netdev - Re: [PATCH net] bridge: shutdown bridge device before removing it

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Date:   Mon, 24 Apr 2017 14:29:12 +0300
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     Xin Long <lucien.xin@...il.com>,
        network dev <netdev@...r.kernel.org>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "bridge@...ts.linux-foundation.org" 
        <bridge@...ts.linux-foundation.org>
Subject: Re: [PATCH net] bridge: shutdown bridge device before removing it

On 24/04/17 14:01, Nikolay Aleksandrov wrote:
> On 24/04/17 10:25, Xin Long 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.
>> This can happen when ip link remove a bridge or destroy a netns with a
>> bridge device inside.
>>
>> As we can see in br_del_bridge, brctl is also supposed to remove a bridge
>> device after it's shutdown.
>>
>> This patch is to call dev_close at the beginning of br_dev_delete so that
>> netif_running check in br_multicast_add_group can avoid this issue. But
>> to keep consistent with before, it will not remove the IFF_UP check in
>> br_del_bridge for brctl.
>>
>> Reported-by: Jianwen Ji <jiji@...hat.com>
>> Signed-off-by: Xin Long <lucien.xin@...il.com>
>> ---
>>  net/bridge/br_if.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
> 
> +CC bridge maintainers
> 
> I can see how this could happen, could you also provide the traceback ?
> 
> The patch looks good to me, actually I think it fixes another issue with
> mcast stats where the percpu pointer can be accessed after it's freed if
> an mcast packet can get sent via br->dev after the br_multicast_dev_del() call.

Never mind the another issue part, Ido's recent ndo_uninit() patch fixed it.

> This is definitely stable material, if I'm not mistaken the issue is there since
> the introduction of br_dev_delete:
> commit e10177abf842
> Author: Satish Ashok <sashok@...ulusnetworks.com>
> Date:   Wed Jul 15 07:16:51 2015 -0700
> 
>     bridge: multicast: fix handling of temp and perm entries
> 
> 
> 
> Acked-by: Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
> 
> 
> 
> 
> 
> 
>