Bugs Rust won't catch

I just want to mention that I disagree with the section titled "Rule: Resolve Paths Before Comparing Them". Generally, it is better to make calls to fstat and compare the st_dev and st_ino. However, that was mentioned in the article. A side effect that seems less often considered is the performance impact. Here is an example in practice:

  $ mkdir -p $(yes a/ | head -n $((32 * 1024)) | tr -d '\n')
  $ while cd $(yes a/ | head -n 1024 | tr -d '\n'); do :; done 2>/dev/null
  $ echo a > file
  $ time cp file copy

  real 0m0.010s
  user 0m0.002s
  sys 0m0.003s
  $ time uu_cp file copy

  real 0m12.857s
  user 0m0.064s
  sys 0m12.702s

Also, the larger point still stands, but the article says "The Rust rewrite has shipped zero of these [memory saftey bugs], over a comparable window of activity." However, this is not true [2]. :)

[1] https://www.gnu.org/prep/standards/standards.html#Semantics [2] https://github.com/advisories/GHSA-w9vv-q986-vj7x

They knew how to write Rust, but clearly weren't sufficiently experienced with Unix APIs, semantics, and pitfalls. Most of those mistakes are exceedingly amateur from the perspective of long-time GNU coreutils (or BSD or Solaris base) developers, issues that were identified and largely hashed out decades ago, notwithstanding the continued long tail of fixes--mostly just a trickle these days--to the old codebases.

> The trap is that get_user_by_name ends up loading shared libraries from the new root filesystem to resolve the username. An attacker who can plant a file in the chroot gets to run code as uid 0.

To me such a get_user_by_name function is like a booby trap, an accident that is waiting to happen. You need to have user data, you have this get_user_by_name function, and then it goes and starts loading shared libraries. This smells like mixing of concerns to me. I'd say, either split getting the user data and loading any shared libraries in two separate functions, or somehow make it clear in the function name what it is doing.

The code gets silently encumbered with those lessons, and unless they are documented, there's a lot of hidden work that needs to be done before you actually reach parity.

TFA is a good list of this exact sort of thing.

Before you call people amateur for it, also consider it's one of the most softwarey things about writing software. It was bound to happen unless coreutils had really good technical docs and included tests for these cases that they ignored.

It's actually even worse than that somewhat, because the attacker with write access to a parent directory can mess with hard links as well... sure, it only messes with the regular files themselves but there is basically no mitigations. See e.g. [0] and other posts on the site.

[0] https://michael.orlitzky.com/articles/posix_hardlink_heartac...

...

[List of bugs a diligent person would be mindful of, unix expert or not]

---

Only conclusion I can make is, unfortunately, the people writing these tools are not good software developers.

For comparison, I'm neither a unix neckbeard not a rust expert, but I'm using rust to write a music player using LLMs and the amount of tokens I've sunk into watching for DoS panics or dropped errors is pretty substantial. Why? Because I don't want my music player to suck! Simple as that.

Pretty shocking to see the lack of basic thought going into writing what is meant to be critical infrastructure. Wow, honestly pathetic. Sorry to be so negative and for this word choice, but I am shocked and disappointed. The title of this article should be "Rust can't stop you from not giving a fuck" or "rust can't stop you from being careless."

That's kind of horrifying. Is there a reliable list somewhere of all the functions that do that? Is that list considered stable?

Rust won't catch it, but now the agents will.

Edit: https://gist.github.com/fschutt/cc585703d52a9e1da8a06f9ef93c... for anyone who needs copying this

Granted, the uutils authors are well experienced in Rust, but it is not enough for a large-scale rewrite like this and you can't assume that it's "secure" because of memory safety.

In this case, this post tells us that Unix itself has thousands of gotchas and re-implementing the coreutils in Rust is not a silver bullet and even the bugs Unix (and even the POSIX standard) has are part of the specification, and can be later to be revealed as vulnerabilities in reality.

I hate to armchair general, but I clicked on this article expecting subtle race conditions or tricky ambiguous corners of the POSIX standard, and instead found that it seems to be amateur hour in uutils.

I'd be interested in a comparison with the amount of bugs and CVE's in GNU coreutils at the start of its lifetime, and compare it with this rewrite. Same with the number of memory bugs that are impossible in (safe) Rust.

Don't just downvote me, tell me how I'm wrong.