ASoC: SOF: ipc4-topology: Use size_t for variable passed to kzalloc()

  struct_size() checks for overflow, but assigning its result to just a u32
may still overflow after a successful check.

Use a size_t instead in order to be cleaner.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
---
Based on analysis from Dan Carpenter on another patch (see [1]).

[1]: https://lore.kernel.org/all/00e84595-e2c9-48ea-8737-18da34eaafbf@kili.mountain/
---
 sound/soc/sof/ipc4-topology.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
  

On 6/1/23 12:30, Christophe JAILLET wrote:
> struct_size() checks for overflow, but assigning its result to just a u32
> may still overflow after a successful check.
> 
> Use a size_t instead in order to be cleaner.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> Based on analysis from Dan Carpenter on another patch (see [1]).
> 
> [1]: https://lore.kernel.org/all/00e84595-e2c9-48ea-8737-18da34eaafbf@kili.mountain/

looks like there are similar cases of struct_size -> u32 conversions in
other places:

struct snd_sof_control {
    u32 size;	/* cdata size */

ipc3-topology.c:        scontrol->size = struct_size(cdata, chanv,
scontrol->num_channels);
ipc3-topology.c:        scontrol->size = struct_size(cdata, chanv,
scontrol->num_channels);
ipc4-topology.c:        scontrol->size = struct_size(control_data,
chanv, scontrol->num_channels);

not sure how much of an issue this really is though?

> ---
>  sound/soc/sof/ipc4-topology.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/soc/sof/ipc4-topology.c b/sound/soc/sof/ipc4-topology.c
> index db64e0cb8663..50faa4c88b97 100644
> --- a/sound/soc/sof/ipc4-topology.c
> +++ b/sound/soc/sof/ipc4-topology.c
> @@ -881,7 +881,7 @@ static int sof_ipc4_widget_setup_comp_process(struct snd_sof_widget *swidget)
>  	/* allocate memory for base config extension if needed */
>  	if (process->init_config == SOF_IPC4_MODULE_INIT_CONFIG_TYPE_BASE_CFG_WITH_EXT) {
>  		struct sof_ipc4_base_module_cfg_ext *base_cfg_ext;
> -		u32 ext_size = struct_size(base_cfg_ext, pin_formats,
> +		size_t ext_size = struct_size(base_cfg_ext, pin_formats,
>  						swidget->num_input_pins + swidget->num_output_pins);
>  
>  		base_cfg_ext = kzalloc(ext_size, GFP_KERNEL);
  

Le 01/06/2023 à 19:39, Pierre-Louis Bossart a écrit :
> 
> 
> On 6/1/23 12:30, Christophe JAILLET wrote:
>> struct_size() checks for overflow, but assigning its result to just a u32
>> may still overflow after a successful check.
>>
>> Use a size_t instead in order to be cleaner.
>>
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
>> ---
>> Based on analysis from Dan Carpenter on another patch (see [1]).
>>
>> [1]: https://lore.kernel.org/all/00e84595-e2c9-48ea-8737-18da34eaafbf@kili.mountain/
> 
> looks like there are similar cases of struct_size -> u32 conversions in
> other places:
> 
> struct snd_sof_control {
>      u32 size;	/* cdata size */
> 
> ipc3-topology.c:        scontrol->size = struct_size(cdata, chanv,
> scontrol->num_channels);
> ipc3-topology.c:        scontrol->size = struct_size(cdata, chanv,
> scontrol->num_channels);
> ipc4-topology.c:        scontrol->size = struct_size(control_data,
> chanv, scontrol->num_channels);

My coccinelle script does not handle such cases.

> 
> not sure how much of an issue this really is though?

I agree that in practice it should be safe as-is, but it can't hurt :).
I don't know this code well, but should [2] be part of the call chain, 
it is obvious that it CAN'T overflow.


I checked for places where such pattern occurs after Dan's comment on 
another patch. I'll see if I find better candidates.


CJ

[2]: 
https://elixir.bootlin.com/linux/v6.4-rc1/source/sound/soc/sof/topology.c#L1404

> 
>> ---
>>   sound/soc/sof/ipc4-topology.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/sound/soc/sof/ipc4-topology.c b/sound/soc/sof/ipc4-topology.c
>> index db64e0cb8663..50faa4c88b97 100644
>> --- a/sound/soc/sof/ipc4-topology.c
>> +++ b/sound/soc/sof/ipc4-topology.c
>> @@ -881,7 +881,7 @@ static int sof_ipc4_widget_setup_comp_process(struct snd_sof_widget *swidget)
>>   	/* allocate memory for base config extension if needed */
>>   	if (process->init_config == SOF_IPC4_MODULE_INIT_CONFIG_TYPE_BASE_CFG_WITH_EXT) {
>>   		struct sof_ipc4_base_module_cfg_ext *base_cfg_ext;
>> -		u32 ext_size = struct_size(base_cfg_ext, pin_formats,
>> +		size_t ext_size = struct_size(base_cfg_ext, pin_formats,
>>   						swidget->num_input_pins + swidget->num_output_pins);
>>   
>>   		base_cfg_ext = kzalloc(ext_size, GFP_KERNEL);
>
  

On Thu, Jun 01, 2023 at 07:30:12PM +0200, Christophe JAILLET wrote:
> struct_size() checks for overflow, but assigning its result to just a u32
> may still overflow after a successful check.
> 
> Use a size_t instead in order to be cleaner.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
> ---
> Based on analysis from Dan Carpenter on another patch (see [1]).
> 
> [1]: https://lore.kernel.org/all/00e84595-e2c9-48ea-8737-18da34eaafbf@kili.mountain/
> ---
>  sound/soc/sof/ipc4-topology.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/soc/sof/ipc4-topology.c b/sound/soc/sof/ipc4-topology.c
> index db64e0cb8663..50faa4c88b97 100644
> --- a/sound/soc/sof/ipc4-topology.c
> +++ b/sound/soc/sof/ipc4-topology.c
> @@ -881,7 +881,7 @@ static int sof_ipc4_widget_setup_comp_process(struct snd_sof_widget *swidget)
>  	/* allocate memory for base config extension if needed */
>  	if (process->init_config == SOF_IPC4_MODULE_INIT_CONFIG_TYPE_BASE_CFG_WITH_EXT) {
>  		struct sof_ipc4_base_module_cfg_ext *base_cfg_ext;
> -		u32 ext_size = struct_size(base_cfg_ext, pin_formats,
> +		size_t ext_size = struct_size(base_cfg_ext, pin_formats,
>  						swidget->num_input_pins + swidget->num_output_pins);

The temptation would be to change the addition as well:

	size_t ext_size = struct_size(base_cfg_ext, pin_formats,
				      size_add(swidget->num_input_pins, swidget->num_output_pins);

These values can only be in the 0-8 range so it's not a real bug.

Smatch cannot parse this data correctly to verify that it is safe.
Maybe in two years Smatch will be able to.  Probably a human who is
unfamiliar with this code can figure out that it is safe within 15
minutes?

I think the change to size_t doesn't hurt anyone and there isn't any
downside to it.  The size_add() change is slightly less readable than
just adding the numbers but I think eventually people will just get used
to it.

regards,
dan carpenter