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    Subject[PATCH 3.16.y-ckt 012/126] net: fix a race in dst_release()
    Date
    3.16.7-ckt21 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>

    commit d69bbf88c8d0b367cf3e3a052f6daadf630ee566 upstream.

    Only cpu seeing dst refcount going to 0 can safely
    dereference dst->flags.

    Otherwise an other cpu might already have freed the dst.

    Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
    Reported-by: Greg Thelen <gthelen@google.com>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [ luis: backported to 3.16: adjusted context ]
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    net/core/dst.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/core/dst.c b/net/core/dst.c
    index a028409ee438..a80e92346b9b 100644
    --- a/net/core/dst.c
    +++ b/net/core/dst.c
    @@ -285,7 +285,7 @@ void dst_release(struct dst_entry *dst)

    newrefcnt = atomic_dec_return(&dst->__refcnt);
    WARN_ON(newrefcnt < 0);
    - if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt)
    + if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
    call_rcu(&dst->rcu_head, dst_destroy_rcu);
    }
    }

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