| Message ID | 20180530082843.6076-2-nicolas.dichtel@6wind.com |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
| Series | ip[6] tunnels: fix mtu calculations | expand |
On Wed, May 30, 2018 at 10:28:42AM +0200, Nicolas Dichtel wrote: > 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@mellanox.com> > CC: Ido Schimmel <idosch@mellanox.com> > 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@6wind.com> Reviewed-by: Ido Schimmel <idosch@mellanox.com> There is another instance of this magic number in the file, but it's written in lower case so you might have missed it - see ip_tunnel_newlink(). Can you please take care of it in v2? Thanks for the fix, Nicolas!
Le 30/05/2018 à 22:29, Ido Schimmel a écrit : [snip] > There is another instance of this magic number in the file, but it's > written in lower case so you might have missed it - see > ip_tunnel_newlink(). Can you please take care of it in v2? Good catch, thank you. Will send a v2.
diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 6b0e362cc99b..3b39c72a1029 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -328,7 +328,7 @@ static int ip_tunnel_bind_dev(struct net_device *dev) 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; @@ -362,7 +362,7 @@ 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 = 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; @@ -930,7 +930,7 @@ 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 = 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;
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@mellanox.com> CC: Ido Schimmel <idosch@mellanox.com> 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@6wind.com> --- net/ipv4/ip_tunnel.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)