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

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Date:   Tue, 25 Feb 2020 08:00:58 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Horia Geanta <horia.geanta@....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 2/25/20 07:44, Horia Geanta wrote:
> 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>
> 

Thank you, Horia.
--
Gustavo

> 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
>