3.16.48-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: WANG Cong <xiyou.wangcong@xxxxxxxxx> 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@xxxxxxxxxx> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Cc: Daniel Lezcano <dlezcano@xxxxxxxxxx> Cc: David Ahern <dsahern@xxxxxxxxx> Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx> Acked-by: David Ahern <dsahern@xxxxxxxxx> Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> [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 <ben@xxxxxxxxxxxxxxx> --- --- 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); } break; @@ -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; case NETDEV_DOWN: case NETDEV_UNREGISTER: