Re: [PATCH] usb: gadget: f_midi: Annotate struct f_midi with __counted_by

[Gustavo A. R. Silva]

On 9/15/23 13:59, 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 f_midi.
> 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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: John Keeping <john@xxxxxxxxxxxxx>
> Cc: Peter Chen <peter.chen@xxxxxxx>
> Cc: Hulk Robot <hulkci@xxxxxxxxxx>
> Cc: Allen Pais <allen.lkml@xxxxxxxxx>
> Cc: Will McVicker <willmcvicker@xxxxxxxxxx>
> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
> Cc: Zhang Qilong <zhangqilong3@xxxxxxxxxx>
> Cc: linux-usb@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

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

Thanks
--
Gustavo

> ---
>   drivers/usb/gadget/function/f_midi.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
> index 2d02f25f9597..033e347554db 100644
> --- a/drivers/usb/gadget/function/f_midi.c
> +++ b/drivers/usb/gadget/function/f_midi.c
> @@ -99,7 +99,7 @@ struct f_midi {
>   	unsigned int in_last_port;
>   	unsigned char free_ref;
>   
> -	struct gmidi_in_port	in_ports_array[/* in_ports */];
> +	struct gmidi_in_port	in_ports_array[] __counted_by(in_ports);
>   };
>   
>   static inline struct f_midi *func_to_midi(struct usb_function *f)
> @@ -1349,6 +1349,7 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>   		status = -ENOMEM;
>   		goto setup_fail;
>   	}
> +	midi->in_ports = opts->in_ports;
>   
>   	for (i = 0; i < opts->in_ports; i++)
>   		midi->in_ports_array[i].cable = i;
> @@ -1359,7 +1360,6 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>   		status = -ENOMEM;
>   		goto midi_free;
>   	}
> -	midi->in_ports = opts->in_ports;
>   	midi->out_ports = opts->out_ports;
>   	midi->index = opts->index;
>   	midi->buflen = opts->buflen;