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

Michael S. Tsirkin
2024-02-16T11:27:56Z

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