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    Subject[128/143] l2tp: Fix UDP socket reference count bugs in the pppol2tp driver
    2.6.32-longterm review patch.  If anyone has any objections, please let us know.

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

    From: James Chapman <jchapman@katalix.com>

    commit c3259c8a7060d480e8eb2166da0a99d6879146b4 upstream.

    This patch fixes UDP socket refcnt bugs in the pppol2tp driver.

    A bug can cause a kernel stack trace when a tunnel socket is closed.

    A way to reproduce the issue is to prepare the UDP socket for L2TP (by
    opening a tunnel pppol2tp socket) and then close it before any L2TP
    sessions are added to it. The sequence is

    Create UDP socket
    Create tunnel pppol2tp socket to prepare UDP socket for L2TP
    pppol2tp_connect: session_id=0, peer_session_id=0
    L2TP SCCRP control frame received (tunnel_id==0)
    pppol2tp_recv_core: sock_hold()
    pppol2tp_recv_core: sock_put
    L2TP ZLB control frame received (tunnel_id=nnn)
    pppol2tp_recv_core: sock_hold()
    pppol2tp_recv_core: sock_put
    Close tunnel management socket
    pppol2tp_release: session_id=0, peer_session_id=0
    Close UDP socket
    udp_lib_close: BUG

    The addition of sock_hold() in pppol2tp_connect() solves the problem.

    For data frames, two sock_put() calls were added to plug a refcnt leak
    per received data frame. The ref that is grabbed at the top of
    pppol2tp_recv_core() must always be released, but this wasn't done for
    accepted data frames or data frames discarded because of bad UDP
    checksums. This leak meant that any UDP socket that had passed L2TP
    data traffic (i.e. L2TP data frames, not just L2TP control frames)
    using pppol2tp would not be released by the kernel.

    WARNING: at include/net/sock.h:435 udp_lib_unhash+0x117/0x120()
    Pid: 1086, comm: openl2tpd Not tainted 2.6.33-rc1 #8
    Call Trace:
    [<c119e9b7>] ? udp_lib_unhash+0x117/0x120
    [<c101b871>] ? warn_slowpath_common+0x71/0xd0
    [<c119e9b7>] ? udp_lib_unhash+0x117/0x120
    [<c101b8e3>] ? warn_slowpath_null+0x13/0x20
    [<c119e9b7>] ? udp_lib_unhash+0x117/0x120
    [<c11598a7>] ? sk_common_release+0x17/0x90
    [<c11a5e33>] ? inet_release+0x33/0x60
    [<c11577b0>] ? sock_release+0x10/0x60
    [<c115780f>] ? sock_close+0xf/0x30
    [<c106e542>] ? __fput+0x52/0x150
    [<c106b68e>] ? filp_close+0x3e/0x70
    [<c101d2e2>] ? put_files_struct+0x62/0xb0
    [<c101eaf7>] ? do_exit+0x5e7/0x650
    [<c1081623>] ? mntput_no_expire+0x13/0x70
    [<c106b68e>] ? filp_close+0x3e/0x70
    [<c101eb8a>] ? do_group_exit+0x2a/0x70
    [<c101ebe1>] ? sys_exit_group+0x11/0x20
    [<c10029b0>] ? sysenter_do_call+0x12/0x26

    Signed-off-by: James Chapman <jchapman@katalix.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
    ---
    drivers/net/pppol2tp.c | 3 +++
    1 file changed, 3 insertions(+)

    --- a/drivers/net/pppol2tp.c
    +++ b/drivers/net/pppol2tp.c
    @@ -756,6 +756,7 @@ static int pppol2tp_recv_core(struct soc

    /* Try to dequeue as many skbs from reorder_q as we can. */
    pppol2tp_recv_dequeue(session);
    + sock_put(sock);

    return 0;

    @@ -772,6 +773,7 @@ discard_bad_csum:
    UDP_INC_STATS_USER(&init_net, UDP_MIB_INERRORS, 0);
    tunnel->stats.rx_errors++;
    kfree_skb(skb);
    + sock_put(sock);

    return 0;

    @@ -1658,6 +1660,7 @@ static int pppol2tp_connect(struct socke
    if (tunnel_sock == NULL)
    goto end;

    + sock_hold(tunnel_sock);
    tunnel = tunnel_sock->sk_user_data;
    } else {
    tunnel = pppol2tp_tunnel_find(sock_net(sk), sp->pppol2tp.s_tunnel);



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