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    Subject[PATCH 4.4 65/84] ipv6: flowlabel: fl6_sock_lookup() must use atomic_inc_not_zero
    Date
    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 65a3c497c0e965a552008db8bc2653f62bc925a1 ]

    Before taking a refcount, make sure the object is not already
    scheduled for deletion.

    Same fix is needed in ipv6_flowlabel_opt()

    Fixes: 18367681a10b ("ipv6 flowlabel: Convert np->ipv6_fl_list to RCU.")
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Cc: Willem de Bruijn <willemb@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/ip6_flowlabel.c | 7 ++++---
    1 file changed, 4 insertions(+), 3 deletions(-)

    --- a/net/ipv6/ip6_flowlabel.c
    +++ b/net/ipv6/ip6_flowlabel.c
    @@ -254,9 +254,9 @@ struct ip6_flowlabel *fl6_sock_lookup(st
    rcu_read_lock_bh();
    for_each_sk_fl_rcu(np, sfl) {
    struct ip6_flowlabel *fl = sfl->fl;
    - if (fl->label == label) {
    +
    + if (fl->label == label && atomic_inc_not_zero(&fl->users)) {
    fl->lastuse = jiffies;
    - atomic_inc(&fl->users);
    rcu_read_unlock_bh();
    return fl;
    }
    @@ -622,7 +622,8 @@ int ipv6_flowlabel_opt(struct sock *sk,
    goto done;
    }
    fl1 = sfl->fl;
    - atomic_inc(&fl1->users);
    + if (!atomic_inc_not_zero(&fl1->users))
    + fl1 = NULL;
    break;
    }
    }

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