linux-kernel - Re: [PATCH] ALSA: virtio: Fix "Coverity: virtsnd_kctl_tlv

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Date: Tue, 13 Feb 2024 04:06:05 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Aiswarya Cyriac <aiswarya.cyriac@...nsynergy.com>
Cc: jasowang@...hat.com, perex@...ex.cz, tiwai@...e.com,
	linux-kernel@...r.kernel.org, alsa-devel@...a-project.org,
	virtualization@...ts.linux-foundation.org,
	virtio-dev@...ts.oasis-open.org,
	Anton Yakovlev <anton.yakovlev@...nsynergy.com>,
	coverity-bot <keescook+coverity-bot@...omium.org>
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@...nsynergy.com>
> Signed-off-by: Aiswarya Cyriac <aiswarya.cyriac@...nsynergy.com>
> Reported-by: coverity-bot <keescook+coverity-bot@...omium.org>
> 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