linux-hardening - Re: [PATCH][next] scsi: aacraid: Replace one-element array with flexible-array member

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Date:   Tue, 13 Apr 2021 07:04:11 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Kees Cook <keescook@...omium.org>
Cc:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Adaptec OEM Raid Solutions <aacraid@...rosemi.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] scsi: aacraid: Replace one-element array with
 flexible-array member

On Tue, 2021-04-13 at 00:45 -0500, Gustavo A. R. Silva wrote:
> Hi Martin,
> 
> On 4/12/21 23:52, Martin K. Petersen wrote:
> 
> > Silencing analyzer warnings shouldn't be done at the expense of
> > human
> > readers. If it is imperative to switch to flex_array_size() to
> > quiesce
> > checker warnings, please add a comment in the code explaining that
> > the
> > size evaluates to nseg_new-1 sge_ieee1212 structs.
> 
> Done:
> 	
> https://lore.kernel.org/lkml/20210413054032.GA276102@embeddedor/

I think the reason everyone gets confused is that they think the first
argument should do something.  If flex_array_size had been defined

#define flex_array_size(p, count)			\
	array_size(count,				\
		    sizeof(*(p)) + __must_be_array(p))

Then we could have used

flex_array_size(sge, nseg_new - 1)

or

flex_array_size(rio->sge, nseg_new - 1)

and everyone would have understood either expression.  This would also
have been useful, as the first example demonstrates, when we have a
pointer rather than a flexible member ... although that means the macro
likely needs a new name.

However, perhaps just do

array_size(nseg_new - 1, sizeof(*sge));

And lose the comment?

James