std.file functions and embedded NUL characters [CWE-158]

[JacintoChamplin]

On Tuesday, 5 August 2025 at 03:28:26 UTC, Steven Schveighoffer 
wrote:
> On Tuesday, 5 August 2025 at 02:47:22 UTC, kdevel wrote:
>> On Sunday, 3 August 2025 at 21:01:05 UTC, Steven Schveighoffer 
>> wrote:
>>> [...]
>>> The issue is going to be fixed, not sure if you saw my issue 
>>> report. It's quite an easy fix actually.
>>
>> Thanks but sorry I could not yet take a look.
>
> TL;DR: We can fix `tempCString` since we are always copying the 
> whole thing. So the issue is moot at that point.
>
>>> But just so you know, C also allows passing in C strings with 
>>> embedded null characters:
>>>
>>> ```c
>>> #include <unistd.h>
>>>
>>> int main() {
>>>    rmdir("hello\0world");
>>>    return 0;
>>> }
>>> ```
>>
>> On the one hand there is no such thing as a C string with 
>> embedded `NUL` (because the `NUL` terminates the string).
>>
>> On the other hand the `rmdir` function takes `const char 
>> *pathname`. Your code contains an array argument 
>> (`"hello\0world"`). According to C's rules this array decays 
>> into a pointer *before* `rmdir` is invoked. Thus one can 
>> hardly say that a string with embedded `NUL` is passed to the 
>> function.
>
> C does not give me an error for this code. Regardless of what 
> it "technically" is doing, you have the same issue there -- C 
> does not warn you or error on this concern. So it is 
> identically vulnerable to your test case.
>
>>> And we do expose `core.stdc.posix.unistd`.
>>
>> Yes. But in the D-function in question is `std.file.rmdir`.
>
> C already needs to caution people not to call this function 
> with embedded null string array. D can also do the same thing. 
> My point is, I don't imagine we need to "fix" the unistd 
> binding.
>
> Again, who's responsible for verification is a tradeoff. In 
> this case, we have an obvious answer for std.file.rmdir, 
> because we can fix `tempCString`. But it also could be solved 
> by just identifying what happens if you pass in such a string, 
> and put the onus on the user to check.
>
> -Steve

Thanks for your reply. It solved my problem.
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