[PATCH 5.4 62/65] net: ip_tunnel: fix mtu calculation

Greg Kroah-Hartman
2021-02-08T17:46:30Z

From: Vadim Fedorenko <vfedorenko@novek.ru>

commit 28e104d00281ade30250b24e098bf50887671ea4 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_tunnel.c | 16 +++++++---------
1 file changed, 7 insertions(+), 9 deletions(-)

--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -317,7 +317,7 @@ static int ip_tunnel_bind_dev(struct net
}

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_creat
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;

@@ -494,11 +494,10 @@ static int tnl_update_pmtu(struct net_de
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;

@@ -964,7 +963,7 @@ int __ip_tunnel_change_mtu(struct net_de
{
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;
@@ -1141,10 +1140,9 @@ int ip_tunnel_newlink(struct net_device

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);