[yourdetect]

From the comment section:

> To me the more salient questions are how long before (a) we get Rust in a core subsystem (thus making Rust truly _required_ instead of "optional unless you have hardware foo"), and (b) requiring Rust for _all_ new code.

Previously, the position was that C developers would not be forced to learn Rust.

And a few days ago a security vulnerability was found in the Rust Linux kernel code.

https://news.ycombinator.com/item?id=46309536

[AlotOfReading]

Where did anyone promise that the Rust bits will never have security issues? That CVE was a fantastic demonstration of just how much better the situation is in Rust code and I don't think there's a realistic argument that the experiment has been anything other than successful.

[uecker]

Was it? It seems more a fantastic demonstration how the same type of errors can also occur in Rust code.

[jrimbault]

In C this kind of issue is so common it wouldn't raise to the status of "CVE". People would just shrug and say "git gud".

[uecker]

This is certainly not true. But also arguments about "common" are completely misleading as long as there is many orders of magnitude more C code than Rust code.

[Certhas]

Maybe you haven't been paying much attention in this space. Google found empirically that error density in _unsafe_ Rust is still much lower than in C/C++. And only a small portion of code is unsafe. So per LOC Rust has orders of magnitudes fewer errors than C/C++ in real world Android development. And these are not small sample sizes. By now more code is being written in Rust than C++ at Google:

https://security.googleblog.com/2025/11/rust-in-android-move...

But don't take my word for it, you can hear about the benefits of Rust directly from GKH:

www.youtube.com/watch?v=HX0GH-YJbGw

There really isn't a good faith argument here. You can make mistakes in Rust? No one denies that. There is more C code so of course there are more mistakes in C code than in Rust? Complete red herring.

[uecker]

Hey, it was my point that the number of CVEs is red herring.

And no, I do not care or even believe what Google says. There are so many influencing factors.

[rtpg]

> And a few days ago a security vulnerability was found in the Rust Linux kernel code.

was it a security vulnerability? I'm pretty sure it was "just" a crash. Though maybe someone smarter than me could have turned that into something more.

I have no dog in this race, I really like the idea of Rust drivers but can very much understand retiscience at getting Rust to be handling more core parts of the kernel, just because Rust's value seems to pay off way more in higher level code where you have these invariants to maintain across large code paths (meanwhile writing a bunch of doubly-linked lists in unsafe Rust seems a bit like busy work, modulo the niceties Rust itself can give you)

[taneliv]

> was it a security vulnerability? I'm pretty sure it was "just" a crash.

It's a race condition resulting in memory corruption.[1][2] That corruption is shown to result in a crash. I don't think the implication is that it can result only in crashes, but this is not mentioned in the CVE.

Whether it is a vulnerability that an attacker can crash a system depends on your security model, I guess. In general it is not expected to happen and it stops other software from running, and can be controlled by entities or software who should not have that level of control, so it's considered a vulnerability.

[1] https://www.cve.org/CVERecord/?id=CVE-2025-68260 [2] https://lore.kernel.org/linux-cve-announce/2025121614-CVE-20...

[uecker]

It is entertaining to observe that how - after the bullshit and propaganda phase - Rust now slowly enters reality and the excuses for problems that did not magically disappear are now exactly the same as what we saw before from C programmers and which Rust proponents would have completely dismissed as unacceptable in the past ("this CVE is not exploitable", "all programmers make mistakes", "unwrap should never been used in production", "this really is an example how fantastic Rust is").

[simonask]

You have a wild amount of confirmation bias going on here, though.

Of course, this bug was in an `unsafe` block, which is exactly what you would expect given Rust's promises.

The promise of Rust was never that it is magical. The promise is that it is significantly easier to manage these types of problems.

[uecker]

There were certainly a lot of people running around claiming that "Rust eliminates the whole class of memory safety bugs." Of course, not everybody made such claims, but some did.

Whether it is "significantly easier" to manage these types of problems and at what cost remains to be seen.

I do not understand you comment about "confirmation bias" as did not make a quantitative prediction that could have bias.

[ivanbakel]

> There were certainly a lot of people running around claiming that "Rust eliminates the whole class of memory safety bugs."

Safe Rust does do this. Dropping into unsafe Rust is the prerogative of the programmer who wants to take on the burden of preventing bugs themselves. Part of the technique of Rust programming is minimising the unsafe part so memory errors are eliminated as much as possible.

If the kernel could be written in 100% safe Rust, then any memory error would be a compiler bug.

