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    Subject[PATCH 3.2 091/106] ipv6: avoid unregistering inet6_dev for loopback
    3.2.93-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: WANG Cong <xiyou.wangcong@gmail.com>

    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>
    ---
    --- a/net/ipv6/addrconf.c
    +++ b/net/ipv6/addrconf.c
    @@ -2633,6 +2633,7 @@ static int addrconf_notify(struct notifi
    {
    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 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;

    @@ -2754,6 +2755,8 @@ static int addrconf_notify(struct notifi
    * 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:
    \
     
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