3.16.60-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Nicolas Dichtel <nicolas.dichtel@xxxxxxxxx> commit 82612de1c98e610d194e34178bde3cca7dedce41 upstream. 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> [bwh: Backported to 3.16: - Drop change in ip_tunnel_create() - Adjust context] Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -387,7 +387,7 @@ 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->iflink = tunnel->parms.link; @@ -851,7 +851,7 @@ int ip_tunnel_change_mtu(struct net_devi int t_hlen = tunnel->hlen + sizeof(struct iphdr); if (new_mtu < 68 || - new_mtu > 0xFFF8 - dev->hard_header_len - t_hlen) + new_mtu > IP_MAX_MTU - dev->hard_header_len - t_hlen) return -EINVAL; dev->mtu = new_mtu; return 0; @@ -979,7 +979,7 @@ 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)));
