[PATCH] i2c: mux: demux-pinctrl: Annotate struct i2c_demux_pinctrl_priv with __counted_by

[Kees Cook <keescook@chromium.org>]

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