linux-hardening - Re: [PATCH] i2c: mux: demux-pinctrl: Annotate struct i2c_demux_pinctrl_priv with __counted

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Date: Sat, 23 Sep 2023 10:26:43 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
 Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Peter Rosin <peda@...ntia.se>, linux-i2c@...r.kernel.org,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] i2c: mux: demux-pinctrl: Annotate struct
 i2c_demux_pinctrl_priv with __counted_by



On 9/22/23 11:49, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct i2c_demux_pinctrl_priv.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>
> Cc: Peter Rosin <peda@...ntia.se>
> Cc: linux-i2c@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
-- 
Gustavo

> ---
>   drivers/i2c/muxes/i2c-demux-pinctrl.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/muxes/i2c-demux-pinctrl.c b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> index a3a122fae71e..5e15d8777229 100644
> --- a/drivers/i2c/muxes/i2c-demux-pinctrl.c
> +++ b/drivers/i2c/muxes/i2c-demux-pinctrl.c
> @@ -32,7 +32,7 @@ struct i2c_demux_pinctrl_priv {
>   	const char *bus_name;
>   	struct i2c_adapter cur_adap;
>   	struct i2c_algorithm algo;
> -	struct i2c_demux_pinctrl_chan chan[];
> +	struct i2c_demux_pinctrl_chan chan[] __counted_by(num_chan);
>   };
>   
>   static int i2c_demux_master_xfer(struct i2c_adapter *adap, struct i2c_msg msgs[], int num)
> @@ -226,6 +226,8 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
>   	if (!priv || !props)
>   		return -ENOMEM;
>   
> +	priv->num_chan = num_chan;
> +
>   	err = of_property_read_string(np, "i2c-bus-name", &priv->bus_name);
>   	if (err)
>   		return err;
> @@ -248,8 +250,6 @@ static int i2c_demux_pinctrl_probe(struct platform_device *pdev)
>   		of_changeset_init(&priv->chan[i].chgset);
>   		of_changeset_update_property(&priv->chan[i].chgset, adap_np, &props[i]);
>   	}
> -
> -	priv->num_chan = num_chan;
>   	priv->dev = &pdev->dev;
>   
>   	platform_set_drvdata(pdev, priv);