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 hpets.

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

Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/char/hpet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
index 3b2159416e62..807c389510de 100644
--- a/drivers/char/hpet.c
+++ b/drivers/char/hpet.c
@@ -92,7 +92,7 @@ struct hpets {
 	unsigned long hp_delta;
 	unsigned int hp_ntimer;
 	unsigned int hp_which;
-	struct hpet_dev hp_dev[];
+	struct hpet_dev hp_dev[] __counted_by(hp_ntimer);
 };
 
 static struct hpets *hpets;
-- 
2.34.1

On 9/22/23 11:53, 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 hpets.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Clemens Ladisch <clemens@ladisch.de>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Kees Cook <keescook@chromium.org>

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

Thanks
-- 
Gustavo

> ---
>   drivers/char/hpet.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
> index 3b2159416e62..807c389510de 100644
> --- a/drivers/char/hpet.c
> +++ b/drivers/char/hpet.c
> @@ -92,7 +92,7 @@ struct hpets {
>   	unsigned long hp_delta;
>   	unsigned int hp_ntimer;
>   	unsigned int hp_which;
> -	struct hpet_dev hp_dev[];
> +	struct hpet_dev hp_dev[] __counted_by(hp_ntimer);
>   };
>   
>   static struct hpets *hpets;