2023-06-15 02:57:38

by Su Hui

Subject: [PATCH] ALSA: ac97: Fix possible NULL dereference in snd_ac97_mixer

smatch error:
sound/pci/ac97/ac97_codec.c:2354 snd_ac97_mixer() error:
we previously assumed 'rac97' could be null (see line 2072)

remove redundant assignment, return error if rac97 is NULL.

Fixes: da3cec35dd3c ("ALSA: Kill snd_assert() in sound/pci/*")
Signed-off-by: Su Hui <[email protected]>
---
sound/pci/ac97/ac97_codec.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/pci/ac97/ac97_codec.c b/sound/pci/ac97/ac97_codec.c
index 9afc5906d662..80a65b8ad7b9 100644
--- a/sound/pci/ac97/ac97_codec.c
+++ b/sound/pci/ac97/ac97_codec.c
@@ -2069,8 +2069,8 @@ int snd_ac97_mixer(struct snd_ac97_bus *bus, struct snd_ac97_template *template,
.dev_disconnect = snd_ac97_dev_disconnect,
};

- if (rac97)
- *rac97 = NULL;
+ if (!rac97)
+ return -EINVAL;
if (snd_BUG_ON(!bus || !template))
return -EINVAL;
if (snd_BUG_ON(template->num >= 4))
--
2.30.2

2023-06-15 06:50:24

by Takashi Iwai

Subject: Re: [PATCH] ALSA: ac97: Fix possible NULL dereference in snd_ac97_mixer

On Thu, 15 Jun 2023 04:17:32 +0200,
Su Hui wrote:
>
> smatch error:
> sound/pci/ac97/ac97_codec.c:2354 snd_ac97_mixer() error:
> we previously assumed 'rac97' could be null (see line 2072)
>
> remove redundant assignment, return error if rac97 is NULL.
>
> Fixes: da3cec35dd3c ("ALSA: Kill snd_assert() in sound/pci/*")
> Signed-off-by: Su Hui <[email protected]>

Thanks, applied.


Takashi

2023-08-23 10:05:28

by Su Hui

Subject: Re: [PATCH] ALSA: ac97: Fix possible NULL dereference in snd_ac97_mixer

On 2023/8/23 04:07, Christophe JAILLET wrote:
> Le 15/06/2023 à 04:17, Su Hui a écrit :
>> smatch error:
>> sound/pci/ac97/ac97_codec.c:2354 snd_ac97_mixer() error:
>> we previously assumed 'rac97' could be null (see line 2072)
>>
>> remove redundant assignment, return error if rac97 is NULL.
>
> Hi,
>
> why is the assigment redundant?
>
> Should an error occur, the 'struct snd_ac97 **' parameter was garanted
> to be set to NULL, now it is left as-is.
>
> I've checked all callers and apparently this is fine because the
> probes fail if snd_ac97_mixer() returns an error.
>
> However, some drivers with several mixers seem to rely on the value
> being NULL in case of error.
>
> See [1] as an example of such code that forces a NULL value on its
> own, to be sure.
>
> So, wouldn't it be safer to leave a "*rac97 = NULL;" just after the
> added sanity check?
>
Hi,

Really thanks for pointing this mistake.

this assignment is necessary and removing it may cause some problem.

So sorry for my mistake, I will send a patch to fix it right now.

Su Hui

>
> CJ
>
>
> [1]:
> https://elixir.bootlin.com/linux/v6.5-rc7/source/sound/pci/atiixp.c#L1438
>
>>
>> Fixes: da3cec35dd3c ("ALSA: Kill snd_assert() in sound/pci/*")
>> Signed-off-by: Su Hui <[email protected]>
>> ---
>>   sound/pci/ac97/ac97_codec.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/sound/pci/ac97/ac97_codec.c b/sound/pci/ac97/ac97_codec.c
>> index 9afc5906d662..80a65b8ad7b9 100644
>> --- a/sound/pci/ac97/ac97_codec.c
>> +++ b/sound/pci/ac97/ac97_codec.c
>> @@ -2069,8 +2069,8 @@ int snd_ac97_mixer(struct snd_ac97_bus *bus,
>> struct snd_ac97_template *template,
>>           .dev_disconnect =    snd_ac97_dev_disconnect,
>>       };
>>   -    if (rac97)
>> -        *rac97 = NULL;
>> +    if (!rac97)
>> +        return -EINVAL;
>>       if (snd_BUG_ON(!bus || !template))
>>           return -EINVAL;
>>       if (snd_BUG_ON(template->num >= 4))
>