Received-SPF: pass (google.com: domain of linux-kernel+bounces-23289-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Precedence: bulk
MIME-Version: 1.0
References: <20240110222210.193479-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
In-Reply-To: <20240110222210.193479-1-prabhakar.mahadev-lad.rj@bp.renesas.com>
From: Geert Uytterhoeven <geert@linux-m68k.org>
Date: Thu, 11 Jan 2024 10:05:00 +0100
Message-ID: <CAMuHMdXSLBARbtc91F=cWqTdL+UcT4wJbr0_m5+iz_6BXA4Acw@mail.gmail.com>
Subject: Re: [PATCH] dmaengine: usb-dmac: Avoid format-overflow warning
To: Prabhakar <prabhakar.csengg@gmail.com>
Cc: Vinod Koul <vkoul@kernel.org>, =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= <u.kleine-koenig@pengutronix.de>, 
	Tudor Ambarus <tudor.ambarus@linaro.org>, Kees Cook <keescook@chromium.org>, 
	dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-renesas-soc@vger.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable

Hi Prabhakar,

On Wed, Jan 10, 2024 at 11:23=E2=80=AFPM Prabhakar <prabhakar.csengg@gmail.=
com> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
>
> gcc points out that the fix-byte buffer might be too small:
> drivers/dma/sh/usb-dmac.c: In function 'usb_dmac_probe':
> drivers/dma/sh/usb-dmac.c:720:34: warning: '%u' directive writing between=
 1 and 10 bytes into a region of size 3 [-Wformat-overflow=3D]
>   720 |         sprintf(pdev_irqname, "ch%u", index);
>       |                                  ^~
> In function 'usb_dmac_chan_probe',
>     inlined from 'usb_dmac_probe' at drivers/dma/sh/usb-dmac.c:814:9:
> drivers/dma/sh/usb-dmac.c:720:31: note: directive argument in the range [=
0, 4294967294]
>   720 |         sprintf(pdev_irqname, "ch%u", index);
>       |                               ^~~~~~
> drivers/dma/sh/usb-dmac.c:720:9: note: 'sprintf' output between 4 and 13 =
bytes into a destination of size 5
>   720 |         sprintf(pdev_irqname, "ch%u", index);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Maximum number of channels for USB-DMAC as per the driver is 1-99 so use
> u8 instead of unsigned int/int for DMAC channel indexing and make the
> pdev_irqname string long enough to avoid the warning.
>
> While at it use scnprintf() instead of sprintf() to make the code more
> robust.
>
> Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

One nit below.

> --- a/drivers/dma/sh/usb-dmac.c
> +++ b/drivers/dma/sh/usb-dmac.c

> @@ -768,8 +768,8 @@ static int usb_dmac_probe(struct platform_device *pde=
v)
>         const enum dma_slave_buswidth widths =3D USB_DMAC_SLAVE_BUSWIDTH;
>         struct dma_device *engine;
>         struct usb_dmac *dmac;
> -       unsigned int i;
>         int ret;
> +       u8 i;

Personally, I'm not much a fan of making loop counters smaller than
(unsigned) int.  If you do go this way, there are more loops over all
channels still using int.

Gr{oetje,eeting}s,

                        Geert

--=20
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k=
org

In personal conversations with technical people, I call myself a hacker. Bu=
t
when I'm talking to journalists I just say "programmer" or something like t=
hat.
                                -- Linus Torvalds