Probably >50% of exploits these days target use-after-frees, not buffer overflows. I don’t have hard data though.
As for null pointer problems, while they may result in CVEs, they’re a pretty minor security concern since they generally only result in denial of service.
Edit 2: Here's some data: In an analysis by Google, the "most frequently exploited" vulnerability types for zero-day exploitation were use-after-free, command injection, and XSS [3]. Since command injection and XSS are not memory-unsafety vulnerabilities, that implies that use-after-frees are significantly more frequently exploited than other types of memory unsafety.
Edit: Zig previously had a GeneralPurposeAllocator that prevented use-after-frees of heap allocations by never reusing addresses. But apparently, four months ago [1], GeneralPurposeAllocator was renamed to DebugAllocator and a comment was added saying that the safety features "require the allocator to be quite slow and wasteful". No explicit reasoning was given for this change, but it seems to me like a concession that applications need high performance generally shouldn't be using this type of allocator. In addition, it appears that use-after-free is not caught for stack allocations [2], or allocations from some other types of allocators.
Note that almost the entire purpose of Rust's borrow checker is to prevent use-after-free. And the rest of its purpose is to prevent other issues that Zig also doesn't protect against: tagged-union type confusion and data races.
yeah I don't think the GPA is really a great strategy for detecting UAF, but it was a good try. It basically creates a new virtual page for each allocation, so the kernel gets involved and ?I think? there is more indirection for any given pointer access. So you can imagine why it wasn't great.
Anyways, I am optimistic that UAF can be prevented by static analysis:
Note since this sort of technique interfaces with the compiler, unless the dependency is in a .so file, it will detect UAF in dependencies too, whether or not the dependency chooses to run the static analysis as part of their software quality control.
Fair enough. In some sense you’re writing your own borrow checker. But (you may know this already) be warned: this has been tried many times for C++, with different levels of annotation burden imposed on programmers.
On one side are the many C++ “static analyzers” like Coverity or clang-analyzer, which work with unannotated C++ code. On the other side is the “Safe C++” proposal (safecpp.org), which is supposed to achieve full safety, but at the cost of basically transplanting Rust’s type system into C++, requiring all functions to have lifetime annotations and disallow mutable aliasing, and replacing the entire standard library with a new one that follows those rules. Between those two extremes there have been tools like the C++ Core Guidelines Checker and Clang’s lifetimebound attribute, which require some level of annotations, and in turn provide some level of checking.
So far, none of these have been particularly successful in preventing memory safety vulnerabilities. Static analyzers are widely used in industry but only find a fraction of bugs. Safe C++ will probably be too unpopular to make it into the spec. The intermediate solutions have some fundamental issues (see [1], though it’s written by the author of Safe C++ and may be biased), and in practice haven’t really taken off.
But I admit that only the “static analyzer” side of the solution space has been extensively explored. The other projects are just experiments whose lack of adoption may be due to inertia as much as inherent lack of merit.
And Zig may be different… I’m not a Zig programmer, but I have the impression that compared to C++ it encourages fewer allocations and smaller codebases, both of which may make lifetime analysis more tractable. It’s also a much younger language whose audience is necessarily much more open to change.
So we’ll see. Good luck - I’d sure like to see more low-level languages offering memory safety.
One of the key things in Sean's "Safe C++" is that, like Rust, it actually technically works. If we write software in the safe C++ dialect we get safe programs just as if we write ordinary safe (rather than ever invoking "unsafe") Rust we get safe programs. WG21 didn't take Safe C++ and it will most likely now be a minor footnote in history, but it did really work.
"I think this could be possible" isn't an enabling technology. If you write hard SF it's maybe useful to distinguish things which could happen from those which can't, but for practical purposes it only matters if you actually did it. Sean's proposed "Safe C++" did it, Zig, today, did not.
There are other obstacles - like adoption, as we saw for "Safe C++" - but they're predicated on having the technology at all, you cannot adopt technologies which don't exist, that's just make believe. Which I think is already the path WG21 has set out on.
> Safe C++ will probably be too unpopular to make it into the spec.
Not just that, but the committee accepted a paper that basically says it's design is against C++'s design principles, so it's effectively dead forever.
Here's somebody who was in the room explaining how this was agreed as standing policy for the C++ programming language.
"It was literally the last paper. Seen at the last hour. Of a really long week. Most everyone was elsewhere in other working group meetings assuming no meaningful work was going to happen."
Thanks! I think this could be implemented as a (3rd party?) compiler backend.
And yeah, if it gets done quickly enough (before 1.0?) it could get enough momentum that it gets accepted as "considered to be best practice".
Honestly, though, I think the big hurdle for C/C++ static analysis is that lots of dependencies get shipped around as .so's and once that happens it's sort of a black hole unless 1) the dependency's provider agrees to run the analysis or 2) you can easily shim to annotate what's going on in the library's headers. 2) is a pain in the ass, and begging for 1) can piss off the dependency's owner.
As for null pointer problems, while they may result in CVEs, they’re a pretty minor security concern since they generally only result in denial of service.
Edit 2: Here's some data: In an analysis by Google, the "most frequently exploited" vulnerability types for zero-day exploitation were use-after-free, command injection, and XSS [3]. Since command injection and XSS are not memory-unsafety vulnerabilities, that implies that use-after-frees are significantly more frequently exploited than other types of memory unsafety.
Edit: Zig previously had a GeneralPurposeAllocator that prevented use-after-frees of heap allocations by never reusing addresses. But apparently, four months ago [1], GeneralPurposeAllocator was renamed to DebugAllocator and a comment was added saying that the safety features "require the allocator to be quite slow and wasteful". No explicit reasoning was given for this change, but it seems to me like a concession that applications need high performance generally shouldn't be using this type of allocator. In addition, it appears that use-after-free is not caught for stack allocations [2], or allocations from some other types of allocators.
Note that almost the entire purpose of Rust's borrow checker is to prevent use-after-free. And the rest of its purpose is to prevent other issues that Zig also doesn't protect against: tagged-union type confusion and data races.
[1] https://github.com/ziglang/zig/commit/cd99ab32294a3c22f09615...
[2] https://github.com/ziglang/zig/issues/3180.
[3] https://cloud.google.com/blog/topics/threat-intelligence/202...