There are several ways that VMs can take advantage of UFO and get the host to do fragmentation for them:
drivers/net/macvtap.c: gso_type = SKB_GSO_UDP;
drivers/net/tun.c: skb_shinfo(skb)->gso_type = SKB_GSO_UDP;
drivers/net/virtio_net.c: skb_shinfo(skb)->gso_type =
SKB_GSO_UDP;
Our implementation of UFO for IPv6 does:
fptr = (struct frag_hdr *)(skb_network_header(skb) +
unfrag_ip6hlen);
fptr->nexthdr = nexthdr;
fptr->reserved = 0;
fptr->identification = skb_shinfo(skb)->ip6_frag_id;
which assumes ip6_frag_id has been set. That's only true if the local
stack constructed the skb; otherwise it appears we get zero.
This seems to be a regression as a result of:
commit 916e4cf46d0204806c062c8c6c4d1f633852c5b6
Author: Hannes Frederic Sowa <[email protected]>
Date: Fri Feb 21 02:55:35 2014 +0100
ipv6: reuse ip6_frag_id from ip6_ufo_append_data
However, that change seems reasonable - we *shouldn't* be choosing IDs
for any other stack. Any paravirt net driver that can use IPv6 UFO
needs to have some way of passing a fragmentation ID to put in
skb_shared_info::ip6_frag_id.
Ben.
--
Ben Hutchings
For every action, there is an equal and opposite criticism. - Harrison
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