Re: [PATCH net-next v2 6/9] xen-netback: Handle guests with too manyfrags

[Zoltan Kiss]

On 16/12/13 18:09, Wei Liu wrote:
> > > > diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
> > > > index e26cdda..f6ed1c8 100644
> > > > --- a/drivers/net/xen-netback/netback.c
> > > > +++ b/drivers/net/xen-netback/netback.c
> > > > @@ -906,11 +906,15 @@ static struct gnttab_map_grant_ref *xenvif_get_requests(struct xenvif *vif,
> > > >   	u16 pending_idx = *((u16 *)skb->data);
> > > >   	int start;
> > > >   	pending_ring_idx_t index;
> > > > -	unsigned int nr_slots;
> > > > +	unsigned int nr_slots, frag_overflow = 0;
> > > >
> > > >   	/* At this point shinfo->nr_frags is in fact the number of
> > > >   	 * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
> > > >   	 */
> > > > +	if (shinfo->nr_frags > MAX_SKB_FRAGS) {
> > > > +		frag_overflow = shinfo->nr_frags - MAX_SKB_FRAGS;
> > > > +		shinfo->nr_frags = MAX_SKB_FRAGS;
> > > > +	}
> > > >   	nr_slots = shinfo->nr_frags;
> > >
> > > It is also probably better to check whether shinfo->nr_frags is too
> > > large which makes frag_overflow > MAX_SKB_FRAGS. I know skb should be
> > > already be valid at this point but it wouldn't hurt to be more careful.
> > Ok, I've added this:
> > 	/* At this point shinfo->nr_frags is in fact the number of
> > 	 * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
> > 	 */
> > +	if (shinfo->nr_frags > MAX_SKB_FRAGS) {
> > +		if (shinfo->nr_frags > XEN_NETBK_LEGACY_SLOTS_MAX) return NULL;
> > +		frag_overflow = shinfo->nr_frags - MAX_SKB_FRAGS;
>
> What I suggested is
>
>     BUG_ON(frag_overflow > MAX_SKB_FRAGS)

Ok, I've changed it.

Zoli

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