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

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

[Gustavo A. R. Silva]

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.

[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@embeddedor.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 */
-- 
2.25.0

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

[Johan Hovold]

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@embeddedor.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

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

[Gustavo A. R. Silva]

On 2/12/20 01:59, Johan Hovold wrote:
> 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?
> 

Sure thing. I'll do that.

Thanks for the feedback.
--
Gustavo