Subject: Re: [PATCH net-next v2] bridge: set is_local and is_static before fdb entry is added to the fdb hashtable

From: roopa <[email-masked]>
Date: Tue, 27 Oct 2015 07:55:30 -0700

On 10/27/15, 7:02 AM, David Miller wrote:
> From: Nikolay Aleksandrov <[email-masked]>
> Date: Tue, 27 Oct 2015 14:31:48 +0100
>
>> On 10/27/2015 01:12 PM, Roopa Prabhu wrote:
>>> From: Roopa Prabhu <[email-masked]>
>>>
>>> Problem Description:
>>> We can add fdbs pointing to the bridge with NULL ->dst but that has a
>>> few race conditions because br_fdb_insert() is used which first creates
>>> the fdb and then, after the fdb has been published/linked, sets
>>> "is_local" to 1 and in that time frame if a packet arrives for that fdb
>>> it may see it as non-local and either do a NULL ptr dereference in
>>> br_forward() or attach the fdb to the port where it arrived, and later
>>> br_fdb_insert() will make it local thus getting a wrong fdb entry.
>>> Call chain br_handle_frame_finish() -> br_forward():
>>> But in br_handle_frame_finish() in order to call br_forward() the dst
>>> should not be local i.e. skb != NULL, whenever the dst is
>>> found to be local skb is set to NULL so we can't forward it,
>>> and here comes the problem since it's running only
>>> with RCU when forwarding packets it can see the entry before "is_local"
>>> is set to 1 and actually try to dereference NULL.
>>> The main issue is that if someone sends a packet to the switch while
>>> it's adding the entry which points to the bridge device, it may
>>> dereference NULL ptr. This is needed now after we can add fdbs
>>> pointing to the bridge.  This poses a problem for
>>> br_fdb_update() as well, while someone's adding a bridge fdb, but
>>> before it has is_local == 1, it might get moved to a port if it comes
>>> as a source mac and then it may get its "is_local" set to 1
>>>
>>> This patch changes fdb_create to take is_local and is_static as
>>> arguments to set these values in the fdb entry before it is added to the
>>> hash. Also adds null check for port in br_forward.
>>>
>>> Reported-by: Nikolay Aleksandrov <[email-masked]>
>>> Signed-off-by: Roopa Prabhu <[email-masked]>
>>> ---
>>> v2 - fix compile error reported by kbuild test robot.
>>>      Accidently i had posted an older version of the patch
>>>
>> Thanks for fixing this,
>>
>> Fixes: 3741873b4f73 ("bridge: allow adding of fdb entries pointing to the bridge device")
>> Reviewed-by: Nikolay Aleksandrov <[email-masked]>
> This still doesn't compile:
>
> net/bridge/br_fdb.c: In function ‘br_fdb_external_learn_add’:
> net/bridge/br_fdb.c:1103:3: error: too few arguments to function ‘fdb_create’
> net/bridge/br_fdb.c:495:37: note: declared here
sorry david about the sloppiness. Resent. There was a problem with my patch generation.