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    Subject[PATCH 3.16 134/148] net: bridge: deny dev_set_mac_address() when unregistering
    3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>

    commit c4b4c421857dc7b1cf0dccbd738472360ff2cd70 upstream.

    We have an interesting memory leak in the bridge when it is being
    unregistered and is a slave to a master device which would change the
    mac of its slaves on unregister (e.g. bond, team). This is a very
    unusual setup but we do end up leaking 1 fdb entry because
    dev_set_mac_address() would cause the bridge to insert the new mac address
    into its table after all fdbs are flushed, i.e. after dellink() on the
    bridge has finished and we call NETDEV_UNREGISTER the bond/team would
    release it and will call dev_set_mac_address() to restore its original
    address and that in turn will add an fdb in the bridge.
    One fix is to check for the bridge dev's reg_state in its
    ndo_set_mac_address callback and return an error if the bridge is not in
    NETREG_REGISTERED.

    Easy steps to reproduce:
    1. add bond in mode != A/B
    2. add any slave to the bond
    3. add bridge dev as a slave to the bond
    4. destroy the bridge device

    Trace:
    unreferenced object 0xffff888035c4d080 (size 128):
    comm "ip", pid 4068, jiffies 4296209429 (age 1413.753s)
    hex dump (first 32 bytes):
    41 1d c9 36 80 88 ff ff 00 00 00 00 00 00 00 00 A..6............
    d2 19 c9 5e 3f d7 00 00 00 00 00 00 00 00 00 00 ...^?...........
    backtrace:
    [<00000000ddb525dc>] kmem_cache_alloc+0x155/0x26f
    [<00000000633ff1e0>] fdb_create+0x21/0x486 [bridge]
    [<0000000092b17e9c>] fdb_insert+0x91/0xdc [bridge]
    [<00000000f2a0f0ff>] br_fdb_change_mac_address+0xb3/0x175 [bridge]
    [<000000001de02dbd>] br_stp_change_bridge_id+0xf/0xff [bridge]
    [<00000000ac0e32b1>] br_set_mac_address+0x76/0x99 [bridge]
    [<000000006846a77f>] dev_set_mac_address+0x63/0x9b
    [<00000000d30738fc>] __bond_release_one+0x3f6/0x455 [bonding]
    [<00000000fc7ec01d>] bond_netdev_event+0x2f2/0x400 [bonding]
    [<00000000305d7795>] notifier_call_chain+0x38/0x56
    [<0000000028885d4a>] call_netdevice_notifiers+0x1e/0x23
    [<000000008279477b>] rollback_registered_many+0x353/0x6a4
    [<0000000018ef753a>] unregister_netdevice_many+0x17/0x6f
    [<00000000ba854b7a>] rtnl_delete_link+0x3c/0x43
    [<00000000adf8618d>] rtnl_dellink+0x1dc/0x20a
    [<000000009b6395fd>] rtnetlink_rcv_msg+0x23d/0x268

    Fixes: 43598813386f ("bridge: add local MAC address to forwarding table (v2)")
    Reported-by: syzbot+2add91c08eb181fea1bf@syzkaller.appspotmail.com
    Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    net/bridge/br_device.c | 6 ++++++
    1 file changed, 6 insertions(+)

    --- a/net/bridge/br_device.c
    +++ b/net/bridge/br_device.c
    @@ -193,6 +193,12 @@ static int br_set_mac_address(struct net
    if (!is_valid_ether_addr(addr->sa_data))
    return -EADDRNOTAVAIL;

    + /* dev_set_mac_addr() can be called by a master device on bridge's
    + * NETDEV_UNREGISTER, but since it's being destroyed do nothing
    + */
    + if (dev->reg_state != NETREG_REGISTERED)
    + return -EBUSY;
    +
    spin_lock_bh(&br->lock);
    if (!ether_addr_equal(dev->dev_addr, addr->sa_data)) {
    /* Mac address will be changed in br_stp_change_bridge_id(). */
    \
     
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