As opposed to the false positives returned by comparing '*' to itself.
Why * specifically? Why not some random guid generated before committing, if it's so important to not let buggy software crash?
Why * specifically? Why not some random guid generated before committing, if it's so important to not let buggy software crash?
But buggy software might not crash; it might compare NULL == NULL and misbehave, instead.
So there's really no good option here, which is why C is a rancid choice of language for publicly-usable APIs. But we're stuck with it. So it goes.
But issues caused by folks forgetting to check errno, miscomparing NULL to NULL when calling multiple APIs, dereferencing external-API-returned NULL due to missed error checking, mishandling inherited errno after successful action, or--the most common--mishandling negative integer return sentinels meant to indicate errors? Those are incredibly common.
Standard C api calls return an integer, which is 0 on success or nonzero on error. Ignoring it is an intentional choice. `errno` is the hack that shouldn't really exist because it's trivially easy to forget to check that and also has issues with threading (patched by making it a thread local) and more recently, coroutines (which admit no general purpose patch because they're a userspace construct).
Another reason why this is terrible is that it's unclear what the returned pointer's lifetime is. Is it until the next call to crypt? If so, is it thread-local like errno? If it's passed on to the user, is it safe to call free() on it, or is there a crypt_free function that should be called instead?
But all of this, and I mean all of it pales in comparison to returning '*' on error.
100% agree. This is an egregious failure. But C's error-handling story would be bad even without this, and the badness of C's error handling is what motivated the (bad) decision to return *.
It'd be great if we wrote systems software in a language that supported advanced features like...
checks notes
...returning multiple values.
Hell, even in VBA you had to at least spend the keystrokes to type "on error resume next".
If the password field contains some string that is not a valid result of crypt(3), for instance ! or *, the user will not
be able to use a unix password to log in (but the user may log in the system by other means).So they made the (very bad, but motivated by C's broken design/conventions) decision to return a magic string instead.
0. There are tons of libc functions that return NULL on failure, it is conventional way in C to indicate failure.
1. There's no much to decide, just fail to login if crypt() fails with NULL.
2. errno is standard way in C to check error code of a failing function, but in case of login you hardly need this, just fail!
I totally agree that fixing this issue in musl was a pretty dubious solution. Don't fix what's not broken, fix broken application instead. Publish a CVE if you cannot fix it.
I looked through FreeBSD source code for how they use crypt(), it's checked for NULL everywhere!
UPD: Except libpam. :(
Dude, they documented their rationale. It was dumb and wrong but totally relatable. Irresponsible users were getting crashes, and I’m sorry to tell you that for a lot of library maintainers
> Returning NULL on error is actually an excellent choice because most programs will crash if they try to use it without checking.
…is not something they want to write in responses to bug reports, even though it is quite true. It’s human nature to want to prevent your stuff causing problems for others, even if the problems are fully their fault. Most people cannot and will not be Steve “so don’t hold it like that” Jobs, for fear that their decision will be just as short-sighted as his was.
In this case, that was obviously the dead wrong call. But I’ve been in that seat, and “closed: user error” for the 100th time feels bad to write. Add to that a touch of misplaced cleverness, and you get “hey…what if we just returned an impossible string instead of an error?”
Evil requires motive or malice, and I’m having trouble coming up with those in this case. These patches weren’t concealed or miscategorized a la xz, the behavior was discussed in the open. They were just, in hindsight, really poor decisions made for ordinary reasons. Hanlon’s Razor and all that.
That’s why I’ve been harping on C being trash for shared-code APIs in these comments: bad decisions are gonna happen, and irresponsible users are forever, so can we maybe use tools that require you to put on a seat belt (mandatory error handling) before starting the car?
Agreed, but I can’t think of any other widespread ABIs that are better. Rust’s is not stable both C++ and Rust have concepts that don’t map into other languages well, so using them wholesale is a no go. So it would probably need to be a subset of those. Honestly just tagged unions would probably be enough. Maybe the solution is to get native tagged unions into C…
There is the concept of "defense in depth": having each layer of code and configuration be sane and secure. Even if you program in Rust, you should be vigilant in that sense. This kind of code amounts to removing one or two layers.
That's the job of a OSS library author.
You can argue that C has broken design/conventions, but the musl decision was really really awkward.