linux-hardening - Re: the nul-terminated string helper desk chair rearrangement

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Date: Thu, 26 Oct 2023 12:01:48 +0200
From: Christoph Hellwig <hch@....de>
To: Kees Cook <keescook@...omium.org>
Cc: Christoph Hellwig <hch@....de>, Justin Stitt <justinstitt@...gle.com>,
	Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>, linux-nvme@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
	ksummit@...ts.linux.dev
Subject: Re: the nul-terminated string helper desk chair rearrangement

On Fri, Oct 20, 2023 at 11:30:49AM -0700, Kees Cook wrote:
> I'm curious where you looked and didn't find documentation -- perhaps
> there is an improvement to be made to aim one to where the existing
> documentation lives?

My order was the following:

 - look for kernel doc on the main function implementation in
   lib/string.c (as found by a grep for an EXPORT_SYMBOL for it)
 - after not finding it there, but seeing that it has an ifdef for
   an arch override, which turns out to be unused
 - then I grepped the Documentation/ directory for it, and while
   there are quite a few matches for strscpy, they are largely
   in examples, with the only text referring to strscpy being
   Documentation/process/deprecated.rst that tells you to use it
   instead of strcpy, but not how it actually works
 - after that I realized that some people put the kerneldoc on
   the declaration, so I looked at that in string.h, but couldn't
   find it.

> > There's some docs at [1]. Perhaps there could be more?
> > 
> > [1]: https://elixir.bootlin.com/linux/v6.6-rc6/source/include/linux/fortify-string.h#L292
> 
> Right, And it's even valid kern-doc, which gets rendered in the kernel
> API docs, along with all the other string functions:
> https://docs.kernel.org/core-api/kernel-api.html#c.strscpy

Well, I never use the generated kerneldoc because it's much harder than
just grepping the tree, but indeed it exists even if it's hidden in
the most obsfucated way.  But at least I know now!