[PATCH 4.16 45/48] ip_tunnel: restore binding to ifaces with a large mtu
From: Greg Kroah-Hartman
Date: Sat Jun 09 2018 - 11:34:24 EST
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)));