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

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Date:   Fri, 28 Oct 2022 19:11:00 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Dan Carpenter <dan.carpenter@...cle.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 04:33:59PM +0300, Dan Carpenter wrote:
> 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.

Hi Dan,
I did a code review to understand how this structure member is used and did not
find any computations you mentioned. I would certainly like to receive your feedback
as well.

>
> 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?

My apologies for rushing patches in. I will hold on for feedback on these
patches before turning in any new patch involving similar change. I hope it is
okay to send a different type of patch though. Please correct if I am wrong.

Thank you for looking into the patches. Appreciate your time and feedback.

./drv


>
> regards,
> dan carpenter
>