During removing a bridge device, if the bridge is still up, a new mdb entry
still can be added in br_multicast_add_group() after all mdb entries are
removed in br_multicast_dev_del(). Like the path:

  mld_ifc_timer_expire ->
    mld_sendpack -> ...
      br_multicast_rcv ->
        br_multicast_add_group

The new mp's timer will be set up. If the timer expires after the bridge
is freed, it may cause use-after-free panic in br_multicast_group_expired.

BUG: unable to handle kernel NULL pointer dereference at 0000000000000048
IP: [<ffffffffa07ed2c8>] br_multicast_group_expired+0x28/0xb0 [bridge]
Call Trace:
 <IRQ>
 [<ffffffff81094536>] call_timer_fn+0x36/0x110
 [<ffffffffa07ed2a0>] ? br_mdb_free+0x30/0x30 [bridge]
 [<ffffffff81096967>] run_timer_softirq+0x237/0x340
 [<ffffffff8108dcbf>] __do_softirq+0xef/0x280
 [<ffffffff8169889c>] call_softirq+0x1c/0x30
 [<ffffffff8102c275>] do_softirq+0x65/0xa0
 [<ffffffff8108e055>] irq_exit+0x115/0x120
 [<ffffffff81699515>] smp_apic_timer_interrupt+0x45/0x60
 [<ffffffff81697a5d>] apic_timer_interrupt+0x6d/0x80

Nikolay also found it would cause a memory leak - the mdb hash is
reallocated and not freed due to the mdb rehash.

unreferenced object 0xffff8800540ba800 (size 2048):
  backtrace:
    [<ffffffff816e2287>] kmemleak_alloc+0x67/0xc0
    [<ffffffff81260bea>] __kmalloc+0x1ba/0x3e0
    [<ffffffffa05c60ee>] br_mdb_rehash+0x5e/0x340 [bridge]
    [<ffffffffa05c74af>] br_multicast_new_group+0x43f/0x6e0 [bridge]
    [<ffffffffa05c7aa3>] br_multicast_add_group+0x203/0x260 [bridge]
    [<ffffffffa05ca4b5>] br_multicast_rcv+0x945/0x11d0 [bridge]
    [<ffffffffa05b6b10>] br_dev_xmit+0x180/0x470 [bridge]
    [<ffffffff815c781b>] dev_hard_start_xmit+0xbb/0x3d0
    [<ffffffff815c8743>] __dev_queue_xmit+0xb13/0xc10
    [<ffffffff815c8850>] dev_queue_xmit+0x10/0x20
    [<ffffffffa02f8d7a>] ip6_finish_output2+0x5ca/0xac0 [ipv6]
    [<ffffffffa02fbfc6>] ip6_finish_output+0x126/0x2c0 [ipv6]
    [<ffffffffa02fc245>] ip6_output+0xe5/0x390 [ipv6]
    [<ffffffffa032b92c>] NF_HOOK.constprop.44+0x6c/0x240 [ipv6]
    [<ffffffffa032bd16>] mld_sendpack+0x216/0x3e0 [ipv6]
    [<ffffffffa032d5eb>] mld_ifc_timer_expire+0x18b/0x2b0 [ipv6]

This could happen when ip link remove a bridge or destroy a netns with a
bridge device inside.

With Nikolay's suggestion, this patch is to clean up bridge multicast in
ndo_uninit after bridge dev is shutdown, instead of br_dev_delete, so
that netif_running check in br_multicast_add_group can avoid this issue.

v1->v2:
  - fix this issue by moving br_multicast_dev_del to ndo_uninit, instead
    of calling dev_close in br_dev_delete.

(NOTE: Depends upon b6fe0440 ("bridge: implement missing ndo_uninit()"))

Fixes: e10177ab ("bridge: multicast: fix handling of temp and perm entries")
Reported-by: Jianwen Ji <jiji@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>