Re: [Bridge] [PATCH net] net: bridge: mcast: Do not allow users to set IGMP counter/timer to zero

[Nikolay Aleksandrov <nikolay@nvidia.com>]

On 19/10/2021 08:43, Hangbin Liu wrote:
> Hi Nikolay,
> 
> On Mon, Oct 18, 2021 at 01:28:14PM +0300, Nikolay Aleksandrov wrote:
>> On 18/10/2021 11:26, Hangbin Liu wrote:
>>> There is no meaning to set an IGMP counter/timer to 0. Or it will cause
>>> unexpected behavior. E.g. if set multicast_membership_interval to 0,
>>> bridge will remove the mdb immediately after adding.
>>>
>>> Fixes: 79b859f573d6 ("bridge: netlink: add support for multicast_last_member_count")
>>> Fixes: b89e6babad4b ("bridge: netlink: add support for multicast_startup_query_count")
>>> Fixes: 7e4df51eb35d ("bridge: netlink: add support for igmp's intervals")
>>> Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
>>> ---
>>>  net/bridge/br_netlink.c  | 73 +++++++++++++++++++++++++++++---------
>>>  net/bridge/br_sysfs_br.c | 75 +++++++++++++++++++++++++++++++---------
>>>  2 files changed, 116 insertions(+), 32 deletions(-)
>>>
>>
>> Nacked-by: Nikolay Aleksandrov <nikolay@nvidia.com>
>>
>> For a few reasons,
>> I'll start with the obvious that - yes, users are allowed to change the values to non-RFC
>> compliant, but we cannot change that now as we'd risk breaking user-space which is probably
>> doing that somewhere with some of the values below. We can fix any issues that might arise
>> from doing it though, so it doesn't affect normal operation. If changing some of the options
>> to 0 or to unreasonably high values lead to problems let's fix those and we could discuss
>> adding constraints there if necessary.
> 
> I started this patch when I saw there is not limit for setting
> multicast_membership_interval to 0, which will cause bridge remove the
> mdb directly after adding. Do you think this is a problem.
> 
> And what about others? I don't think there is a meaning to set other intervals
> to 0.
> 

The problem is not if there is meaning, we cannot start restricting option values now after
they've become uapi (and have been for a very long time) because we can break user-space even
though chances are pretty low. I don't think this patch is acceptable, I commented on the other
patch issues but they don't matter because of this.

Thanks,
 Nik