4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> [ Upstream commit 82612de1c98e610d194e34178bde3cca7dedce41 ] After commit f6cc9c054e77, the following conf is broken (note that the default loopback mtu is 65536, ie IP_MAX_MTU + 1): $ ip tunnel add gre1 mode gre local 10.125.0.1 remote 10.125.0.2 dev lo add tunnel "gre0" failed: Invalid argument $ ip l a type dummy $ ip l s dummy1 up $ ip l s dummy1 mtu 65535 $ ip tunnel add gre1 mode gre local 10.125.0.1 remote 10.125.0.2 dev dummy1 add tunnel "gre0" failed: Invalid argument dev_set_mtu() doesn't allow to set a mtu which is too large. First, let's cap the mtu returned by ip_tunnel_bind_dev(). Second, remove the magic value 0xFFF8 and use IP_MAX_MTU instead. 0xFFF8 seems to be there for ages, I don't know why this value was used. With a recent kernel, it's also possible to set a mtu > IP_MAX_MTU: $ ip l s dummy1 mtu 66000 After that patch, it's also possible to bind an ip tunnel on that kind of interface. CC: Petr Machata <petrm@xxxxxxxxxxxx> CC: Ido Schimmel <idosch@xxxxxxxxxxxx> Link: https://git.kernel.org/pub/scm/linux/kernel/git/davem/netdev-vger-cvs.git/commit/?id=e5afd356a411a Fixes: f6cc9c054e77 ("ip_tunnel: Emit events for post-register MTU changes") Signed-off-by: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/ipv4/ip_tunnel.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -344,7 +344,7 @@ static int ip_tunnel_bind_dev(struct net if (tdev) { hlen = tdev->hard_header_len + tdev->needed_headroom; - mtu = tdev->mtu; + mtu = min(tdev->mtu, IP_MAX_MTU); } dev->needed_headroom = t_hlen + hlen; @@ -379,7 +379,7 @@ 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 = 0xFFF8 - dev->hard_header_len - t_hlen; + dev->max_mtu = IP_MAX_MTU - dev->hard_header_len - t_hlen; ip_tunnel_add(itn, nt); return nt; @@ -948,7 +948,7 @@ 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 = 0xFFF8 - dev->hard_header_len - t_hlen; + int max_mtu = IP_MAX_MTU - dev->hard_header_len - t_hlen; if (new_mtu < ETH_MIN_MTU) return -EINVAL; @@ -1119,7 +1119,7 @@ int ip_tunnel_newlink(struct net_device mtu = ip_tunnel_bind_dev(dev); if (tb[IFLA_MTU]) { - unsigned int max = 0xfff8 - dev->hard_header_len - nt->hlen; + unsigned int max = IP_MAX_MTU - dev->hard_header_len - nt->hlen; mtu = clamp(dev->mtu, (unsigned int)ETH_MIN_MTU, (unsigned int)(max - sizeof(struct iphdr)));
