linux-kernel - Re: [PATCH] staging: wlan-ng: Use flexible-array for one / zero-length arrays

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Message-ID: <Y1vaR0olLH9+bJbk@kadam>
Date:   Fri, 28 Oct 2022 16:33:59 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Deepak R Varma <drv@...lo.com>
Cc:     outreachy@...ts.linux.dev,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: wlan-ng: Use flexible-array for one /
 zero-length arrays

On Fri, Oct 28, 2022 at 06:08:13PM +0530, Deepak R Varma wrote:
> Flexible-array member should be used instead of one or zero member to
> meet the need for having a dynamically sized trailing elements in a
> structure. Refer to links [1] and [2] for detailed guidance on this
> suggestion.
> 
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays
> 
> Issue identified using coccicheck.
> 
> Signed-off-by: Deepak R Varma <drv@...lo.com>
> ---
>  drivers/staging/wlan-ng/p80211mgmt.h  | 8 ++++----
>  drivers/staging/wlan-ng/p80211types.h | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/staging/wlan-ng/p80211mgmt.h b/drivers/staging/wlan-ng/p80211mgmt.h
> index 1ef30d3f3159..d6fe52de2c8f 100644
> --- a/drivers/staging/wlan-ng/p80211mgmt.h
> +++ b/drivers/staging/wlan-ng/p80211mgmt.h
> @@ -229,14 +229,14 @@ struct wlan_ie {
>  struct wlan_ie_ssid {
>  	u8 eid;
>  	u8 len;
> -	u8 ssid[1];		/* may be zero, ptrs may overlap */
> +	u8 ssid[];		/* may be zero, ptrs may overlap */

How have you ensured that changing this from a 1 byte array to a zero
byte array does not break anything?  It's not uncommon for a people
to do math like "size - 1 + length".  The "- 1" would be to take the
1 element into consideration.

I was trying to read through this code to check your work, but then
you sent a second patch which also does not explain how you are auditing
your changes.  Can you go a bit slower?

regards,
dan carpenter