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 atmel_nand.

[1] 
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Tudor Ambarus <tudor.amba...@linaro.org>
Cc: Miquel Raynal <miquel.ray...@bootlin.com>
Cc: Richard Weinberger <rich...@nod.at>
Cc: Vignesh Raghavendra <vigne...@ti.com>
Cc: Nicolas Ferre <nicolas.fe...@microchip.com>
Cc: Alexandre Belloni <alexandre.bell...@bootlin.com>
Cc: Claudiu Beznea <claudiu.bez...@tuxon.dev>
Cc: linux-...@lists.infradead.org
Cc: linux-arm-ker...@lists.infradead.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/mtd/nand/raw/atmel/nand-controller.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c 
b/drivers/mtd/nand/raw/atmel/nand-controller.c
index 3f494f7c7ecb..4cb478bbee4a 100644
--- a/drivers/mtd/nand/raw/atmel/nand-controller.c
+++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
@@ -165,7 +165,7 @@ struct atmel_nand {
        struct atmel_pmecc_user *pmecc;
        struct gpio_desc *cdgpio;
        int numcs;
-       struct atmel_nand_cs cs[];
+       struct atmel_nand_cs cs[] __counted_by(numcs);
 };
 
 static inline struct atmel_nand *to_atmel_nand(struct nand_chip *chip)
-- 
2.34.1

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