Re: [PATCH] ASoC: SOF: ipc4-topology: Use size_t for variable passed to kzalloc()

[Dan Carpenter <dan.carpenter@linaro.org>]

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