ipv: Re-enable IP when MTU > 68

Re-enable IP when the MTU gets back to a valid size. 

This patch just checks if the in_dev is NULL on a NETDEV_CHANGEMTU event
and if MTU is valid (bigger than 68), then re-enable in_dev. 

Also a function that checks valid MTU size was created.

Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 12 insertions, 3 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index 91d3d96805d0..b12dae2b0b2d 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -1029,6 +1029,11 @@ skip:
         }
 }
 
+static inline bool inetdev_valid_mtu(unsigned mtu)
+{
+        return mtu >= 68;
+}
+
 /* Called only under RTNL semaphore */
 
 static int inetdev_event(struct notifier_block *this, unsigned long event,
@@ -1048,6 +1053,10 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
                                 IN_DEV_CONF_SET(in_dev, NOXFRM, 1);
                                 IN_DEV_CONF_SET(in_dev, NOPOLICY, 1);
                         }
+                } else if (event == NETDEV_CHANGEMTU) {
+                        /* Re-enabling IP */
+                        if (inetdev_valid_mtu(dev->mtu))
+                                in_dev = inetdev_init(dev);
                 }
                 goto out;
         }
@@ -1058,7 +1067,7 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
                 dev->ip_ptr = NULL;
                 break;
         case NETDEV_UP:
-                if (dev->mtu < 68)
+                if (!inetdev_valid_mtu(dev->mtu))
                         break;
                 if (dev->flags & IFF_LOOPBACK) {
                         struct in_ifaddr *ifa;
@@ -1080,9 +1089,9 @@ static int inetdev_event(struct notifier_block *this, unsigned long event,
                 ip_mc_down(in_dev);
                 break;
         case NETDEV_CHANGEMTU:
-                if (dev->mtu >= 68)
+                if (inetdev_valid_mtu(dev->mtu))
                         break;
-                /* MTU falled under 68, disable IP */
+                /* disable IP when MTU is not enough */
         case NETDEV_UNREGISTER:
                 inetdev_destroy(in_dev);
                 break;