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    Subject[PATCH 4.4 028/342] bonding: Fix ARP monitor validation
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Jay Vosburgh <jay.vosburgh@canonical.com>

    [ Upstream commit 21a75f0915dde8674708b39abfcda113911c49b1 ]

    The current logic in bond_arp_rcv will accept an incoming ARP for
    validation if (a) the receiving slave is either "active" (which includes
    the currently active slave, or the current ARP slave) or, (b) there is a
    currently active slave, and it has received an ARP since it became active.
    For case (b), the receiving slave isn't the currently active slave, and is
    receiving the original broadcast ARP request, not an ARP reply from the
    target.

    This logic can fail if there is no currently active slave. In
    this situation, the ARP probe logic cycles through all slaves, assigning
    each in turn as the "current_arp_slave" for one arp_interval, then setting
    that one as "active," and sending an ARP probe from that slave. The
    current logic expects the ARP reply to arrive on the sending
    current_arp_slave, however, due to switch FDB updating delays, the reply
    may be directed to another slave.

    This can arise if the bonding slaves and switch are working, but
    the ARP target is not responding. When the ARP target recovers, a
    condition may result wherein the ARP target host replies faster than the
    switch can update its forwarding table, causing each ARP reply to be sent
    to the previous current_arp_slave. This will never pass the logic in
    bond_arp_rcv, as neither of the above conditions (a) or (b) are met.

    Some experimentation on a LAN shows ARP reply round trips in the
    200 usec range, but my available switches never update their FDB in less
    than 4000 usec.

    This patch changes the logic in bond_arp_rcv to additionally
    accept an ARP reply for validation on any slave if there is a current ARP
    slave and it sent an ARP probe during the previous arp_interval.

    Fixes: aeea64ac717a ("bonding: don't trust arp requests unless active slave really works")
    Cc: Veaceslav Falico <vfalico@gmail.com>
    Cc: Andy Gospodarek <gospo@cumulusnetworks.com>
    Signed-off-by: Jay Vosburgh <jay.vosburgh@canonical.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/bonding/bond_main.c | 39 ++++++++++++++++++++++++++++-----------
    1 file changed, 28 insertions(+), 11 deletions(-)

    --- a/drivers/net/bonding/bond_main.c
    +++ b/drivers/net/bonding/bond_main.c
    @@ -214,6 +214,8 @@ static void bond_uninit(struct net_devic
    static struct rtnl_link_stats64 *bond_get_stats(struct net_device *bond_dev,
    struct rtnl_link_stats64 *stats);
    static void bond_slave_arr_handler(struct work_struct *work);
    +static bool bond_time_in_interval(struct bonding *bond, unsigned long last_act,
    + int mod);

    /*---------------------------- General routines -----------------------------*/

    @@ -2418,7 +2420,7 @@ int bond_arp_rcv(const struct sk_buff *s
    struct slave *slave)
    {
    struct arphdr *arp = (struct arphdr *)skb->data;
    - struct slave *curr_active_slave;
    + struct slave *curr_active_slave, *curr_arp_slave;
    unsigned char *arp_ptr;
    __be32 sip, tip;
    int alen, is_arp = skb->protocol == __cpu_to_be16(ETH_P_ARP);
    @@ -2465,26 +2467,41 @@ int bond_arp_rcv(const struct sk_buff *s
    &sip, &tip);

    curr_active_slave = rcu_dereference(bond->curr_active_slave);
    + curr_arp_slave = rcu_dereference(bond->current_arp_slave);

    - /* Backup slaves won't see the ARP reply, but do come through
    - * here for each ARP probe (so we swap the sip/tip to validate
    - * the probe). In a "redundant switch, common router" type of
    - * configuration, the ARP probe will (hopefully) travel from
    - * the active, through one switch, the router, then the other
    - * switch before reaching the backup.
    + /* We 'trust' the received ARP enough to validate it if:
    *
    - * We 'trust' the arp requests if there is an active slave and
    - * it received valid arp reply(s) after it became active. This
    - * is done to avoid endless looping when we can't reach the
    + * (a) the slave receiving the ARP is active (which includes the
    + * current ARP slave, if any), or
    + *
    + * (b) the receiving slave isn't active, but there is a currently
    + * active slave and it received valid arp reply(s) after it became
    + * the currently active slave, or
    + *
    + * (c) there is an ARP slave that sent an ARP during the prior ARP
    + * interval, and we receive an ARP reply on any slave. We accept
    + * these because switch FDB update delays may deliver the ARP
    + * reply to a slave other than the sender of the ARP request.
    + *
    + * Note: for (b), backup slaves are receiving the broadcast ARP
    + * request, not a reply. This request passes from the sending
    + * slave through the L2 switch(es) to the receiving slave. Since
    + * this is checking the request, sip/tip are swapped for
    + * validation.
    + *
    + * This is done to avoid endless looping when we can't reach the
    * arp_ip_target and fool ourselves with our own arp requests.
    */
    -
    if (bond_is_active_slave(slave))
    bond_validate_arp(bond, slave, sip, tip);
    else if (curr_active_slave &&
    time_after(slave_last_rx(bond, curr_active_slave),
    curr_active_slave->last_link_up))
    bond_validate_arp(bond, slave, tip, sip);
    + else if (curr_arp_slave && (arp->ar_op == htons(ARPOP_REPLY)) &&
    + bond_time_in_interval(bond,
    + dev_trans_start(curr_arp_slave->dev), 1))
    + bond_validate_arp(bond, slave, sip, tip);

    out_unlock:
    if (arp != (struct arphdr *)skb->data)
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