Re: [PATCH] USB: serial: garmin_gps: annotate struct garmin_packet with __counted_by

[Nathan Chancellor]

On Wed, Jun 19, 2024 at 11:40:57AM +0200, Javier Carrasco wrote:
> Use the __counted_by compiler attribute for the data[] flexible array member
> to improve the results of array bound sanitizers.
> 
> Signed-off-by: Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>
> ---
> The size is assigned before the first reference to the flexible array
> (see pkt_add()), which allows for a straightforward annotation without
> further modifications.

Agreed, this seems like a reasonable patch in and of itself that should
work:

Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>

It might also make sense to change the pkt allocation to use
struct_size() instead of open coding it?

diff --git a/drivers/usb/serial/garmin_gps.c b/drivers/usb/serial/garmin_gps.c
index 670e942fdaaa..04946c1cbf6f 100644
--- a/drivers/usb/serial/garmin_gps.c
+++ b/drivers/usb/serial/garmin_gps.c
@@ -267,8 +267,7 @@ static int pkt_add(struct garmin_data *garmin_data_p,
 
 	/* process only packets containing data ... */
 	if (data_length) {
-		pkt = kmalloc(sizeof(struct garmin_packet)+data_length,
-								GFP_ATOMIC);
+		pkt = kmalloc(struct_size(pkt, data, data_length), GFP_ATOMIC);
 		if (!pkt)
 			return 0;
 

> ---
>  drivers/usb/serial/garmin_gps.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/serial/garmin_gps.c b/drivers/usb/serial/garmin_gps.c
> index 670e942fdaaa..57df6ad183ff 100644
> --- a/drivers/usb/serial/garmin_gps.c
> +++ b/drivers/usb/serial/garmin_gps.c
> @@ -104,7 +104,7 @@ struct garmin_packet {
>  	int               seq;
>  	/* the real size of the data array, always > 0 */
>  	int               size;
> -	__u8              data[];
> +	__u8              data[] __counted_by(size);
>  };
>  
>  /* structure used to keep the current state of the driver */
> 
> ---
> base-commit: 0c52056d9f77508cb6d4d68d3fc91c6c08ec71af
> change-id: 20240619-garmin_gps_counted_by-376545960353
> 
> Best regards,
> -- 
> Javier Carrasco <javier.carrasco.cruz@xxxxxxxxx>
>