linux-kernel - Re: [PATCH v4 1/3] auxdisplay: Add 7-segment LED display driver

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Message-ID: <CAMuHMdXF+12PHa5A7WeyPMfvsGcJN13WaPuCbTmJU52Huq=osA@mail.gmail.com>
Date: Tue, 5 Mar 2024 09:23:07 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Chris Packham <chris.packham@...iedtelesis.co.nz>
Cc: andy@...nel.org, robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, 
	conor+dt@...nel.org, andrew@...n.ch, gregory.clement@...tlin.com, 
	sebastian.hesselbarth@...il.com, lee@...nel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-leds@...r.kernel.org
Subject: Re: [PATCH v4 1/3] auxdisplay: Add 7-segment LED display driver

Hi Chris,

On Tue, Mar 5, 2024 at 4:59 AM Chris Packham
<chris.packham@...iedtelesis.co.nz> wrote:
> Add a driver for a 7-segment LED display. At the moment only one
> character is supported but it should be possible to expand this to
> support more characters and/or 14-segment displays in the future.
>
> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>

Sorry, I spoke too soon...

> --- /dev/null
> +++ b/drivers/auxdisplay/seg-led-gpio.c

> +static void seg_led_update(struct work_struct *work)
> +{
> +       struct seg_led_priv *priv = container_of(work, struct seg_led_priv, work.work);
> +       struct linedisp *linedisp = &priv->linedisp;
> +       struct linedisp_map *map = linedisp->map;
> +       DECLARE_BITMAP(values, 8) = { 0 };
> +
> +       bitmap_set_value8(values, map_to_seg7(&map->map.seg7, linedisp->buf[0]), 0);
> +
> +       gpiod_set_array_value_cansleep(priv->segment_gpios->ndescs, priv->segment_gpios->desc,
> +                                      priv->segment_gpios->info, values);
> +}

> +static int seg_led_probe(struct platform_device *pdev)
> +{
> +       struct seg_led_priv *priv;
> +       struct device *dev = &pdev->dev;
> +
> +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
> +       if (!priv)
> +               return -ENOMEM;
> +
> +       platform_set_drvdata(pdev, priv);
> +
> +       priv->segment_gpios = devm_gpiod_get_array(dev, "segment", GPIOD_OUT_LOW);
> +       if (IS_ERR(priv->segment_gpios))
> +               return PTR_ERR(priv->segment_gpios);

This needs some validation of priv->segment_gpios->ndescs, else the
call to gpiod_set_array_value_cansleep() in seg_led_update() may
trigger an out-of-bounds access of the values bitmap.

> +
> +       return linedisp_register(&priv->linedisp, dev, 1, &seg_led_linedisp_ops);
> +}

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