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Banned C standard library functions in Git source code

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Re: Banned C standard library functions in Git source code

#31

Post by 1over137 »

kbumsik wrote: post #6
opticfluorine wrote: post #4

Earlier quoted context omitted.

Yes, and interestingly, because even when used correctly they "complicate audits". This is an interesting use of preprocessor macros, I'm strongly debating introducing something like this at work.

I'm not an expert in C, but then what's the issue with strncpy() or any "n" functions? It prevents overflow AFAIK. Also what is the alternative (memcpy?) and why?

strlcpy() is a nice alternative, it's from OpenBSD from 1996. Was later added to the other BSDs, Solaris and macOS. But, last I checked, Linux never added them. :(

https://www.sudo.ws/todd/papers/strlcpy.html

Re: Banned C standard library functions in Git source code

#35

Post by saagarjha »

alister wrote: post #26

I'm glad to see that setjmp() and longjmp() are still allowed. I'm just kidding by the way. For those C programmers who haven't encountered these before, it is a powerful way to do a "goto" in C. Powerful in the sense that you can jump anywhere, not limited to the same function. If it's used at all these days, it's used for exception handling. More info: https://en.wikipedia.org/wiki/Setjmp.h

I see zero use of those in the codebase, so perhaps they should be banned too. Or maybe they’re not on this list because nobody was using them already?

Re: Banned C standard library functions in Git source code

#36

Post by LukeShu »

saagarjha wrote: post #34

What does Git use instead for copying strings? snprintf? Edit: also interesting is a search for alloca: https://github.com/git/git/search?utf8=&q=alloca&type=

Git has an internal "strbuf" library https://github.com/git/git/blob/master/strbuf.h

Re: Banned C standard library functions in Git source code

#37

Post by asveikau »

noname120 wrote: post #21

Why is there no brief explanations in this code why each function is banned?

A C programmer reading this list knows exactly why they are there. It is not at all a controversial list.

Edit: I guess some down voter doesn't believe me but it continues to be true. They are all string functions. Most of them do not take an output buffer size, so a source string exceeding the destination buffer will overflow. Others, like strncpy, take an output buffer size but will not null terminate when exceeded, so the buffer size must be reduced by 1 by the caller and potentially manually terminates, which is too easy to not consider. But any C programmer with significant experience already knows these pitfalls. So it's not controversial.

Re: Banned C standard library functions in Git source code

#38

Post by zsrxx »

adamnemecek wrote: post #27
stiff wrote: post #11

Looks like Git has its own string type: https://github.com/git/git/blob/master/strbuf.h https://github.com/git/git/blob/master/strbuf.c See this for the story of why strncpy/strncat are insecure: https://en.wikipedia.org/wiki/C_string_handling#Replacements

Like essentially all C programs.

What's a good library for this kind of boilerplate? A lightweight one if possible, i.e. not fucking glib
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