net: ipv4: update fnhe_pmtu when first hop's MTU changes

Since commit 5aad1de5ea2c ("ipv4: use separate genid for next hop
exceptions"), exceptions get deprecated separately from cached
routes. In particular, administrative changes don't clear PMTU anymore.

As Stefano described in commit e9fa1495d738 ("ipv6: Reflect MTU changes
on PMTU of exceptions for MTU-less routes"), the PMTU discovered before
the local MTU change can become stale:
 - if the local MTU is now lower than the PMTU, that PMTU is now
   incorrect
 - if the local MTU was the lowest value in the path, and is increased,
   we might discover a higher PMTU

Similarly to what commit e9fa1495d738 did for IPv6, update PMTU in those
cases.

If the exception was locked, the discovered PMTU was smaller than the
minimal accepted PMTU. In that case, if the new local MTU is smaller
than the current PMTU, let PMTU discovery figure out if locking of the
exception is still needed.

To do this, we need to know the old link MTU in the NETDEV_CHANGEMTU
notifier. By the time the notifier is called, dev->mtu has been
changed. This patch adds the old MTU as additional information in the
notifier structure, and a new call_netdevice_notifiers_u32() function.

Fixes: 5aad1de5ea2c ("ipv4: use separate genid for next hop exceptions")
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Reviewed-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 26 insertions, 2 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 82114e1111e6..93243479085f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1752,6 +1752,28 @@ int call_netdevice_notifiers(unsigned long val, struct net_device *dev)
 }
 EXPORT_SYMBOL(call_netdevice_notifiers);
 
+/**
+ *      call_netdevice_notifiers_mtu - call all network notifier blocks
+ *      @val: value passed unmodified to notifier function
+ *      @dev: net_device pointer passed unmodified to notifier function
+ *      @arg: additional u32 argument passed to the notifier function
+ *
+ *      Call all network notifier blocks.  Parameters and return value
+ *      are as for raw_notifier_call_chain().
+ */
+static int call_netdevice_notifiers_mtu(unsigned long val,
+                                        struct net_device *dev, u32 arg)
+{
+        struct netdev_notifier_info_ext info = {
+                .info.dev = dev,
+                .ext.mtu = arg,
+        };
+
+        BUILD_BUG_ON(offsetof(struct netdev_notifier_info_ext, info) != 0);
+
+        return call_netdevice_notifiers_info(val, &info.info);
+}
+
 #ifdef CONFIG_NET_INGRESS
 static DEFINE_STATIC_KEY_FALSE(ingress_needed_key);
 
@@ -7574,14 +7596,16 @@ int dev_set_mtu_ext(struct net_device *dev, int new_mtu,
         err = __dev_set_mtu(dev, new_mtu);
 
         if (!err) {
-                err = call_netdevice_notifiers(NETDEV_CHANGEMTU, dev);
+                err = call_netdevice_notifiers_mtu(NETDEV_CHANGEMTU, dev,
+                                                   orig_mtu);
                 err = notifier_to_errno(err);
                 if (err) {
                         /* setting mtu back and notifying everyone again,
                          * so that they have a chance to revert changes.
                          */
                         __dev_set_mtu(dev, orig_mtu);
-                        call_netdevice_notifiers(NETDEV_CHANGEMTU, dev);
+                        call_netdevice_notifiers_mtu(NETDEV_CHANGEMTU, dev,
+                                                     new_mtu);
                 }
         }
         return err;