Linux Ethernet Bridging - Oct 2021 - [Bridge] [PATCH net] net: bridge: mcast: Do not allow users to set IGMP counter/timer to zero

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 at 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 at 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

On Tue, Oct 19, 2021 at 07:09:42PM +0300, Nikolay Aleksandrov
wrote:
> > 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.
OK, I got your mean, we should not restrict the configurations based on whether
there is a meaning.

Thanks
Hangbin