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    Subject[PATCH 3.10 225/319] ipv6: correctly add local routes when lo goes up
    Date
    From: Nicolas Dichtel <nicolas.dichtel@6wind.com>

    commit a220445f9f4382c36a53d8ef3e08165fa27f7e2c upstream.

    The goal of the patch is to fix this scenario:
    ip link add dummy1 type dummy
    ip link set dummy1 up
    ip link set lo down ; ip link set lo up

    After that sequence, the local route to the link layer address of dummy1 is
    not there anymore.

    When the loopback is set down, all local routes are deleted by
    addrconf_ifdown()/rt6_ifdown(). At this time, the rt6_info entry still
    exists, because the corresponding idev has a reference on it. After the rcu
    grace period, dst_rcu_free() is called, and thus ___dst_free(), which will
    set obsolete to DST_OBSOLETE_DEAD.

    In this case, init_loopback() is called before dst_rcu_free(), thus
    obsolete is still sets to something <= 0. So, the function doesn't add the
    route again. To avoid that race, let's check the rt6 refcnt instead.

    Fixes: 25fb6ca4ed9c ("net IPv6 : Fix broken IPv6 routing table after loopback down-up")
    Fixes: a881ae1f625c ("ipv6: don't call addrconf_dst_alloc again when enable lo")
    Fixes: 33d99113b110 ("ipv6: reallocate addrconf router for ipv6 address when lo device up")
    Reported-by: Francesco Santoro <francesco.santoro@6wind.com>
    Reported-by: Samuel Gauthier <samuel.gauthier@6wind.com>
    CC: Balakumaran Kannan <Balakumaran.Kannan@ap.sony.com>
    CC: Maruthi Thotad <Maruthi.Thotad@ap.sony.com>
    CC: Sabrina Dubroca <sd@queasysnail.net>
    CC: Hannes Frederic Sowa <hannes@stressinduktion.org>
    CC: Weilong Chen <chenweilong@huawei.com>
    CC: Gao feng <gaofeng@cn.fujitsu.com>
    Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Willy Tarreau <w@1wt.eu>
    ---
    net/ipv6/addrconf.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
    index 3bfd8a5..a3e2c34 100644
    --- a/net/ipv6/addrconf.c
    +++ b/net/ipv6/addrconf.c
    @@ -2709,7 +2709,7 @@ static void init_loopback(struct net_device *dev)
    * lo device down, release this obsolete dst and
    * reallocate a new router for ifa.
    */
    - if (sp_ifa->rt->dst.obsolete > 0) {
    + if (!atomic_read(&sp_ifa->rt->rt6i_ref)) {
    ip6_rt_put(sp_ifa->rt);
    sp_ifa->rt = NULL;
    } else {
    --
    2.8.0.rc2.1.gbe9624a
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