path: root/net/ipv4/ip_tunnel_core.c
diff options
authorShmulik Ladkani <shmulik.ladkani@gmail.com>2016-07-18 14:49:34 +0300
committerDavid S. Miller <davem@davemloft.net>2016-07-19 16:40:22 -0700
commitb8247f095eddfbfdba0fcecd1e3525a6cdb4b585 (patch)
tree040f73dd021e9395a688bc9db01fc1dfae70e230 /net/ipv4/ip_tunnel_core.c
parentnet/ipv4: Introduce IPSKB_FRAG_SEGS bit to inet_skb_parm.flags (diff)
net: ip_finish_output_gso: If skb_gso_network_seglen exceeds MTU, allow segmentation for local udp tunneled skbs
Given: - tap0 and vxlan0 are bridged - vxlan0 stacked on eth0, eth0 having small mtu (e.g. 1400) Assume GSO skbs arriving from tap0 having a gso_size as determined by user-provided virtio_net_hdr (e.g. 1460 corresponding to VM mtu of 1500). After encapsulation these skbs have skb_gso_network_seglen that exceed eth0's ip_skb_dst_mtu. These skbs are accidentally passed to ip_finish_output2 AS IS. Alas, each final segment (segmented either by validate_xmit_skb or by hardware UFO) would be larger than eth0 mtu. As a result, those above-mtu segments get dropped on certain networks. This behavior is not aligned with the NON-GSO case: Assume a non-gso 1500-sized IP packet arrives from tap0. After encapsulation, the vxlan datagram is fragmented normally at the ip_finish_output-->ip_fragment code path. The expected behavior for the GSO case would be segmenting the "gso-oversized" skb first, then fragmenting each segment according to dst mtu, and finally passing the resulting fragments to ip_finish_output2. 'ip_finish_output_gso' already supports this "Slowpath" behavior, according to the IPSKB_FRAG_SEGS flag, which is only set during ipv4 forwarding (not set in the bridged case). In order to support the bridged case, we'll mark skbs arriving from an ingress interface that get udp-encaspulated as "allowed to be fragmented", causing their network_seglen to be validated by 'ip_finish_output_gso' (and fragment if needed). Note the TUNNEL_DONT_FRAGMENT tun_flag is still honoured (both in the gso and non-gso cases), which serves users wishing to forbid fragmentation at the udp tunnel endpoint. Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Cc: Florian Westphal <fw@strlen.de> Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com> Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/ip_tunnel_core.c')
1 files changed, 9 insertions, 0 deletions
diff --git a/net/ipv4/ip_tunnel_core.c b/net/ipv4/ip_tunnel_core.c
index afd6b5968caf..9d847c302551 100644
--- a/net/ipv4/ip_tunnel_core.c
+++ b/net/ipv4/ip_tunnel_core.c
@@ -63,6 +63,7 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
int pkt_len = skb->len - skb_inner_network_offset(skb);
struct net *net = dev_net(rt->dst.dev);
struct net_device *dev = skb->dev;
+ int skb_iif = skb->skb_iif;
struct iphdr *iph;
int err;
@@ -72,6 +73,14 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb,
skb_dst_set(skb, &rt->dst);
memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
+ if (skb_iif && proto == IPPROTO_UDP) {
+ /* Arrived from an ingress interface and got udp encapuslated.
+ * The encapsulated network segment length may exceed dst mtu.
+ * Allow IP Fragmentation of segments.
+ */
+ IPCB(skb)->flags |= IPSKB_FRAG_SEGS;
+ }
/* Push down and install the IP header. */
skb_push(skb, sizeof(struct iphdr));