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

[Takashi Iwai <tiwai@xxxxxxx>]

On Tue, 29 Oct 2024 13:11:32 +0100,
Amadeusz Sławiński wrote:
> 
> 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.

Oh, you're right.  I don't know why two different loops are used,
though...


Takashi