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

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Date: Wed, 14 Feb 2024 12:37:47 +0100
From: Takashi Iwai <tiwai@...e.de>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Aiswarya Cyriac <Aiswarya.Cyriac@...nsynergy.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	"perex@...ex.cz" <perex@...ex.cz>,
	"tiwai@...e.com" <tiwai@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"virtualization@...ts.linux-foundation.org" <virtualization@...ts.linux-foundation.org>,
	"virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
	Anton Yakovlev <Anton.Yakovlev@...nsynergy.com>,
	coverity-bot <keescook+coverity-bot@...omium.org>,
	Mikhail Golubev-Ciuchea <Mikhail.Golubev-Ciuchea@...nsynergy.com>
Subject: Re: [PATCH] ALSA: virtio: Fix "Coverity: virtsnd_kctl_tlv_op(): Uninitialized variables" warning.

On Wed, 14 Feb 2024 12:30:19 +0100,
Michael S. Tsirkin wrote:
> 
> On Wed, Feb 14, 2024 at 09:08:26AM +0000, Aiswarya Cyriac wrote:
> > 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@...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.
> > 
> > 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.
> 
> Well we don't normally have functions validate inputs.
> In this case I am not really sure we should bother
> with adding dead code. If you really want to, add BUG_ON.

Please don't use BUG_ON() in such a case...
There is no reason to break the whole operation.


thanks,

Takashi