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SubjectRe: [PATCH RFC 2/4] vhost/vsock: split packets to send using multiple buffers
On Fri, Apr 05, 2019 at 09:13:56AM +0100, Stefan Hajnoczi wrote:
> On Thu, Apr 04, 2019 at 12:58:36PM +0200, Stefano Garzarella wrote:
> > @@ -139,8 +139,18 @@ vhost_transport_do_send_pkt(struct vhost_vsock *vsock,
> > break;
> > }
> >
> > - len = iov_length(&vq->iov[out], in);
> > - iov_iter_init(&iov_iter, READ, &vq->iov[out], in, len);
> > + payload_len = pkt->len - pkt->off;
> > + iov_len = iov_length(&vq->iov[out], in);
> > + iov_iter_init(&iov_iter, READ, &vq->iov[out], in, iov_len);
> > +
> > + /* If the packet is greater than the space available in the
> > + * buffer, we split it using multiple buffers.
> > + */
> > + if (payload_len > iov_len - sizeof(pkt->hdr))
>
> Integer underflow. iov_len is controlled by the guest and therefore
> untrusted. Please validate iov_len before assuming it's larger than
> sizeof(pkt->hdr).
>

Okay, I'll do it!

> > - vhost_add_used(vq, head, sizeof(pkt->hdr) + pkt->len);
> > + vhost_add_used(vq, head, sizeof(pkt->hdr) + payload_len);
> > added = true;
> >
> > + pkt->off += payload_len;
> > +
> > + /* If we didn't send all the payload we can requeue the packet
> > + * to send it with the next available buffer.
> > + */
> > + if (pkt->off < pkt->len) {
> > + spin_lock_bh(&vsock->send_pkt_list_lock);
> > + list_add(&pkt->list, &vsock->send_pkt_list);
> > + spin_unlock_bh(&vsock->send_pkt_list_lock);
> > + continue;
>
> The virtio_transport_deliver_tap_pkt() call is skipped. Packet capture
> should see the exact packets that are delivered. I think this patch
> will present one large packet instead of several smaller packets that
> were actually delivered.

I'll modify virtio_transport_build_skb() to take care of pkt->off
and reading the payload size from the virtio_vsock_hdr.
Otherwise, should I introduce another field in virtio_vsock_pkt to store
the payload size?

Thanks,
Stefano

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