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

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Date: Fri, 20 Oct 2023 10:40:12 -0700
From: Justin Stitt <justinstitt@...gle.com>
To: Christoph Hellwig <hch@....de>
Cc: Kees Cook <keescook@...omium.org>, 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 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.

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