[UltraSane]

Safe Rust absolutely eliminates entire categories of bugs

[yourdetect]

> Of course, this bug was in an `unsafe` block, which is exactly what you would expect given Rust's promises.

The fix was outside of any Rust unsafe blocks. Which confused a lot of Rust developers on Reddit and elsewhere. Since fans of Rust have often repeated that only unsafe blocks have to be checked. Despite the Rustonomicon clearly spelling out that much more than the unsafe blocks might need to be checked in order to avoid UB.

[yencabulator]

The unsafe code relied on an assumption that was not true; the chosen fix was to make that assumption be true. Makes perfect sense to me.

[simonask]

Rust fanboys on Reddit are not contributing to the Linux kernel. What matters here is that Rust helps serious people deliver great code.

[dwattttt]

Is it any more or less amusimg, or perhaps tedious, watching the first Rust Linux kernel CVE be pounced on as evidence that "problems .. did not magically disappear"?

Does anyone involved in any of this work believe that a CVE in an unsafe block could not happen?

[chironjit]

In case anyone is keen for an explanation of the vulnerability, LowLevelTV has done a video on this:

https://youtu.be/dgPI7NfKCiQ?si=BVBQ0MxuDpsbCvOk

The TLDR is that this race condition happened with unsafe code, which was needed to interact with existing C code. This was not a vulnerability with Rust's model.

That said, you can absolutely use bad coding practices in Rust that can cause issues, even for a regular programmer.

Using unwrap without dealing with all return cases is one example. Of course, there is a right way to dealing with return methods, but it's up to the programmer to follow it

[bitwize]

As Rust's advantages over C continue to be proven, a shift in position to "suck it up, C devs" is to be expected.

[qingcharles]

Agree. As a dev I've had to pivot a dozen times in my career. If you're a dev you should be able to learn a new language fairly quickly, all the core elements are the same, just the vocabulary is a little different. Since nobody has "fixed" C to avoid these bugs, and we're not going to go as far as put Java or .Net in the kernel, then I think Rust is probably the best, most pragmatic solution we have right now.

[tormeh]

Eh, these are highly skilled individuals that just don't like learning a new thing, no matter how useful. That attitude is a problem to be managed, but these people deserve a certain amount of respect. Anyone saying "suck it" or similar should get a grip.

[kubb]

I think you’ve said the quiet part out loud by mentioning learning Rust.

The learning seems to be the only legitimate issue that people have. But they avoid mentioning it because it sounds intellectually lazy.

[simonask]

And it is intellectually lazy.

[thegrim000]

Well yeah, that's the strategy.

"You don't need to learn it or use it, we just want to do our own separate things with it over here"

.. some time later ..

"Oh yeah it's working good for us, we think it'd be useful to use it in these additional places, think about the benefits!"

.. some time later ..

"Now it's going to be core and required, either deal with it or get out"

They know they could never jump straight to the last step without revolt, so they shove their foot in the door with fake promises and smiles and then slowly over time force the door all the way open until they eventually get what they wanted from the beginning.

[dannersy]

There are lots of vulnerabilities in the C code, too. Should we remove C or do we accept that fact that no language is perfect since they are used by humans and continue to make improvements and use tools that help us along as time goes forward?

The cherry picking for this one Rust vulnerability to the ~150 C vulnerabilities is such a weird take that I can't help but think people have some weird hatred of Rust.

[yourdetect]

> Should we remove C or

Your post is curious, for the post I quoted basically argued for just that eventuality for all new code. Even as the new language introduces undefined behavior vulnerabilities.

The promises as stated previously, and the goal as stated by that lwn.net post now, are starkly different. And the poster did not even wait until the new language has proven its worth. And then a UB CVE comes by in the code in the new language.

What Linus wrote in the past:

https://www.phoronix.com/news/Torvalds-On-Rust-Maintainers

> So when you change the C interfaces, the Rust people will have to deal with the fallout, and will have to fix the Rust bindings. That's kind of the promise here: there's that "wall of protection" around C developers that don't want to deal with Rust issues in the promise that they don't have to deal with Rust.

That both you and that lwn.net poster writes these things, is extraordinarily weird and strange.

[dannersy]

But this sounds like hubris and user error, then, and not a language discussion at all?

[uecker]

I do not think it is weird. Every C bug was taken as clear evidence that we need to abandon C and switch to Rust. So the fact that there are also such bugs in Rust is - while obvious - also important to highlight. So it is not weird hatred against Rust, but hatred against bullshit. And considering that most of the code is C, your 150 C vulnerabilities is a meaningless number, so you still continue with this nonsense.

