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

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Message-ID: <202310201127.DA7EDAFE4D@keescook>
Date: Fri, 20 Oct 2023 11:30:49 -0700
From: Kees Cook <keescook@...omium.org>
To: Christoph Hellwig <hch@....de>
Cc: 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 10:40:12AM -0700, Justin Stitt wrote:
> On Thu, Oct 19, 2023 at 9:46 PM Christoph Hellwig <hch@....de> wrote:
> >
> > On Wed, Oct 18, 2023 at 11:01:54PM -0700, Kees Cook wrote:
> > > Almost all of the remaining strncpy() usage is just string to string
> > > copying, but the corner cases that are being spun out that aren't
> > > strscpy() or strscpy_pad() are covered by strtomem(), kmemdup_nul(),
> > > and memcpy(). Each of these are a clear improvement since they remove
> > > the ambiguity of the intended behavior. Using seq_buf ends up being way
> > > more overhead than is needed.
> >
> > I'm really not sure strscpy is much of an improvement.  In this particular
> > case in most other places we simply use a snprintf for nqns, which seems
> > useful here to if we don't want the full buf.
> >
> > But switching to a completely undocumented helper like strscpy seems not
> > useful at all.

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?

> 
> 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

-- 
Kees Cook