netfilter: bridge-netfilter: fix refragmenting IP traffic encapsulated in PPPoE traffic

The MTU for IP traffic encapsulated inside PPPoE traffic is smaller
than the MTU of the Ethernet device (1500). Connection tracking
gathers all IP packets and sometimes will refragment them in
ip_fragment(). We then need to subtract the length of the
encapsulating header from the mtu used in ip_fragment(). The check in
br_nf_dev_queue_xmit() which determines if ip_fragment() has to be
called is also updated for the PPPoE-encapsulated packets.
nf_bridge_copy_header() is also updated to make sure the PPPoE data
length field has the correct value.

Signed-off-by: Bart De Schuymer <bdschuym@pandora.be>
Signed-off-by: Patrick McHardy <kaber@trash.net>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index b0b2e3059f11..d979710684b2 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -469,6 +469,10 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
 
         hlen = iph->ihl * 4;
         mtu = dst_mtu(&rt->u.dst) - hlen;       /* Size of data space */
+#ifdef CONFIG_BRIDGE_NETFILTER
+        if (skb->nf_bridge)
+                mtu -= nf_bridge_mtu_reduction(skb);
+#endif
         IPCB(skb)->flags |= IPSKB_FRAG_COMPLETE;
 
         /* When frag_list is given, use it. First, check its validity: