netdev - [PATCH net] net: ip_tunnel: fix mtu calculation for ETHER tunnel devices

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Message-Id: <20210709034502.1227174-1-liuhangbin@gmail.com>
Date:   Fri,  9 Jul 2021 11:45:02 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     netdev@...r.kernel.org
Cc:     Vadim Fedorenko <vfedorenko@...ek.ru>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jianlin Shi <jishi@...hat.com>
Subject: [PATCH net] net: ip_tunnel: fix mtu calculation for ETHER tunnel devices

Commit 28e104d00281 ("net: ip_tunnel: fix mtu calculation") removed
dev->hard_header_len subtraction when calculate MTU for tunnel devices
as there is an overhead for device that has header_ops.

But there are ETHER tunnel devices, like gre_tap or erspan, which don't
have header_ops but set dev->hard_header_len during setup. This makes
pkts greater than (MTU - ETH_HLEN) could not be xmited. Fix it by
subtracting the ETHER tunnel devices' dev->hard_header_len for MTU
calculation.

Fixes: 28e104d00281 ("net: ip_tunnel: fix mtu calculation")
Reported-by: Jianlin Shi <jishi@...hat.com>
Signed-off-by: Hangbin Liu <liuhangbin@...il.com>
---
 net/ipv4/ip_tunnel.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index f6cc26de5ed3..0dca00745ac3 100644
--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -317,7 +317,7 @@ static int ip_tunnel_bind_dev(struct net_device *dev)
 	}
 
 	dev->needed_headroom = t_hlen + hlen;
-	mtu -= t_hlen;
+	mtu -= t_hlen + (dev->type == ARPHRD_ETHER ? dev->hard_header_len : 0);
 
 	if (mtu < IPV4_MIN_MTU)
 		mtu = IPV4_MIN_MTU;
@@ -348,6 +348,9 @@ static struct ip_tunnel *ip_tunnel_create(struct net *net,
 	t_hlen = nt->hlen + sizeof(struct iphdr);
 	dev->min_mtu = ETH_MIN_MTU;
 	dev->max_mtu = IP_MAX_MTU - t_hlen;
+	if (dev->type == ARPHRD_ETHER)
+		dev->max_mtu -= dev->hard_header_len;
+
 	ip_tunnel_add(itn, nt);
 	return nt;
 
@@ -489,11 +492,14 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb,
 
 	tunnel_hlen = md ? tunnel_hlen : tunnel->hlen;
 	pkt_size = skb->len - tunnel_hlen;
+	pkt_size -= dev->type == ARPHRD_ETHER ? dev->hard_header_len : 0;
 
-	if (df)
+	if (df) {
 		mtu = dst_mtu(&rt->dst) - (sizeof(struct iphdr) + tunnel_hlen);
-	else
+		mtu -= dev->type == ARPHRD_ETHER ? dev->hard_header_len : 0;
+	} else {
 		mtu = skb_valid_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
+	}
 
 	if (skb_valid_dst(skb))
 		skb_dst_update_pmtu_no_confirm(skb, mtu);
@@ -972,6 +978,9 @@ int __ip_tunnel_change_mtu(struct net_device *dev, int new_mtu, bool strict)
 	int t_hlen = tunnel->hlen + sizeof(struct iphdr);
 	int max_mtu = IP_MAX_MTU - t_hlen;
 
+	if (dev->type == ARPHRD_ETHER)
+		max_mtu -= dev->hard_header_len;
+
 	if (new_mtu < ETH_MIN_MTU)
 		return -EINVAL;
 
@@ -1149,6 +1158,9 @@ int ip_tunnel_newlink(struct net_device *dev, struct nlattr *tb[],
 	if (tb[IFLA_MTU]) {
 		unsigned int max = IP_MAX_MTU - (nt->hlen + sizeof(struct iphdr));
 
+		if (dev->type == ARPHRD_ETHER)
+			max -= dev->hard_header_len;
+
 		mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU, max);
 	}
 
-- 
2.31.1