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Date: Thu, 11 Apr 2024 07:57:49 +0100
From: Lee Jones <lee@kernel.org>
To: Justin Stitt <justinstitt@google.com>
Cc: Andy Whitcroft <apw@canonical.com>, Joe Perches <joe@perches.com>,
	Dwaipayan Ray <dwaipayanray1@gmail.com>,
	Lukas Bulwahn <lukas.bulwahn@gmail.com>,
	linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
	Kees Cook <keescook@chromium.org>,
	Finn Thain <fthain@linux-m68k.org>
Subject: Re: [PATCH v4] checkpatch: add check for snprintf to scnprintf
Message-ID: <20240411065749.GC6194@google.com>
References: <20240408-snprintf-checkpatch-v4-1-8697c96ac94b@google.com>
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In-Reply-To: <20240408-snprintf-checkpatch-v4-1-8697c96ac94b@google.com>

On Mon, 08 Apr 2024, Justin Stitt wrote:

> I am going to quote Lee Jones who has been doing some snprintf ->
> scnprintf refactorings:
> 
> "There is a general misunderstanding amongst engineers that
> {v}snprintf() returns the length of the data *actually* encoded into the
> destination array.  However, as per the C99 standard {v}snprintf()
> really returns the length of the data that *would have been* written if
> there were enough space for it.  This misunderstanding has led to
> buffer-overruns in the past.  It's generally considered safer to use the
> {v}scnprintf() variants in their place (or even sprintf() in simple
> cases).  So let's do that."
> 
> To help prevent new instances of snprintf() from popping up, let's add a
> check to checkpatch.pl.
> 
> Suggested-by: Finn Thain <fthain@linux-m68k.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Changes in v4:
> - also check for vsnprintf variant (thanks Bill)
> - Link to v3: https://lore.kernel.org/r/20240315-snprintf-checkpatch-v3-1-a451e7664306@google.com
> 
> Changes in v3:
> - fix indentation
> - add reference link (https://github.com/KSPP/linux/issues/105) (thanks Joe)
> - Link to v2: https://lore.kernel.org/r/20240221-snprintf-checkpatch-v2-1-9baeb59dae30@google.com
> 
> Changes in v2:
> - Had a vim moment and deleted a character before sending the patch.
> - Replaced the character :)
> - Link to v1: https://lore.kernel.org/r/20240221-snprintf-checkpatch-v1-1-3ac5025b5961@google.com
> ---
> From a discussion here [1].
> 
> [1]: https://lore.kernel.org/all/0f9c95f9-2c14-eee6-7faf-635880edcea4@linux-m68k.org/
> ---
>  scripts/checkpatch.pl | 6 ++++++
>  1 file changed, 6 insertions(+)

Reviewed-by: Lee Jones <lee@kernel.org>

-- 
Lee Jones [李琼斯]