Messages in this thread | | | Subject | Re: [PATCH net] net: virtio_net_hdr_to_skb: count transport header in UFO | From | Jonathan Davies <> | Date | Tue, 16 Nov 2021 17:43:05 +0000 |
| |
On 15/11/2021 16:34, Willem de Bruijn wrote: > On Mon, Nov 15, 2021 at 4:16 PM Jonathan Davies > <jonathan.davies@nutanix.com> wrote: >> >> virtio_net_hdr_to_skb does not set the skb's gso_size and gso_type >> correctly for UFO packets received via virtio-net that are a little over >> the GSO size. This can lead to problems elsewhere in the networking >> stack, e.g. ovs_vport_send dropping over-sized packets if gso_size is >> not set. >> >> This is due to the comparison >> >> if (skb->len - p_off > gso_size) >> >> not properly accounting for the transport layer header. >> >> p_off includes the size of the transport layer header (thlen), so >> skb->len - p_off is the size of the TCP/UDP payload. >> >> gso_size is read from the virtio-net header. For UFO, fragmentation >> happens at the IP level so does not need to include the UDP header. >> >> Hence the calculation could be comparing a TCP/UDP payload length with >> an IP payload length, causing legitimate virtio-net packets to have >> lack gso_type/gso_size information. >> >> Example: a UDP packet with payload size 1473 has IP payload size 1481. >> If the guest used UFO, it is not fragmented and the virtio-net header's >> flags indicate that it is a GSO frame (VIRTIO_NET_HDR_GSO_UDP), with >> gso_size = 1480 for an MTU of 1500. skb->len will be 1515 and p_off >> will be 42, so skb->len - p_off = 1473. Hence the comparison fails, and >> shinfo->gso_size and gso_type are not set as they should be. >> >> Instead, add the UDP header length before comparing to gso_size when >> using UFO. In this way, it is the size of the IP payload that is >> compared to gso_size. >> >> Fixes: 6dd912f8 ("net: check untrusted gso_size at kernel entry") >> Signed-off-by: Jonathan Davies <jonathan.davies@nutanix.com> > > Thanks for the fix, and the detailed explanation of the bug. > > Reviewed-by: Willem de Bruijn <willemb@google.com> > >> --- >> include/linux/virtio_net.h | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h >> index b465f8f..bea56af 100644 >> --- a/include/linux/virtio_net.h >> +++ b/include/linux/virtio_net.h >> @@ -122,8 +122,11 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, >> u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size); >> struct skb_shared_info *shinfo = skb_shinfo(skb); >> >> - /* Too small packets are not really GSO ones. */ >> - if (skb->len - p_off > gso_size) { >> + /* Too small packets are not really GSO ones. >> + * UFO may not include transport header in gso_size. >> + */ >> + if (gso_type & SKB_GSO_UDP && skb->len - p_off + thlen > gso_size || >> + skb->len - p_off > gso_size) { > > Perhaps for readability instead something like > > unsigned int nh_off = p_off; > > if (gso_type & SKB_GSO_UDP) > nh_off -= thlen;
Thanks for the suggestion. I agree that improves readability. v2 posted.
Jonathan
> > > > >> shinfo->gso_size = gso_size; >> shinfo->gso_type = gso_type; >> >> -- >> 2.9.3 >>
| |