net: ip_tunnel: fix mtu calculation

dev->hard_header_len for tunnel interface is set only when header_ops
are set too and already contains full overhead of any tunnel encapsulation.
That's why there is not need to use this overhead twice in mtu calc.

Fixes: fdafed459998 ("ip_gre: set dev->hard_header_len and dev->needed_headroom properly")
Reported-by: Slava Bacherikov <mail@slava.cc>
Signed-off-by: Vadim Fedorenko <vfedorenko@novek.ru>
Link: https://lore.kernel.org/r/1611959267-20536-1-git-send-email-vfedorenko@novek.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
index 64594aa755f0549081185575c5108e753f50749c..76a420c76f16e701d36e0ffe235fc19e0ccd8235 100644 (file)
--- 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 -= (dev->hard_header_len + t_hlen);
+       mtu -= t_hlen;
 
        if (mtu < IPV4_MIN_MTU)
                mtu = IPV4_MIN_MTU;
@@ -347,7 +347,7 @@ static struct ip_tunnel *ip_tunnel_create(struct net *net,
        nt = netdev_priv(dev);
        t_hlen = nt->hlen + sizeof(struct iphdr);
        dev->min_mtu = ETH_MIN_MTU;
-       dev->max_mtu = IP_MAX_MTU - dev->hard_header_len - t_hlen;
+       dev->max_mtu = IP_MAX_MTU - t_hlen;
        ip_tunnel_add(itn, nt);
        return nt;
 
@@ -488,11 +488,10 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb,
        int mtu;
 
        tunnel_hlen = md ? tunnel_hlen : tunnel->hlen;
-       pkt_size = skb->len - tunnel_hlen - dev->hard_header_len;
+       pkt_size = skb->len - tunnel_hlen;
 
        if (df)
-               mtu = dst_mtu(&rt->dst) - dev->hard_header_len
-                                       - sizeof(struct iphdr) - tunnel_hlen;
+               mtu = dst_mtu(&rt->dst) - (sizeof(struct iphdr) + tunnel_hlen);
        else
                mtu = skb_valid_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
 
@@ -972,7 +971,7 @@ int __ip_tunnel_change_mtu(struct net_device *dev, int new_mtu, bool strict)
 {
        struct ip_tunnel *tunnel = netdev_priv(dev);
        int t_hlen = tunnel->hlen + sizeof(struct iphdr);
-       int max_mtu = IP_MAX_MTU - dev->hard_header_len - t_hlen;
+       int max_mtu = IP_MAX_MTU - t_hlen;
 
        if (new_mtu < ETH_MIN_MTU)
                return -EINVAL;
@@ -1149,10 +1148,9 @@ int ip_tunnel_newlink(struct net_device *dev, struct nlattr *tb[],
 
        mtu = ip_tunnel_bind_dev(dev);
        if (tb[IFLA_MTU]) {
-               unsigned int max = IP_MAX_MTU - dev->hard_header_len - nt->hlen;
+               unsigned int max = IP_MAX_MTU - (nt->hlen + sizeof(struct iphdr));
 
-               mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU,
-                           (unsigned int)(max - sizeof(struct iphdr)));
+               mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU, max);
        }
 
        err = dev_set_mtu(dev, mtu);