you take to linux-kernel, freebsd-hackers, openbsd-misc, etc. and inform them they should be developing their kernels in Haskell.

Functional programming's unpopularity is not rooted in any real or imagined inability to write operating systems.

Re: The Heartbleed Bug

#234

Post by Gigablah »

whyleyc wrote: post #40
rguldener wrote: post #23

Earlier quoted context omitted.

I'd be surprised if heartbleed.com was still available in 2014

It was - registered 2 days ago by Marko Laakso from Codenomicon, the guys credited (by themselves it seems !) with finding the bug: http://www.networksolutions.com/whois/results.jsp?domain=hea...

They should probably get the guy who designed heartbleed.com to revamp their own website :)

Re: The Heartbleed Bug

#235

Post by userbinator »

jcalvinowens wrote: post #193
yaakov34 wrote: post #90

There was a discussion here a few years ago ( https://news.ycombinator.com/item?id=2686580 ) about memory vulnerabilities in C. Some people tried to argue back then that various protections offered by modern OSs and runtimes, such as address space randomization, and the availability of tools like Valgrind for finding memory access bugs, mitigates this. I really recommend re-reading that discussion. My opinion, then a…

> C and other languages without memory checks are unsuitable for writing secure code I vehemently disagree. Well-written C is very easy to audit. Much much moreso than languages like C# and Java, where something I could do with 200 lines in a single C source file requires 5 different classes in 5 different files. The problem with C is that a lot of people don't write it well. Have you looked at the OpenSSL source? It…

Agreed. Simple code is easy to understand and just as easy to find any bugs in. After looking at the heartbeat spec and the code, I can already see a simplification that, had it been written this way, would've likely avoided introducing this bug. Instead of allocating memory of a new length, how about just validating the existing message fields as per the spec:

> The total length of a HeartbeatMessage MUST NOT exceed 2^14 or max_fragment_length when negotiated as defined in [RFC6066].

> The padding_length MUST be at least 16.

> The sender of a HeartbeatMessage MUST use a random padding of at least 16 bytes.

> If the payload_length of a received HeartbeatMessage is too large, the received HeartbeatMessage MUST be discarded silently.

Then if it's all good, modify the buffer to change its type to heartbeat_response, fill the padding with new random bytes, and send this response. No need to copy the payload (which is where the bug was), no need to allocate more memory.

(Now I'm sure someone will try to find a flaw in this approach...)

Re: The Heartbleed Bug

#236

Post by rtpg »

pbsd wrote: post #227
rtpg wrote: post #211

Earlier quoted context omitted.

>Additionally, although the parsing portions of OpenSSL need not deal with the hardware directly, the crypto portions do. So your memory-safe language needs some first-class escape hatch to unsafe code. A few of them do have this, others not so much. For the other points there is some debate, but don't most serious languages have a C FFI?

OpenSSL and similar libraries spend most of their time processing short packets. For example, encrypting a few hundred bytes using AES these days should take only a few hundred CPU cycles. This means that the overhead of calling the crypto code should be minimal, preferably 0. This is in part what I meant by "first-class". Perhaps I should have written "zero-overhead" instead. I googled around just now for some bench…

those linked tests are extremely disingenuous, it only shows the fixed cost of FFIs.

Considering that in C the plusone call is 4 or so cycles, and the Java example is 5 times slower, that's only 20 or so cycles. If the function we're FFIing into is 400 cycles, that's only a 1% decrease in speed. I'm willing to pay that price if it means not having to wake up to everything being vulnerable every couple of months.

Re: The Heartbleed Bug

#237

Post by comex »

IgorPartola wrote: post #178
drv wrote: post #100

Earlier quoted context omitted.

From a quick reading of the TLS heartbeat RFC and the patched code, here's my understanding of the cause of the bug. TLS heartbeat consists of a request packet including a payload; the other side reads and sends a response containing the same payload (plus some other padding). In the code that handles TLS heartbeat requests, the payload size is read from the packet controlled by the attacker: n2s(p, payload); pl = p;…

Thanks for this. How is this reading arbitrary memory locations though? Isn't this always reading what is near the pl? As in, can you really scan the entire process's memory range this way or just a small subset where malloc (or the stack, whichever this is) places pl?

The latter, and AFAIK the buffer doesn't get reallocated on every connection, so it should be unlikely that any private keys actually get dumped. However, I could be missing a way to exploit it.

