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

[Michael S. Tsirkin]

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@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.

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.



> 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
> 
>