[PATCH 4.19 052/120] net: ip_tunnel: fix mtu calculation for ETHER tunnel devices

Greg Kroah-Hartman
2021-07-26T15:59:43Z

From: Hangbin Liu <liuhangbin@gmail.com>

commit 9992a078b1771da354ac1f9737e1e639b687caa2 upstream.

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@redhat.com>
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/ip_tunnel.c | 22 ++++++++++++++++++----
1 file changed, 18 insertions(+), 4 deletions(-)

--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -330,7 +330,7 @@ static int ip_tunnel_bind_dev(struct net
}

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;
@@ -361,6 +361,9 @@ static struct ip_tunnel *ip_tunnel_creat
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;

@@ -502,13 +505,18 @@ static int tnl_update_pmtu(struct net_de
const struct iphdr *inner_iph)
{
struct ip_tunnel *tunnel = netdev_priv(dev);
- int pkt_size = skb->len - tunnel->hlen;
+ int pkt_size;
int mtu;

- if (df)
+ pkt_size = skb->len - tunnel->hlen;
+ pkt_size -= dev->type == ARPHRD_ETHER ? dev->hard_header_len : 0;
+
+ 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_dst(skb) ? dst_mtu(skb_dst(skb)) : dev->mtu;
+ }

skb_dst_update_pmtu_no_confirm(skb, mtu);

@@ -936,6 +944,9 @@ int __ip_tunnel_change_mtu(struct net_de
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;

@@ -1113,6 +1124,9 @@ int ip_tunnel_newlink(struct net_device
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);
}