On Wed, Jun 21, 2017 at 11:34 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
> 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.
Thanks! This fixes the bug for me.
Tested-by: Andrey Konovalov <andreyk...@google.com>
>
> Fixes: 176c39af29bc ("netns: fix addrconf_ifdown kernel panic")
> Reported-by: Andrey Konovalov <andreyk...@google.com>
> Cc: Andrey Konovalov <andreyk...@google.com>
> Cc: Daniel Lezcano <dlezc...@fr.ibm.com>
> Cc: David Ahern <dsah...@gmail.com>
> Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
> ---
> net/ipv6/addrconf.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 686c923..1d2dbac 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3369,6 +3369,7 @@ static int addrconf_notify(struct notifier_block *this,
> unsigned long event,
> struct net_device *dev = netdev_notifier_info_to_dev(ptr);
> struct netdev_notifier_changeupper_info *info;
> struct inet6_dev *idev = __in6_dev_get(dev);
> + struct net *net = dev_net(dev);
> int run_pending = 0;
> int err;
>
> @@ -3384,7 +3385,7 @@ static int addrconf_notify(struct notifier_block *this,
> unsigned long event,
> case NETDEV_CHANGEMTU:
> /* if MTU under 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;
> }
>
> @@ -3500,7 +3501,7 @@ 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;
>
> --
> 2.5.5
>
