| Message ID | 20170309222230.2190-1-fw@strlen.de |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
On Thu, Mar 09, 2017 at 11:22:30PM +0100, Florian Westphal wrote: > 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. Applied, thanks Florian. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c index 95087e6e8258..3c5185021c1c 100644 --- 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. */
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> --- changes since v1: only use nonzero frag_max_size, else non-fragmented packets won't be forwarded anymore. tested in kvm with both ipv4 and ipv6 and following setup: client (mtu 1500) --- bridge(mtu 9k) --- client (mtu 1500) bridge (incl. all ports) have 9k mtu. I tested ping & ping6 with sizes of 64, 8000, 32000. Without patch, 8000-sized packets are dropped on the bridge.