netfilter: bridge: honor frag_max_size when refragmenting

consider a bridge with mtu 9000, but end host sending smaller
packets to another host with mtu < 9000.

In this case, after reassembly, bridge+defrag would refragment,
and then attempt to send the reassembled packet as long as it
was below 9k.

Instead we have to cap by the largest fragment size seen.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index 95087e6e8258366af95579bb308d1a6e18266f0e..3c5185021c1c0d3d8d5ba42a898bc328c4696d47 100644 (file)
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -721,18 +721,20 @@ static unsigned int nf_bridge_mtu_reduction(const struct sk_buff *skb)
 
 static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
-       struct nf_bridge_info *nf_bridge;
-       unsigned int mtu_reserved;
+       struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
+       unsigned int mtu, mtu_reserved;
 
        mtu_reserved = nf_bridge_mtu_reduction(skb);
+       mtu = skb->dev->mtu;
+
+       if (nf_bridge->frag_max_size && nf_bridge->frag_max_size < mtu)
+               mtu = nf_bridge->frag_max_size;
 
-       if (skb_is_gso(skb) || skb->len + mtu_reserved <= skb->dev->mtu) {
+       if (skb_is_gso(skb) || skb->len + mtu_reserved <= mtu) {
                nf_bridge_info_free(skb);
                return br_dev_queue_push_xmit(net, sk, skb);
        }
 
-       nf_bridge = nf_bridge_info_get(skb);
-
        /* This is wrong! We should preserve the original fragment
         * boundaries by preserving frag_list rather than refragmenting.
         */