Re: [PATCH] ALSA: virtio: Fix "Coverity: virtsnd_kctl_tlv_op(): Uninitialized variables" warning.

[Aiswarya Cyriac]

Hi Michael,

Thank you for reviewing. I have updated my response inline

On Tue, Feb 13, 2024 at 09:51:30AM +0100, Aiswarya Cyriac wrote:
>> Fix the following warning when building virtio_snd driver.
>>
>> "
>> *** CID 1583619:  Uninitialized variables  (UNINIT)
>> sound/virtio/virtio_kctl.c:294 in virtsnd_kctl_tlv_op()
>> 288
>> 289         break;
>> 290       }
>> 291
>> 292       kfree(tlv);
>> 293
>> vvv     CID 1583619:  Uninitialized variables  (UNINIT)
>> vvv     Using uninitialized value "rc".
>> 294       return rc;
>> 295     }
>> 296
>> 297     /**
>> 298      * virtsnd_kctl_get_enum_items() - Query items for the ENUMERATED element type.
>> 299      * @snd: VirtIO sound device.
>> "
>>
>> Signed-off-by: Anton Yakovlev <anton.yakovlev@xxxxxxxxxxxxxxx>
>> Signed-off-by: Aiswarya Cyriac <aiswarya.cyriac@xxxxxxxxxxxxxxx>
>> Reported-by: coverity-bot <keescook+coverity-bot@xxxxxxxxxxxx>
>> Addresses-Coverity-ID: 1583619 ("Uninitialized variables")
>> Fixes: d6568e3de42d ("ALSA: virtio: add support for audio controls")

>I don't know enough about ALSA to say whether the patch is correct.  But
>the commit log needs work: please, do not "fix warnings" - analyse the
>code and explain whether there is a real issue and if yes what is it
>and how it can trigger. Is an invalid op_flag ever passed?
>If it's just a coverity false positive it might be ok to
>work around that but document this.

This warning is caused by the absence of the "default" branch in the
switch-block, and is a false positive because the kernel calls
virtsnd_kctl_tlv_op() only with values for op_flag processed in
this block.
I will update the fix and send a v2 patch

>> ---
>>  sound/virtio/virtio_kctl.c | 5 +++++
>>  1 file changed, 5 insertions(+)
>>
>> diff --git a/sound/virtio/virtio_kctl.c b/sound/virtio/virtio_kctl.c
>> index 0c6ac74aca1e..d7a160c5db03 100644
>> --- a/sound/virtio/virtio_kctl.c
>> +++ b/sound/virtio/virtio_kctl.c
>> @@ -286,6 +286,11 @@ static int virtsnd_kctl_tlv_op(struct snd_kcontrol *kcontrol, int op_flag,
>>                else
>>                        rc = virtsnd_ctl_msg_send(snd, msg, &sg, NULL, false);
>>
>> +             break;
>> +     default:
>> +             virtsnd_ctl_msg_unref(msg);
>> +             rc = -EINVAL;
>> +

>There's already virtsnd_ctl_msg_unref call above.
>Also don't we need virtsnd_ctl_msg_unref on other error paths
>such as EFAULT?
>Unify error handling to fix it all then?

This also need to be handled and virtsnd_ctl_msg_unref needed in case of EFAULT as well.
I will update the patch.


Thanks,
Aiswarya Cyriac
Software Engineer
​
OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin

EMail: aiswarya.cyriac@xxxxxxxxxxxxxxx

www.opensynergy.com
Handelsregister/Commercial Registry: Amtsgericht Charlottenburg, HRB 108616B
Geschäftsführer/Managing Director: Régis Adjamah

________________________________________
From: Michael S. Tsirkin <mst@xxxxxxxxxx>
Sent: Tuesday, February 13, 2024 10:06 AM
To: Aiswarya Cyriac
Cc: jasowang@xxxxxxxxxx; perex@xxxxxxxx; tiwai@xxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; alsa-devel@xxxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; virtio-dev@xxxxxxxxxxxxxxxxxxxx; Anton Yakovlev; coverity-bot
Subject: Re: [PATCH] ALSA: virtio: Fix "Coverity: virtsnd_kctl_tlv_op(): Uninitialized variables" warning.

On Tue, Feb 13, 2024 at 09:51:30AM +0100, Aiswarya Cyriac wrote:
> Fix the following warning when building virtio_snd driver.
>
> "
> *** CID 1583619:  Uninitialized variables  (UNINIT)
> sound/virtio/virtio_kctl.c:294 in virtsnd_kctl_tlv_op()
> 288
> 289         break;
> 290       }
> 291
> 292       kfree(tlv);
> 293
> vvv     CID 1583619:  Uninitialized variables  (UNINIT)
> vvv     Using uninitialized value "rc".
> 294       return rc;
> 295     }
> 296
> 297     /**
> 298      * virtsnd_kctl_get_enum_items() - Query items for the ENUMERATED element type.
> 299      * @snd: VirtIO sound device.
> "
>
> Signed-off-by: Anton Yakovlev <anton.yakovlev@xxxxxxxxxxxxxxx>
> Signed-off-by: Aiswarya Cyriac <aiswarya.cyriac@xxxxxxxxxxxxxxx>
> Reported-by: coverity-bot <keescook+coverity-bot@xxxxxxxxxxxx>
> Addresses-Coverity-ID: 1583619 ("Uninitialized variables")
> Fixes: d6568e3de42d ("ALSA: virtio: add support for audio controls")

I don't know enough about ALSA to say whether the patch is correct.  But
the commit log needs work: please, do not "fix warnings" - analyse the
code and explain whether there is a real issue and if yes what is it
and how it can trigger. Is an invalid op_flag ever passed?
If it's just a coverity false positive it might be ok to
work around that but document this.


> ---
>  sound/virtio/virtio_kctl.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/sound/virtio/virtio_kctl.c b/sound/virtio/virtio_kctl.c
> index 0c6ac74aca1e..d7a160c5db03 100644
> --- a/sound/virtio/virtio_kctl.c
> +++ b/sound/virtio/virtio_kctl.c
> @@ -286,6 +286,11 @@ static int virtsnd_kctl_tlv_op(struct snd_kcontrol *kcontrol, int op_flag,
>               else
>                       rc = virtsnd_ctl_msg_send(snd, msg, &sg, NULL, false);
>
> +             break;
> +     default:
> +             virtsnd_ctl_msg_unref(msg);
> +             rc = -EINVAL;
> +

There's already virtsnd_ctl_msg_unref call above.
Also don't we need virtsnd_ctl_msg_unref on other error paths
such as EFAULT?
Unify error handling to fix it all then?

>               break;
>       }
>
> --
> 2.43.0