Subject: Re: [patch net/stable v2] br: fix use of ->rx_handler_data in code executed on non-rx_handler path

From: Vlad Yasevich <[email-masked]>
Date: Fri, 06 Dec 2013 20:44:11 -0500

On 12/05/2013 09:26 PM, Gao feng wrote:
> On 12/06/2013 12:55 AM, Stephen Hemminger wrote:
>> On Thu,  5 Dec 2013 16:27:37 +0100
>> Jiri Pirko <[email-masked]> wrote:
>>
>>> br_stp_rcv() is reached by non-rx_handler path. That means there is no
>>> guarantee that dev is bridge port and therefore simple NULL check of
>>> ->rx_handler_data is not enough. There is need to check if dev is really
>>> bridge port and since only rcu read lock is held here, do it by checking
>>> ->rx_handler pointer.
>>>
>>> Note that synchronize_net() in netdev_rx_handler_unregister() ensures
>>> this approach as valid.
>>>
>>
>>
>> I think this patch is simpler/better, it restores the old logic.
>>
>> Ps. submitting patches to bugzilla is a good way to have them ignored.
>>
>> >From Stephen Hemminger <[email-masked]>
>>
>> Check that incoming STP packet is received on a port assigned to bridge
>> before processing. It is possible to receive packet on non-bridge port
>> because they are multicast.
>>
>> See:
>>  https://bugzilla.kernel.org/show_bug.cgi?id=64911
>>
>>
>> Regression introduced by:
>> commit 716ec052d2280d511e10e90ad54a86f5b5d4dcc2
>> Author: Hong Zhiguo <[email-masked]>
>> Date:   Sat Sep 14 22:42:28 2013 +0800
>>
>>     bridge: fix NULL pointer deref of br_port_get_rcu
>>
>>
>> Reported-by: Alexander Y. Fomichev
>> Signed-off-by: Stephen Hemminger <[email-masked]>
>>
>>
>> --- a/net/bridge/br_stp_bpdu.c	2013-06-11 09:50:21.522919061 -0700
>> +++ b/net/bridge/br_stp_bpdu.c	2013-12-05 08:46:56.090463702 -0800
>> @@ -153,6 +153,9 @@ void br_stp_rcv(const struct stp_proto *
>>  	if (buf[0] != 0 || buf[1] != 0 || buf[2] != 0)
>>  		goto err;
>>  
>> +	if (!br_port_exists(dev))
>> +		goto err;
>> +
>>  	p = br_port_get_rcu(dev);
>>  	if (!p)
>>  		goto err;
> 
> 
> We alreay did some cleanup jobs before mark this dev is not a port of bridge (dev->priv_flags &= ~IFF_BRIDGE_PORT),
> such as remove the fdb related to this port(br_fdb_delete_by_port).
> 
> and seems like after these cleanup jobs, before unregister this device, if new skb is received,
> br_handle_local_finish will call br_fdb_update to create a new fdb whose dst points to the will-be-destroied-port.

Not really.  We disable the port first before removing the fdb
as a result, br_handle_local_finish() will not update the fdb because
the port is in disabled state.

-vlad

> 
> I don't know if this will cause some problems.
> seems we should also make sure port is unavailable before we do cleanup.
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