[johncolanduoni]

One C bug was not taken as clear evidence that we need to abandon C and switch to Rust. Hundreds of thousands of very similar bugs, over decades, in common code patterns were. I’ve never understood how other C or C++ developers could seriously question whether Rust solves any safety problems at all. Maybe the tradeoffs aren’t worth it for a particular use case, but how could you find it unimaginable that even just enforced bounds checks would catch lots of bugs that (normal, non-verified) C would miss? Do you doubt that Python code corrupts memory a lot less because you saw a CPython CVE once?

What language do you think Graydon Hoare was spending most of this time writing while he started working of Rust as a side project? Hint: it sure wasn’t Java. Rust is not the product of some developer who has only used 2 scripting languages and had to read the definition of stack-smashing off of Wikipedia showing those C developers how to live in the future. It’s not old enough for many of the developers working on it to have only ever used Rust. It’s mostly C and C++ developers trying to build a new option for solving their same problems.

[Xylakant]

> It’s mostly C and C++ developers trying to build a new option for solving their same problems.

I've observed that a lot of the folks I used to meet at ruby conferences have moved to Rust. No idea what led to this, but maybe it's just folks that were generally curious about new programming languages that moved to ruby when it became better known and that the same interest led to adopting Rust.

[johncolanduoni]

I worked on a Ruby codebase that moved to Rust - I think that part is mostly cargo-culting cool things in the news to be perfectly honest. There’s type safety advantages, but if Ruby’s performance envelope was even conceivably acceptable for your use-case there are likely better options. I strongly suspect a lot of the friction between Rust and only-C/C++ developers is the product of a bunch of people coming at Rust from higher level languages parroting lines about safety, and then looking at you blankly if you ask how it handles nested pointer indirection.

But I don’t think that applies to the people actually driving the language forward, just those talking a big game on HN/Reddit.

[uecker]

Giving the size and age of the C ecosystem, the number of bugs is not really a valid argument. We will see an increasing numbers with Rust as Rust is increasingly used. I also do not question that Rust solves some problems. It just solves them rather badly and at high cost while bringing new problems.

I looked at firefox code a decade ago, it was a complete complex nightmare mix of different languages. I can see that this motivated starting something new, but it was not a clean C code base (and not even C).

[johncolanduoni]

What number of CVEs is Rust kernel code allowed to have before we have good evidence it’s a categorical failure? Do you turn off KASLR for your Linux machines because there exist CVEs it doesn’t protect against?

[uecker]

As long as the kernel will be developed, there will be CVEs - even with Rust. So at what point the number is so high that we should drop Rust and move to formal verification? And even then, there will be CVEs... This whole argument is nonsense.

But I also do not agree that memory safety is of much higher importance than other issues. Memory safety is highly critical if you have a monopolistic walled garden spyware ecosystem - such as Android. Not that I do not want memory safety, but the people I know who got hacked, did not get hacked because of memory safety issue, but because of weak passwords or unpatched software. And at least the later problems gets harder with Rust...

[UltraSane]

The number of memory related bugs is absolutely a valid issue with C when the same bugs are impossible in Rust. The C memory model is a disaster when every computer is connected to the Internet.

[uecker]

You are saying the Rust bug in the kernel was impossible? How did it happen then? Come on guys.

[aw1621107]

> Every C bug was taken as clear evidence that we need to abandon C and switch to Rust.

I think more charitably it's every "simple" C bug that tends to provoke that reaction. Buffer overflows, use-after-frees, things for which mechanically-enforceable solutions have existed and been widespread for a while. I think more exotic bugs tend to produce more interesting discussions since the techniques for avoiding those bugs tend to be similarly exotic.

> So the fact that there are also such bugs in Rust

Similarly, I think you need to be careful about what exactly "such bugs" encompasses. This bug wasn't one of the above "simple" bugs IMHO, so I would guess an equivalent bug in C code would at least avoid the worst of the more strident calls you so dislike. Hard to say for sure, though, given our unfortunate lack of a time machine.

[uecker]

I agree with you that this is more nuanced and that I oversimplified this a bit in my comment.

[dannersy]

Okay, fair that since the majority of the codebase is C and that 150 vulnerabilities is probably negligible in comparison since we're talking about ratios, but if we're to be THAT nuanced then we also need to consider that code has been iterated upon for decades, so, I think the point is moot.

