Subject: Re: [PATCHv2 net] bridge: move bridge multicast cleanup to ndo_uninit

From: Stephen Hemminger <[email-masked]>
Date: Tue, 25 Apr 2017 09:41:27 -0700

On Tue, 25 Apr 2017 22:58:37 +0800
Xin Long <[email-masked]> wrote:

> 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.
> 
> Reported-by: Jianwen Ji <[email-masked]>
> Signed-off-by: Xin Long <[email-masked]>

Makes sense.

Reviewed-by: Stephen Hemminger <[email-masked]>