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

[Christophe JAILLET]

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@xxxxxxxxxx>
> > ---
> > 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);