linux-kernel - Re: [PATCH] crypto: Replace zero-length array with flexible-array member

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Message-ID: <VI1PR0402MB3485175AB5B3092409DC26AA98ED0@VI1PR0402MB3485.eurprd04.prod.outlook.com>
Date:   Tue, 25 Feb 2020 13:44:53 +0000
From:   Horia Geanta <horia.geanta@....com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Aymen Sghaier <aymen.sghaier@....com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Atul Gupta <atul.gupta@...lsio.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Breno Leitão <leitao@...ian.org>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Paulo Flabiano Smorigo <pfsmorigo@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
CC:     "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH] crypto: Replace zero-length array with flexible-array
 member

On 2/24/2020 6:18 PM, 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
> inadvertently introduced[3] to the codebase from now on.
> 
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
> 
> "Flexible array members have incomplete type, and so the sizeof operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
> 
> 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@...eddedor.com>
Reviewed-by: Horia Geantă <horia.geanta@....com>

for caam driver:

>  drivers/crypto/caam/caamalg.c              | 2 +-
>  drivers/crypto/caam/caamalg_qi.c           | 4 ++--
>  drivers/crypto/caam/caamalg_qi2.h          | 6 +++---
>  drivers/crypto/caam/caamhash.c             | 2 +-

Thanks,
Horia