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netfilter: bridge: honor frag_max_size when refragmenting

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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>
This commit is contained in:
Florian Westphal 2017-03-09 23:22:30 +01:00 committed by Pablo Neira Ayuso
parent 10596608c4
commit 4ca60d08cb
1 changed files with 7 additions and 5 deletions
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12
net/bridge/br_netfilter_hooks.c
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@ -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) static int br_nf_dev_queue_xmit(struct net *net, struct sock *sk, struct sk_buff *skb)
{ {
struct nf_bridge_info *nf_bridge; struct nf_bridge_info *nf_bridge = nf_bridge_info_get(skb);
unsigned int mtu_reserved; unsigned int mtu, mtu_reserved;
mtu_reserved = nf_bridge_mtu_reduction(skb); 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); nf_bridge_info_free(skb);
return br_dev_queue_push_xmit(net, sk, 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 /* This is wrong! We should preserve the original fragment
* boundaries by preserving frag_list rather than refragmenting. * boundaries by preserving frag_list rather than refragmenting.
*/ */