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@sang-engineering.com>
Cc: Peter Rosin <peda@axentia.se>
Cc: linux-i2c@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 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);
-- 
2.34.1

On Fri, Sep 22, 2023 at 10:49:59AM -0700, 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@sang-engineering.com>
> Cc: Peter Rosin <peda@axentia.se>
> Cc: linux-i2c@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Fixed a blank line and applied to for-next, thanks!

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@sang-engineering.com>
> Cc: Peter Rosin <peda@axentia.se>
> Cc: linux-i2c@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.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);