linux-kernel - [PATCH AUTOSEL for 4.9 024/156] netfilter: bridge: honor frag_max

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Message-ID: <20171207154845.4814-24-alexander.levin@verizon.com>
Date:   Thu, 7 Dec 2017 15:49:00 +0000
From:   alexander.levin@...izon.com
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc:     Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        alexander.levin@...izon.com
Subject: [PATCH AUTOSEL for 4.9 024/156] netfilter: bridge: honor
 frag_max_size when refragmenting

From: Florian Westphal <fw@...len.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@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
---
 net/bridge/br_netfilter_hooks.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/net/bridge/br_netfilter_hooks.c b/net/bridge/br_netfilter_hooks.c
index aa1df1a10dd7..82ce5713f744 100644
--- a/net/bridge/br_netfilter_hooks.c
+++ b/net/bridge/br_netfilter_hooks.c
@@ -706,18 +706,20 @@ 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.
 	 */
-- 
2.11.0