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Subject[PATCH 3.16 212/233] ipv6: avoid unregistering inet6_dev for loopback
3.16.48-rc1 review patch.  If anyone has any objections, please let me know.


From: WANG Cong <>

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

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 <>
Cc: Andrey Konovalov <>
Cc: Daniel Lezcano <>
Cc: David Ahern <>
Signed-off-by: Cong Wang <>
Acked-by: David Ahern <>
Tested-by: Andrey Konovalov <>
Signed-off-by: David S. Miller <>
[bwh: Backported to 3.16: 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 <>
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2823,6 +2823,7 @@ static int addrconf_notify(struct notifi
struct net_device *dev = netdev_notifier_info_to_dev(ptr);
struct inet6_dev *idev = __in6_dev_get(dev);
+ struct net *net = dev_net(dev);
int run_pending = 0;
int err;

@@ -2916,7 +2917,7 @@ static int addrconf_notify(struct notifi
* 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);

@@ -2937,6 +2938,8 @@ static int addrconf_notify(struct notifi
* if MTU under IPV6_MIN_MTU.
* Stop IPv6 on this interface.
+ addrconf_ifdown(dev, dev != net->loopback_dev);
+ break;

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