The claim has never, ever, been that Rust is bug free. The objective was to help reduce bugs, which is an outcome I've seen first hand in projects I work on. You still seem to speak in aggro terms, so it still feels like an emotional response to Rust.

[queejjd]

What features do you like the most in Rust? Are pattern matching and enums some of them?

[dannersy]

Ah, credibility attacks. Nice.

[bitwize]

Safe Rust eliminates some of the more common memory bugs in C. The bug under discussion was written in unsafe Rust—but even that doesn't obviate the huge advantages Rust has over C. Even unsafe Rust, for instance, has far fewer UB gotchas than C. And with Rust, you can isolate the tricky bits in 'unsafe' blocks and write higher-level logic in safe Rust, giving your code an extra layer of protection. C is 100% unsafe—"unsafe at any speed" as I like to say.

[uecker]

IMHO, "C is 100% unsafe" is a misleading way to look at it and the kind of exaggeration which I criticize. Also in C only specific language features are unsafe and not all code, and you can screen for these features and also isolate critical code in helper functions. Saying these features could appear everywhere is no difference from "unsafe" possibly appearing everywhere in Rust. I agree that "unsafe" is easier to find as a keyword, but I do not think this is a fundamental advantage, especially in projects where you have a lot of such "unsafe" blocks.

[Xylakant]

> Saying these features could appear everywhere is no difference from "unsafe" possibly appearing everywhere in Rust.

That's not true in practice: Unsafe code is clearly delineated and can be 100% correctly identified. In C, usage of dangerous features can occur at any point and is much harder to clearly separate.

[uecker]

First, if "unsafe" worked so well 100% time, why did we have this bug? (and many other) So this already obviously wrong statement.

Then yes, you can use dangerous features in C at any time, but obviously you can also use "unsafe" at any time. The only difference is that "unsafe" is clearer to recognize. But how much this is worth is unclear. First, if you do not invalidly reduce the discussion to only memory safety, you need to review all other code anyway! But even then, it is also not true that only the code marked with "unsafe" is relevant. This is major myth. The "unsafe" code can cause UB outside "unsafe" and logic bugs outside "unsafe" can cause bugs unsafe. This does not perfectly decouple if you Rust repeat this nonsense over and over again.

Don't get me wrong, I think the unsafe keyword is good idea. But the magical powers Rust fans attribute to it and the "SAFETY" comment they put next to it tells me they are a bit delusional.

[wmanley]

> in C only specific language features are unsafe and not all code

Using rust's definition of unsafe which is roughly "can cause undefined behaviour" then it seems to me isolating use of these features isn't possible. What is C without:

* Dereferencing pointers * Array access * Incrementing signed integers

You can do all of the above without invoking UB, but you can't separate the features in C that can cause UB from the ones that can't.

[uecker]

The first misunderstanding is that safety is a property of the language or not. Rust marketing convinced many people that this is so, but C can be safe or unsafe. Fil-C shows that even all of C can be memory safe (but at a substantial cost in performance). But even just with GCC and Clang, array access and signed integer can be made safe with a compiler flag, and a violation then traps and this is similar to a Rust panic. The cases which can not be dealt with easily are pointer arithmetic, unions, and free and concurrently related issues. And it is very well possible to isolate and review all of these. This will not find all bugs, but neither does this work perfectly for Rust "unsafe" as this bug (and many others) nicely illustrates.

[noosphr]

The safest computer is a rock.

The point is that when you start using rust in the real world to get real work done a lot of the promises that were made about safety have to be dropped because you need to boot your computer before the heat death of the universe. The result will be that we end up with something about as safe as C is currently - because CPUs are fundamentally unsafe and we need them to work somehow.

Rust is from the universe in which micro kernels weren't a dead end and we could avoid all the drivers being written in C.

[josephg]

> when you start using rust in the real world to get real work done a lot of the promises that were made about safety have to be dropped because you need to boot your computer before the heat death of the universe.

Safe rust isn't slow like Python, Go or Fil-C. It gets compiled to normal native code just like C and C++. It generally runs just as fast as C. At least, almost all the time. Arrays have runtime bounds checks. And ... thats about it.

> The result will be that we end up with something about as safe as C is currently - because CPUs are fundamentally unsafe and we need them to work somehow.

Nah. Most rust is safe rust. Even in the kernel, not much code actually interacts directly with raw hardware. The argument in favour of moving to rust isn't that it will remove 100% of memory safety bugs. Just that it'll hopefully remove most of them.

[UltraSane]

A million memory error bugs is used as a valid argument to stop using C and switch to rust where such bugs are impossible.