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SubjectRe: [PATCH RFC 2/4] vhost/vsock: split packets to send using multiple buffers
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).

> - 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.
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