Re: The Heartbleed Bug

#238

Post by yaakov34 »

pbsd wrote: post #191
yaakov34 wrote: post #90

There was a discussion here a few years ago ( https://news.ycombinator.com/item?id=2686580 ) about memory vulnerabilities in C. Some people tried to argue back then that various protections offered by modern OSs and runtimes, such as address space randomization, and the availability of tools like Valgrind for finding memory access bugs, mitigates this. I really recommend re-reading that discussion. My opinion, then a…

This sort of argument is becoming something of a fashion statement amongst some security people. It's not a strictly wrong argument: writing code in languages that make screwing up easy will invariably result in screwups. But it's a disingenuous one. It ignores the realities of systems. The reality is that there is currently no widely available memory-safe language that is usable for something like OpenSSL. .NET and…

First, I do realize that rewriting the software stack from the ground up to have only managed code is a huge task. I do think that as an industry, we should set a goal of having at least one server implementation along these lines (where 'set a goal' may mean, say, grants or calls for proposals). Microsoft Research implemented an experimental OS like that, although it probably didn't have all the features a modern OS would need. I don't know if we need a new language, but we do need a huge rethink of the server architecture, and not just a piece-by-piece rewrite, which I think will founder on the interface issues that you mentioned.

Anyway, I am quite realistic about the prospect of my comment having that kind of effect on the industry - I don't suffer from delusions of grandeur. I was aiming the comment more at people who choose C/C++ for no good reason to write a user-level app; that app is nearly certain to have memory use errors, and if it has any network or remote interface, chances are they can be easily exploited. I'd like as many people as possible to understand that they can't expect to avoid such errors, any more than one of the most heavily audited pieces of software avoided them. We have had decades of exploits of this vulnerability, and yet most programmers are oblivious to it, or think only bad programmers are at risk. So just as tptacek goes around telling people not to write their own crypto, I go around telling people - with less authority and effectiveness, unfortunately - not to write C/C++ code unless they really need to.

As for the performance issues forcing OpenSSL to use C, well, we apparently exposed all our secrets in the pursuit of shaving off those cycles. I hope we are happy.

Re: The Heartbleed Bug

#239

Post by jcalvinowens »

rtpg wrote: post #221
jcalvinowens wrote: post #193

Earlier quoted context omitted.

> C and other languages without memory checks are unsuitable for writing secure code I vehemently disagree. Well-written C is very easy to audit. Much much moreso than languages like C# and Java, where something I could do with 200 lines in a single C source file requires 5 different classes in 5 different files. The problem with C is that a lot of people don't write it well. Have you looked at the OpenSSL source? It…

>The problem with C is that a lot of people don't write it well. There are languages that make it very very hard to write bad code. Haskell is a good example of where if your program type-checks, there's a high chance it's probably correct. C is a language that doesn't offer many advantages but offers very many disadvantages for its weak assurances. Things like the Haskell compiler show that you can get strong typing…

> There are languages that make it very very hard to write bad code. Haskell [...]

Sure, but how much slower is Haskell than an equivalent implementation in C? Some quick searching suggests numbers like 1000% slower... and no amount of security is worth a 1000% performance hit, let alone a vague "security mistakes are less likely this way" sort of security. Being secure is useless if your code is so slow that you have to run so many servers you don't make a profit.

Could the Haskell compiler be improved to the point that this isn't a problem? Maybe. Ultimately I think the problem is that Haskell code is very unlike object code, and that makes writing a good compiler very difficult. C is essentially portable assembler; translating it to object code is much more trivial.

> C is a language that doesn't offer many advantages but offers very many disadvantages for its weak assurances.

C offers simplicity. Sure, there are some quirks that are complex, but by and large it is one of the simplest languages in existence. Once you understand the syntax, you've essentially learned the language. Contrast that to Java and C#: you are essentially forced by the language to use this gigantic and complicated library all the time. You are also forced to write your code in pre-determined ways, using classes and other OOP abstractions. In C, I don't have to do that: I can write my code in whatever way I feel makes it maximally readable and performant.

C also offers flexibility: in C, I can make the computer do absolutely anything I want it to in exactly the way I want it to. Maybe I don't like 8-byte pointers on my 64-bit CPU, and I want to implement a linked list allocating nodes from a sparse memory-mapped pool with a known base address using 16-bit indexes which I add to the base to get the actual addresses when manipulating the list? That could be a big win depending on what you're doing, and (correct me if I'm wrong) there is no way to do that in Java or Haskell.

> there's no longer many excuses to run around with raw pointers except for legacy code.

If by "raw pointer" you mean haphazardly casting different things to (void * ) or (char * ) and doing arithmetic on them to access members of structures or something, I agree, 99.9% of the time you shouldn't do that.

Or are you talking about that "auto_ptr" and so-called "smart pointer" stuff in C++? In that case, your definition of "raw pointer" is every pointer I've ever defined in all the C source code I've ever written.

Pointers exist because that's the way computer hardware works: they will never go away. I'd rather deal with them directly, since it allows me to be clever sometimes and make things faster.

Re: The Heartbleed Bug

#240

Post by ehPReth »

sexmonad wrote: post #34
ams6110 wrote: post #30

Earlier quoted context omitted.

Writeup was too long. We need to know the short and sweet of what to fix.

Update to 1.0.1g, redo all crypto. That is, revoke certs and keys and regenerate.

Just a note to others: all crypto includes things like SSH keys, SSH host keys, and GPG keys. Anything in memory could have been read.
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