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

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Message-ID: <75ab6118-6ddd-5ef6-0a12-1d2fd0253f68@linux.intel.com>
Date:   Thu, 17 Feb 2022 10:57:10 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Stephen Kitt <steve@....org>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Daniel Baluta <daniel.baluta@....com>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        sound-open-firmware@...a-project.org,
        linux-hardening@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] ASoC: SOF: Replace zero-length array with flexible-array
 member



On 2/17/22 10:44, Gustavo A. R. Silva wrote:
> On Thu, Feb 17, 2022 at 02:27:55PM +0100, Stephen Kitt wrote:
>> There is a regular need in the kernel to provide a way to declare having
>> a dynamically sized set of trailing elements in a structure. Kernel code
>> should always use "flexible array members"[1] for these cases. The older
>> style of one-element or zero-length arrays should no longer be used[2].
>>
>> This helps with the ongoing efforts to globally enable -Warray-bounds
>> and get us closer to being able to tighten the FORTIFY_SOURCE routines
>> on memcpy().
>>
>> [1] https://en.wikipedia.org/wiki/Flexible_array_member
>> [2] https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>>
>> Link: https://github.com/KSPP/linux/issues/78
>> Link: https://github.com/KSPP/linux/issues/180
>> Suggested-by: Gustavo A. R. Silva <gustavoars@...nel.org>
>> Signed-off-by: Stephen Kitt <steve@....org>
> 
> Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks for the patch

Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>

I just realized we have additional cases in this directory (interface
between kernel and firmware), I'll send a follow-up patch a

channel_map.h:  int32_t ch_coeffs[0];
channel_map.h:  struct sof_ipc_channel_map ch_map[0];
control.h:              struct sof_ipc_ctrl_value_chan chanv[0];
control.h:              struct sof_ipc_ctrl_value_comp compv[0];
control.h:              struct sof_abi_hdr data[0];
control.h:              struct sof_abi_hdr data[0];

> 
> Thanks!
> --
> Gustavo
> 
>> ---
>>  include/sound/sof/topology.h | 2 +-
>>  sound/soc/sof/topology.c     | 2 +-
>>  2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/sound/sof/topology.h b/include/sound/sof/topology.h
>> index d12736e14b69..adee6afd1490 100644
>> --- a/include/sound/sof/topology.h
>> +++ b/include/sound/sof/topology.h
>> @@ -237,7 +237,7 @@ struct sof_ipc_comp_process {
>>  	/* reserved for future use */
>>  	uint32_t reserved[7];
>>  
>> -	uint8_t data[0];
>> +	uint8_t data[];
>>  } __packed;
>>  
>>  /* frees components, buffers and pipelines
>> diff --git a/sound/soc/sof/topology.c b/sound/soc/sof/topology.c
>> index e72dcae5e7ee..1d119d1dd69d 100644
>> --- a/sound/soc/sof/topology.c
>> +++ b/sound/soc/sof/topology.c
>> @@ -2164,7 +2164,7 @@ static int sof_process_load(struct snd_soc_component *scomp, int index,
>>  	 */
>>  	if (ipc_data_size) {
>>  		for (i = 0; i < widget->num_kcontrols; i++) {
>> -			memcpy(&process->data + offset,
>> +			memcpy(&process->data[offset],
>>  			       wdata[i].pdata->data,
>>  			       wdata[i].pdata->size);
>>  			offset += wdata[i].pdata->size;
>>
>> base-commit: f71077a4d84bbe8c7b91b7db7c4ef815755ac5e3
>> -- 
>> 2.27.0
>>