linux-kernel - Re: [PATCH] USB: serial: ti_usb_3410_5052: Replace zero-length array with flexible-array member

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Message-ID: <20200212075929.GE4150@localhost>
Date:   Wed, 12 Feb 2020 08:59:29 +0100
From:   Johan Hovold <johan@...nel.org>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc:     Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: serial: ti_usb_3410_5052: Replace zero-length array
 with flexible-array member

On Tue, Feb 11, 2020 at 05:24:20PM -0600, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array member[1][2],
> introduced in C99:
> 
> struct foo {
>         int stuff;
>         struct boo array[];
> };
> 
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertenly introduced[3] to the codebase from now on.
> 
> This issue was found with the help of Coccinelle.

Same here, the scripts may need to be updated as you missed a couple of
instances:

	$ git grep '\[0\];' drivers/usb/serial
	...
	drivers/usb/serial/io_usbvend.h:        __u8    Data[0];                // Data starts here
	drivers/usb/serial/io_usbvend.h:        __u8    Data[0];                // Download starts here
	...

Could you replace these as well so that is done in one patch per
subsystem?

> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/usb/serial/ti_usb_3410_5052.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/usb/serial/ti_usb_3410_5052.c b/drivers/usb/serial/ti_usb_3410_5052.c
> index dd0ad67aa71e..db3ab25d9228 100644
> --- a/drivers/usb/serial/ti_usb_3410_5052.c
> +++ b/drivers/usb/serial/ti_usb_3410_5052.c
> @@ -219,7 +219,7 @@ struct ti_write_data_bytes {
>  	u8	bDataCounter;
>  	__be16	wBaseAddrHi;
>  	__be16	wBaseAddrLo;
> -	u8	bData[0];
> +	u8	bData[];
>  } __packed;
>  
>  struct ti_read_data_request {
> @@ -234,7 +234,7 @@ struct ti_read_data_bytes {
>  	__u8	bCmdCode;
>  	__u8	bModuleId;
>  	__u8	bErrorCode;
> -	__u8	bData[0];
> +	__u8	bData[];
>  } __packed;
>  
>  /* Interrupt struct */

Thanks,
Johan