Re: [v4 PATCH] ALSA: virtio: Fix "Coverity: virtsnd_kctl_tlv_op(): Uninitialized variables" warning.

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Feb 16, 2024 at 11:06:43AM +0100, Aiswarya Cyriac wrote:
> This commit fixes 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.
> "
> 
> 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.
> 
> Also, this commit unifies the cleanup path for all possible control
> paths in the callback function.
> 
> Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
> Signed-off-by: Aiswarya Cyriac <aiswarya.cyriac@opensynergy.com>
> Reported-by: coverity-bot <keescook+coverity-bot@chromium.org>
> Addresses-Coverity-ID: 1583619 ("Uninitialized variables")
> Fixes: d6568e3de42d ("ALSA: virtio: add support for audio controls")



> ---
>  sound/virtio/virtio_kctl.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/sound/virtio/virtio_kctl.c b/sound/virtio/virtio_kctl.c
> index 0c6ac74aca1e..7aa79c05b464 100644
> --- a/sound/virtio/virtio_kctl.c
> +++ b/sound/virtio/virtio_kctl.c
> @@ -253,8 +253,8 @@ static int virtsnd_kctl_tlv_op(struct snd_kcontrol *kcontrol, int op_flag,
>  
>  	tlv = kzalloc(size, GFP_KERNEL);
>  	if (!tlv) {
> -		virtsnd_ctl_msg_unref(msg);
> -		return -ENOMEM;
> +		rc = -ENOMEM;
> +		goto on_msg_unref;
>  	}
>  
>  	sg_init_one(&sg, tlv, size);
> @@ -281,14 +281,25 @@ static int virtsnd_kctl_tlv_op(struct snd_kcontrol *kcontrol, int op_flag,
>  			hdr->hdr.code =
>  				cpu_to_le32(VIRTIO_SND_R_CTL_TLV_COMMAND);
>  
> -		if (copy_from_user(tlv, utlv, size))
> +		if (copy_from_user(tlv, utlv, size)) {
>  			rc = -EFAULT;
> -		else
> +			goto on_msg_unref;
> +		} else {
>  			rc = virtsnd_ctl_msg_send(snd, msg, &sg, NULL, false);
> +		}
>  
>  		break;
> +	default:
> +		rc = -EINVAL;
> +		/* We never get here - we listed all values for op_flag */
> +		WARN_ON(1);
> +		goto on_msg_unref;
>  	}
> +	kfree(tlv);
> +	return rc;
>  
> +on_msg_unref:
> +	virtsnd_ctl_msg_unref(msg);
>  	kfree(tlv);
>  
>  	return rc;

I don't really like adding code for a false-positive but ALSA
maintainers seem to like this. If yes, this seems like as good
a way as any to do it.

Acked-by: Michael S. Tsirkin <mst@redhat.com>


> -- 
> 2.43.2