linux-kernel - Re: [PATCH] ASoC: dapm: fix bounds checker error in dapm_widget_list

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Message-ID: <c9002b28-77a9-4be0-94a6-bf700e0abaab@linux.intel.com>
Date: Tue, 29 Oct 2024 13:11:32 +0100
From: Amadeusz Sławiński
 <amadeuszx.slawinski@...ux.intel.com>
To: Takashi Iwai <tiwai@...e.de>
Cc: Aleksei Vetrov <vvvvvv@...gle.com>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
 Takashi Iwai <tiwai@...e.com>, Kees Cook <kees@...nel.org>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, linux-sound@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ASoC: dapm: fix bounds checker error in
 dapm_widget_list_create

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@...gle.com>
>>> ---
>>>    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.