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

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Date: Fri, 20 Oct 2023 06:46:45 +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 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.