Received-SPF: pass (google.com: domain of linux-kernel+bounces-162969-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Date: Mon, 29 Apr 2024 12:49:48 -0700
From: Kees Cook <keescook@chromium.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, Lee Jones <lee@kernel.org>,
	linux-hardening@vger.kernel.org, Finn Thain <fthain@linux-m68k.org>
Subject: Re: [PATCH v6] checkpatch: add check for snprintf to scnprintf
Message-ID: <202404291249.078D924@keescook>
References: <20240429-snprintf-checkpatch-v6-1-354c62c88290@google.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240429-snprintf-checkpatch-v6-1-354c62c88290@google.com>

On Mon, Apr 29, 2024 at 06:39:28PM +0000, 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>

Thanks!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook