[PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

[PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

[Gautam Dawar]

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When qemu with vhost-vdpa netdevice is run for the first time, it works
well.
But after the VM is powered off, the next qemu run causes kernel panic due
to
a NULL pointer dereference in irq_bypass_register_producer().

When the VM is powered off, vhost_vdpa_clean_irq() misses on calling
irq_bypass_unregister_producer() for irq 0 because of the existing check.

This leaves stale producer nodes, which are reset in
vhost_vring_call_reset()
when vhost_dev_init() is invoked during the second qemu run.

As the node member of struct irq_bypass_producer is also initialized
to zero, traversal on the producers list causes crash due to NULL pointer
dereference.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711
Signed-off-by: Gautam Dawar <gdawar@xilinx.com>


diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
index 62a9bb0efc55..d1c3a33c6239 100644
--- a/drivers/vhost/vdpa.c
+++ b/drivers/vhost/vdpa.c
@@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)

        for (i = 0; i < v->nvqs; i++) {
                vq = &v->vqs[i];
-               if (vq->call_ctx.producer.irq)
+               if (vq->call_ctx.producer.irq >= 0)

irq_bypass_unregister_producer(&vq->call_ctx.producer);
        }
 }

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Re: [PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

[Jason Wang]

On 2021/2/22 下午5:13, Gautam Dawar wrote:
> When qemu with vhost-vdpa netdevice is run for the first time, it 
> works well.
> But after the VM is powered off, the next qemu run causes kernel panic 
> due to
> a NULL pointer dereference in irq_bypass_register_producer().
>
> When the VM is powered off, vhost_vdpa_clean_irq() misses on calling
> irq_bypass_unregister_producer() for irq 0 because of the existing check.
>
> This leaves stale producer nodes, which are reset in 
> vhost_vring_call_reset()
> when vhost_dev_init() is invoked during the second qemu run.
>
> As the node member of struct irq_bypass_producer is also initialized
> to zero, traversal on the producers list causes crash due to NULL pointer
> dereference.
>
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711
> Signed-off-by: Gautam Dawar <gdawar@xilinx.com <mailto:gdawar@xilinx.com>>
>
>
> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index 62a9bb0efc55..d1c3a33c6239 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa *v)
>
>         for (i = 0; i < v->nvqs; i++) {
>                 vq = &v->vqs[i];
> -               if (vq->call_ctx.producer.irq)
> +               if (vq->call_ctx.producer.irq >= 0)
> irq_bypass_unregister_producer(&vq->call_ctx.producer);


Since it's impossible to have an irq < 0 ( see 
vhost_vdap_setup_vq_irq()), I think we can simply remove the check above.

Then we can call vhost_vdpa_unsetup_vq_irq() here to avoid temporary 
variable like vq.

Thanks


>         }
>  }

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Re: [PATCH] vhost vdpa: fix the irq check for invoking irq_bypass_unregister_producer

[Gautam Dawar]

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On Tue, 23 Feb 2021 at 10:13, Jason Wang <jasowang@redhat.com> wrote:

>
> On 2021/2/22 下午5:13, Gautam Dawar wrote:
> > When qemu with vhost-vdpa netdevice is run for the first time, it
> > works well.
> > But after the VM is powered off, the next qemu run causes kernel panic
> > due to
> > a NULL pointer dereference in irq_bypass_register_producer().
> >
> > When the VM is powered off, vhost_vdpa_clean_irq() misses on calling
> > irq_bypass_unregister_producer() for irq 0 because of the existing check.
> >
> > This leaves stale producer nodes, which are reset in
> > vhost_vring_call_reset()
> > when vhost_dev_init() is invoked during the second qemu run.
> >
> > As the node member of struct irq_bypass_producer is also initialized
> > to zero, traversal on the producers list causes crash due to NULL pointer
> > dereference.
> >
> > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211711
> > Signed-off-by: Gautam Dawar <gdawar@xilinx.com <mailto:gdawar@xilinx.com
> >>
> >
> >
> > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > index 62a9bb0efc55..d1c3a33c6239 100644
> > --- a/drivers/vhost/vdpa.c
> > +++ b/drivers/vhost/vdpa.c
> > @@ -849,7 +849,7 @@ static void vhost_vdpa_clean_irq(struct vhost_vdpa
> *v)
> >
> >         for (i = 0; i < v->nvqs; i++) {
> >                 vq = &v->vqs[i];
> > -               if (vq->call_ctx.producer.irq)
> > +               if (vq->call_ctx.producer.irq >= 0)
> > irq_bypass_unregister_producer(&vq->call_ctx.producer);
>
>
> Since it's impossible to have an irq < 0 ( see
> vhost_vdap_setup_vq_irq()), I think we can simply remove the check above.
>
> Then we can call vhost_vdpa_unsetup_vq_irq() here to avoid temporary
> variable like vq.
>
>
Done and submitted patch v2.


> Thanks
>
>
> >         }
> >  }
>
> Regards,
Gautam

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