ipv6: avoid unregistering inet6_dev for loopback

commit 60abc0be96e00ca71bac083215ac91ad2e575096 upstream.

The per netns loopback_dev->ip6_ptr is unregistered and set to
NULL when its mtu is set to smaller than IPV6_MIN_MTU, this
leads to that we could set rt->rt6i_idev NULL after a
rt6_uncached_list_flush_dev() and then crash after another
call.

In this case we should just bring its inet6_dev down, rather
than unregistering it, at least prior to commit 176c39af29bc
("netns: fix addrconf_ifdown kernel panic") we always
override the case for loopback.

Thanks a lot to Andrey for finding a reliable reproducer.

Fixes: 176c39af29bc ("netns: fix addrconf_ifdown kernel panic")
Reported-by: Andrey Konovalov <andreyknvl@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Daniel Lezcano <dlezcano@fr.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Acked-by: David Ahern <dsahern@gmail.com>
Tested-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: the NETDEV_CHANGEMTU case used to fall-through to the
 NETDEV_DOWN case here, so replace that with a separate call to addrconf_ifdown()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 9a851d1..cb1de47 100644 (file)
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2633,6 +2633,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
 {
        struct net_device *dev = (struct net_device *) data;
        struct inet6_dev *idev = __in6_dev_get(dev);
+       struct net *net = dev_net(dev);
        int run_pending = 0;
        int err;
 
@@ -2733,7 +2734,7 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
                         * IPV6_MIN_MTU stop IPv6 on this interface.
                         */
                        if (dev->mtu < IPV6_MIN_MTU)
-                               addrconf_ifdown(dev, 1);
+                               addrconf_ifdown(dev, dev != net->loopback_dev);
                }
                break;
 
@@ -2754,6 +2755,8 @@ static int addrconf_notify(struct notifier_block *this, unsigned long event,
                 * MTU falled under IPV6_MIN_MTU.
                 * Stop IPv6 on this interface.
                 */
+               addrconf_ifdown(dev, dev != net->loopback_dev);
+               break;
 
        case NETDEV_DOWN:
        case NETDEV_UNREGISTER: