On Fri, Aug 19, 2016 at 10:09 AM, David Ahern <d...@cumulusnetworks.com> wrote:
> As reported by Lennert the MPLS GSO code is failing to properly segment
> large packets. There are a couple of problems:
>
> 1. the inner protocol is not set so the gso segment functions for inner
> protocol layers are not getting run, and
>
> 2 MPLS labels for packets that use the "native" (non-OVS) MPLS code
> are not properly accounted for in mpls_gso_segment.
>
> The MPLS GSO code was added for OVS. It is re-using skb_mac_gso_segment
> to call the gso segment functions for the higher layer protocols. That
> means skb_mac_gso_segment is called twice -- once with the network
> protocol set to MPLS and again with the network protocol set to the
> inner protocol.
>
> This patch sets the inner skb protocol addressing item 1 above and sets
> the network_header and inner_network_header to mark where the MPLS labels
> start and end. The MPLS code in OVS is also updated to set the two
> network markers.
>
> From there the MPLS GSO code uses the difference between the network
> header and the inner network header to know the size of the MPLS header
> that was pushed. It then pulls the MPLS header, resets the mac_len and
> protocol for the inner protocol and then calls skb_mac_gso_segment
> to segment the skb.
>
> Afterward the inner protocol segmentation is done the skb protocol
> is set to mpls for each segment and the network and mac headers
> restored.
>
> Reported-by: Lennert Buytenhek <buyt...@wantstofly.org>
> Signed-off-by: David Ahern <d...@cumulusnetworks.com>
> ---
> net/mpls/mpls_gso.c | 38 +++++++++++++++++++++++++++-----------
> net/mpls/mpls_iptunnel.c | 4 ++++
> net/openvswitch/actions.c | 6 ++++++
> 3 files changed, 37 insertions(+), 11 deletions(-)
>
> diff --git a/net/mpls/mpls_gso.c b/net/mpls/mpls_gso.c
> index 2055e57ed1c3..2aa4beaa0e4f 100644
> --- a/net/mpls/mpls_gso.c
> +++ b/net/mpls/mpls_gso.c
> @@ -23,32 +23,48 @@ static struct sk_buff *mpls_gso_segment(struct sk_buff
> *skb,
> netdev_features_t features)
> {
> struct sk_buff *segs = ERR_PTR(-EINVAL);
> + u16 mac_offset = skb->mac_header;
> netdev_features_t mpls_features;
> + u16 mac_len = skb->mac_len;
> __be16 mpls_protocol;
> + int mpls_hlen;
> +
> + skb_reset_network_header(skb);
> + mpls_hlen = skb_inner_network_header(skb) - skb_network_header(skb);
> + if (unlikely(!pskb_may_pull(skb, mpls_hlen)))
> + goto out;
>
> /* Setup inner SKB. */
> mpls_protocol = skb->protocol;
> skb->protocol = skb->inner_protocol;
>
> - /* Push back the mac header that skb_mac_gso_segment() has pulled.
> - * It will be re-pulled by the call to skb_mac_gso_segment() below
> - */
> - __skb_push(skb, skb->mac_len);
> + __skb_pull(skb, mpls_hlen);
> +
> + skb->mac_len = 0;
> + skb_reset_mac_header(skb);
> + skb_set_network_header(skb, skb_inner_network_offset(skb));
No need to set the network header. Both IPv4 and IPv6 GSO paths will
reset the network header just like you did at the start.
> /* Segment inner packet. */
> mpls_features = skb->dev->mpls_features & features;
> segs = skb_mac_gso_segment(skb, mpls_features);
> + if (IS_ERR_OR_NULL(segs)) {
> + skb_gso_error_unwind(skb, mpls_protocol, mpls_hlen,
> mac_offset,
> + mac_len);
> + goto out;
> + }
>
> + skb = segs;
You could probably pull your math for mpls_hlen + mac_len out of the
loop below and just take care of adding mac_len to mpls_hlen up here
and store it of in mpls_hlen since it isn't used anywhere else.
> + do {
> + skb->mac_len = mac_len;
> + skb->protocol = mpls_protocol;
>
> - /* Restore outer protocol. */
> - skb->protocol = mpls_protocol;
> + __skb_push(skb, mpls_hlen + mac_len);
>
> - /* Re-pull the mac header that the call to skb_mac_gso_segment()
> - * above pulled. It will be re-pushed after returning
> - * skb_mac_gso_segment(), an indirect caller of this function.
> - */
> - __skb_pull(skb, skb->data - skb_mac_header(skb));
You need to store off the inner network header before you overwrite it
in the lines below. Either skb_reset_inner_network_header before the
push, or skb_reset_inner_headers before you call the two lines below.
> + skb_reset_mac_header(skb);
> + skb_set_network_header(skb, mac_len);
> + } while ((skb = skb->next));
>
> +out:
> return segs;
> }
>
> diff --git a/net/mpls/mpls_iptunnel.c b/net/mpls/mpls_iptunnel.c
> index aed872cc05a6..cf52cf30ac4b 100644
> --- a/net/mpls/mpls_iptunnel.c
> +++ b/net/mpls/mpls_iptunnel.c
> @@ -90,7 +90,11 @@ static int mpls_xmit(struct sk_buff *skb)
> if (skb_cow(skb, hh_len + new_header_size))
> goto drop;
>
> + skb_set_inner_protocol(skb, skb->protocol);
> + skb_reset_inner_network_header(skb);
> +
> skb_push(skb, new_header_size);
> +
> skb_reset_network_header(skb);
>
> skb->dev = out_dev;
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index 1ecbd7715f6d..6d78f162a88b 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -167,6 +167,12 @@ static int push_mpls(struct sk_buff *skb, struct
> sw_flow_key *key,
> skb->mac_len);
> skb_reset_mac_header(skb);
>
> + /* for GSO: set MPLS as network header and encapsulated protocol
> + * header as inner network header
> + */
> + skb_set_network_header(skb, skb->mac_len);
> + skb_set_inner_network_header(skb, skb->mac_len + MPLS_HLEN);
> +
> new_mpls_lse = (__be32 *)skb_mpls_header(skb);
> *new_mpls_lse = mpls->mpls_lse;
>
> --
> 2.1.4
>
