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

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Date: Thu, 11 Jan 2024 10:00:53 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Prabhakar <prabhakar.csengg@...il.com>
Cc: Vinod Koul <vkoul@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Biju Das <biju.das.jz@...renesas.com>, 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: sh: rz-dmac: Avoid format-overflow warning

Hi Prabhakar,

On Wed, Jan 10, 2024 at 11:27 PM Prabhakar <prabhakar.csengg@...il.com> wrote:
> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
>
> The max channel count for RZ DMAC is 16, hence use u8 instead of unsigned
> int and make the pdev_irqname string long enough to avoid the warning.

Note that the danger lies into someone changing
RZ_DMAC_MAX_CHANNELS later...

> This fixes the below issue:
> drivers/dma/sh/rz-dmac.c: In function ‘rz_dmac_probe’:
> drivers/dma/sh/rz-dmac.c:770:34: warning: ‘%u’ directive writing between 1 and 10 bytes into a region of size 3 [-Wformat-overflow=]
>   770 |         sprintf(pdev_irqname, "ch%u", index);
>       |                                  ^~
> In function ‘rz_dmac_chan_probe’,
>     inlined from ‘rz_dmac_probe’ at drivers/dma/sh/rz-dmac.c:910:9:
> drivers/dma/sh/rz-dmac.c:770:31: note: directive argument in the range [0, 4294967294]
>   770 |         sprintf(pdev_irqname, "ch%u", index);
>       |                               ^~~~~~
> drivers/dma/sh/rz-dmac.c:770:9: note: ‘sprintf’ output between 4 and 13 bytes into a destination of size 5
>   770 |         sprintf(pdev_irqname, "ch%u", index);
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> 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>

Some nits below...

> --- a/drivers/dma/sh/rz-dmac.c
> +++ b/drivers/dma/sh/rz-dmac.c
> @@ -845,9 +845,9 @@ static int rz_dmac_probe(struct platform_device *pdev)
>         struct dma_device *engine;
>         struct rz_dmac *dmac;
>         int channel_num;
> -       unsigned int i;
>         int ret;
>         int irq;
> +       u8 i;

Personally, I'm not much a fan of making loop counters smaller than
(unsigned) int.  If you do go this way, you should change channel_num
to u8, too, just like i in rz_dmac_remove().

>
>         dmac = devm_kzalloc(&pdev->dev, sizeof(*dmac), GFP_KERNEL);
>         if (!dmac)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds