[PATCH 4.4 031/115] netfilter: bridge: honor frag_max_size when refragmenting

Greg Kroah-Hartman
2017-12-18T15:53:35Z

From: Florian Westphal <fw@strlen.de>

[ Upstream commit 4ca60d08cbe65f501baad64af50fceba79c19fbb ]

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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/bridge/br_netfilter_hooks.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -701,18 +701,20 @@ static unsigned int nf_bridge_mtu_reduct

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 (skb_is_gso(skb) || skb->len + mtu_reserved <= 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 <= 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.
*/