linux-kernel - Re: [PATCH] dmaengine: usb-dmac: Avoid format-overflow warning

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Date: Thu, 11 Jan 2024 11:41:54 +0000
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Vinod Koul <vkoul@...nel.org>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, 
	Tudor Ambarus <tudor.ambarus@...aro.org>, Kees Cook <keescook@...omium.org>, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org, 
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
Subject: Re: [PATCH] dmaengine: usb-dmac: Avoid format-overflow warning

Hi Geert,

Thank you for the review.

On Thu, Jan 11, 2024 at 9:05 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Prabhakar,
>
> On Wed, Jan 10, 2024 at 11:23 PM Prabhakar <prabhakar.csengg@...il.com> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...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=]
> >   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@...renesas.com>
>
> Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.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 *pdev)
> >         const enum dma_slave_buswidth widths = 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.
>
Agreed. So shall I drop Kees suggestion and leave the patch as is?

Cheers,
Prabhakar