Re: [PATCH] virtio_ring : fix vring_packed_desc memory out of bounds bug

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

On Mon, Jun 13, 2022 at 02:56:19PM +0800, Jason Wang wrote:
> On Fri, Jun 10, 2022 at 10:51 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Fri, Jun 10, 2022 at 06:33:14PM +0800, huangjie.albert wrote:
> > > ksoftirqd may consume the packet and it will call:
> > > virtnet_poll
> > >       -->virtnet_receive
> > >               -->virtqueue_get_buf_ctx
> > >                       -->virtqueue_get_buf_ctx_packed
> > > and in virtqueue_get_buf_ctx_packed:
> > >
> > > vq->last_used_idx += vq->packed.desc_state[id].num;
> > > if (unlikely(vq->last_used_idx >= vq->packed.vring.num)) {
> > >          vq->last_used_idx -= vq->packed.vring.num;
> > >          vq->packed.used_wrap_counter ^= 1;
> > > }
> > >
> > > if at the same time, there comes a vring interrupt，in vring_interrupt:
> > > we will call:
> > > vring_interrupt
> > >       -->more_used
> > >               -->more_used_packed
> > >                       -->is_used_desc_packed
> > > in is_used_desc_packed, the last_used_idx maybe >= vq->packed.vring.num.
> > > so this could case a memory out of bounds bug.
> > >
> > > this patch is to fix this.
> > >
> > > Signed-off-by: huangjie.albert <huangjie.albert@bytedance.com>
> >
> >
> > This pattern was always iffy, but I don't think the patch
> > improves the situation much. last_used_idx and vq->packed.used_wrap_counter
> > can still get out of sync.
> >
> > Maybe refactor code to keep everything in vq->last_used_idx?
> >
> > Jason what is your take?
> 
> I think we can do this since 16bit/32bit operations are guaranteed to be atomic.
> 
> Thanks


OK. Who's working on this?

> >
> >
> >
> >
> >
> > > ---
> > >  drivers/virtio/virtio_ring.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> > > index 13a7348cedff..d2abbb3a8187 100644
> > > --- a/drivers/virtio/virtio_ring.c
> > > +++ b/drivers/virtio/virtio_ring.c
> > > @@ -1397,6 +1397,9 @@ static inline bool is_used_desc_packed(const struct vring_virtqueue *vq,
> > >       bool avail, used;
> > >       u16 flags;
> > >
> > > +     if (idx >= vq->packed.vring.num)
> > > +             return false;
> > > +
> > >       flags = le16_to_cpu(vq->packed.vring.desc[idx].flags);
> > >       avail = !!(flags & (1 << VRING_PACKED_DESC_F_AVAIL));
> > >       used = !!(flags & (1 << VRING_PACKED_DESC_F_USED));
> > > --
> > > 2.27.0
> >

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