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    Subject[PATCH 4.1 075/127] ipv6: tcp: add rcu locking in tcp_v6_send_synack()
    Date
    4.1-stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Dumazet <edumazet@google.com>

    [ Upstream commit 3e4006f0b86a5ae5eb0e8215f9a9e1db24506977 ]

    When first SYNACK is sent, we already hold rcu_read_lock(), but this
    is not true if a SYNACK is retransmitted, as a timer (soft) interrupt
    does not hold rcu_read_lock()

    Fixes: 45f6fad84cc30 ("ipv6: add complete rcu protection around np->opt")
    Reported-by: Dave Jones <davej@codemonkey.org.uk>
    Signed-off-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/ipv6/tcp_ipv6.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/net/ipv6/tcp_ipv6.c
    +++ b/net/ipv6/tcp_ipv6.c
    @@ -465,8 +465,10 @@ static int tcp_v6_send_synack(struct soc
    fl6->flowlabel = ip6_flowlabel(ipv6_hdr(ireq->pktopts));

    skb_set_queue_mapping(skb, queue_mapping);
    + rcu_read_lock();
    err = ip6_xmit(sk, skb, fl6, rcu_dereference(np->opt),
    np->tclass);
    + rcu_read_unlock();
    err = net_xmit_eval(err);
    }


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