Re: [PATCH v2] vringh: Fix loop descriptors check in the indirect cases

[Jason Wang <jasowang@redhat.com>]

On Tue, May 10, 2022 at 3:54 PM Yongji Xie <xieyongji@bytedance.com> wrote:
>
> On Tue, May 10, 2022 at 3:44 PM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Thu, May 5, 2022 at 6:08 PM Xie Yongji <xieyongji@bytedance.com> wrote:
> > >
> > > We should use size of descriptor chain to test loop condition
> > > in the indirect case. And another statistical count is also introduced
> > > for indirect descriptors to avoid conflict with the statistical count
> > > of direct descriptors.
> > >
> > > Fixes: f87d0fbb5798 ("vringh: host-side implementation of virtio rings.")
> > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > > Signed-off-by: Fam Zheng <fam.zheng@bytedance.com>
> > > ---
> > >  drivers/vhost/vringh.c | 10 ++++++++--
> > >  1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/vhost/vringh.c b/drivers/vhost/vringh.c
> > > index 14e2043d7685..eab55accf381 100644
> > > --- a/drivers/vhost/vringh.c
> > > +++ b/drivers/vhost/vringh.c
> > > @@ -292,7 +292,7 @@ __vringh_iov(struct vringh *vrh, u16 i,
> > >              int (*copy)(const struct vringh *vrh,
> > >                          void *dst, const void *src, size_t len))
> > >  {
> > > -       int err, count = 0, up_next, desc_max;
> > > +       int err, count = 0, indirect_count = 0, up_next, desc_max;
> > >         struct vring_desc desc, *descs;
> > >         struct vringh_range range = { -1ULL, 0 }, slowrange;
> > >         bool slow = false;
> > > @@ -349,7 +349,12 @@ __vringh_iov(struct vringh *vrh, u16 i,
> > >                         continue;
> > >                 }
> > >
> > > -               if (count++ == vrh->vring.num) {
> > > +               if (up_next == -1)
> > > +                       count++;
> > > +               else
> > > +                       indirect_count++;
> > > +
> > > +               if (count > vrh->vring.num || indirect_count > desc_max) {
> > >                         vringh_bad("Descriptor loop in %p", descs);
> > >                         err = -ELOOP;
> > >                         goto fail;
> > > @@ -411,6 +416,7 @@ __vringh_iov(struct vringh *vrh, u16 i,
> > >                                 i = return_from_indirect(vrh, &up_next,
> > >                                                          &descs, &desc_max);
> > >                                 slow = false;
> > > +                               indirect_count = 0;
> >
> > Do we need to reset up_next to -1 here?
> >
>
> It will be reset to -1 in return_from_indirect().

Right. Then

Acked-by: Jason Wang <jasowang@redhat.com>

Thanks

>
> Thanks,
> Yongji
>

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