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    Subject[PATCH 3.16 032/136] l2tp: ensure sessions are freed after their PPPOL2TP socket
    3.16.54-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Guillaume Nault <g.nault@alphalink.fr>

    commit cdd10c9627496ad25c87ce6394e29752253c69d3 upstream.

    If l2tp_tunnel_delete() or l2tp_tunnel_closeall() deletes a session
    right after pppol2tp_release() orphaned its socket, then the 'sock'
    variable of the pppol2tp_session_close() callback is NULL. Yet the
    session is still used by pppol2tp_release().

    Therefore we need to take an extra reference in any case, to prevent
    l2tp_tunnel_delete() or l2tp_tunnel_closeall() from freeing the session.

    Since the pppol2tp_session_close() callback is only set if the session
    is associated to a PPPOL2TP socket and that both l2tp_tunnel_delete()
    and l2tp_tunnel_closeall() hold the PPPOL2TP socket before calling
    pppol2tp_session_close(), we're sure that pppol2tp_session_close() and
    pppol2tp_session_destruct() are paired and called in the right order.
    So the reference taken by the former will be released by the later.

    Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/l2tp/l2tp_ppp.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    --- a/net/l2tp/l2tp_ppp.c
    +++ b/net/l2tp/l2tp_ppp.c
    @@ -456,11 +456,11 @@ static void pppol2tp_session_close(struc

    BUG_ON(session->magic != L2TP_SESSION_MAGIC);

    - if (sock) {
    + if (sock)
    inet_shutdown(sock, 2);
    - /* Don't let the session go away before our socket does */
    - l2tp_session_inc_refcount(session);
    - }
    +
    + /* Don't let the session go away before our socket does */
    + l2tp_session_inc_refcount(session);
    }

    /* Really kill the session socket. (Called from sock_put() if
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