Re: [PATCH] ASoC: dapm: fix bounds checker error in dapm_widget_list_create

[Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>]

On 10/29/2024 11:30 AM, Takashi Iwai wrote:
> On Tue, 29 Oct 2024 10:50:21 +0100,
> Amadeusz Sławiński wrote:
> > On 10/28/2024 11:50 PM, Aleksei Vetrov wrote:
> > > The widgets array in the snd_soc_dapm_widget_list has a __counted_by
> > > attribute attached to it, which points to the num_widgets variable. This
> > > attribute is used in bounds checking, and if it is not set before the
> > > array is filled, then the bounds sanitizer will issue a warning or a
> > > kernel panic if CONFIG_UBSAN_TRAP is set.
> > >
> > > This patch sets the size of the widgets list calculated with
> > > list_for_each as the initial value for num_widgets as it is used for
> > > allocating memory for the array. It is updated with the actual number of
> > > added elements after the array is filled.
> > >
> > > Signed-off-by: Aleksei Vetrov <vvvvvv@xxxxxxxxxx>
> > > ---
> > >    sound/soc/soc-dapm.c | 2 ++
> > >    1 file changed, 2 insertions(+)
> > >
> > > diff --git a/sound/soc/soc-dapm.c b/sound/soc/soc-dapm.c
> > > index c34934c31ffec3970b34b24dcaa0826dfb7d8e86..99521c784a9b16a232a558029a2f3e88bd8ebfb1 100644
> > > --- a/sound/soc/soc-dapm.c
> > > +++ b/sound/soc/soc-dapm.c
> > > @@ -1147,6 +1147,8 @@ static int dapm_widget_list_create(struct snd_soc_dapm_widget_list **list,
> > >    	if (*list == NULL)
> > >    		return -ENOMEM;
> > >    +	(*list)->num_widgets = size;
> > > +
> > >    	list_for_each_entry(w, widgets, work_list)
> > >    		(*list)->widgets[i++] = w;
> > >    
> >
> > and after that there is (*list)->num_widgets = i;
> >
> > Can this be somehow simplified to remove 'i', if it set before assignment?
>
> That line can be removed after this change, I suppose.
> The size is calculated from the list at the beginning, and it must be
> the exact size.

Actually looking at this again, first iteration iterates through all 
widgets, while second one, only through work_list, which looks to me 
like it allocates more memory than needed in most cases.