Received-SPF: pass (google.com: domain of linux-kernel+bounces-78324-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <bc22e93196284ddece102929ae9f6636358e6716.camel@perches.com>
Subject: Re: [PATCH v2] checkpatch: add check for snprintf to scnprintf
From: Joe Perches <joe@perches.com>
To: Lee Jones <lee@kernel.org>
Cc: Justin Stitt <justinstitt@google.com>, Andy Whitcroft
 <apw@canonical.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>
Date: Fri, 23 Feb 2024 04:47:56 -0800
In-Reply-To: <20240223103845.GP10170@google.com>
References: <20240221-snprintf-checkpatch-v2-1-9baeb59dae30@google.com>
	 <bccc704fc78b362bbc57a79eb240219f5ec1548e.camel@perches.com>
	 <20240223103845.GP10170@google.com>
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: quoted-printable
User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) 
Precedence: bulk
MIME-Version: 1.0

On Fri, 2024-02-23 at 10:38 +0000, Lee Jones wrote:
> On Wed, 21 Feb 2024, Joe Perches wrote:
>=20
> > On Wed, 2024-02-21 at 22:11 +0000, Justin Stitt wrote:
> > > I am going to quote Lee Jones who has been doing some snprintf ->
> > > scnprintf refactorings:
> > >=20
> > > "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."
> > >=20
> > > To help prevent new instances of snprintf() from popping up, let's ad=
d a
> > > check to checkpatch.pl.
> > >=20
> > > Suggested-by: Finn Thain <fthain@linux-m68k.org>
> > > Signed-off-by: Justin Stitt <justinstitt@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].
> > >=20
> > > [1]: https://lore.kernel.org/all/0f9c95f9-2c14-eee6-7faf-635880edcea4=
@linux-m68k.org/
> >=20
> > > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> > []
> > > @@ -7012,6 +7012,12 @@ sub process {
> > >  			     "Prefer strscpy, strscpy_pad, or __nonstring over strncpy - =
see: https://github.com/KSPP/linux/issues/90\n" . $herecurr);
> > >  		}
> > > =20
> > > +# snprintf uses that should likely be {v}scnprintf
> > > +		if ($line =3D~ /\bsnprintf\s*\(\s*/) {
> > > +				WARN("SNPRINTF",
> > > +				     "Prefer scnprintf over snprintf\n" . $herecurr);
> >=20
> > There really should be some sort of reference link here
> > similar to the one above this.
> >=20
> > Also, I rather doubt _all_ of these should be changed just
> > for churn's sake.
>=20
> This is for new implementations only.
>=20
> Kees is planning on changing all of the current instances kernel-wide.

I saw that.  I also saw pushback.
Not just my own.

Creating a cocci script is easy.
Getting Linus and others to run it isn't.