netdev - Re: [PATCH net] net: netlink: cap max groups which will be considered in netlink

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Message-ID: <509c952b-483f-3a35-6d6b-4655a8b513be@cumulusnetworks.com>
Date:   Fri, 21 Feb 2020 10:31:17 +0200
From:   Nikolay Aleksandrov <nikolay@...ulusnetworks.com>
To:     David Ahern <dsahern@...il.com>, David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, christophe.leroy@....fr, rgb@...hat.com,
        erhard_f@...lbox.org
Subject: Re: [PATCH net] net: netlink: cap max groups which will be considered
 in netlink_bind()

On 21/02/2020 04:55, David Ahern wrote:
> On 2/20/20 5:02 PM, David Miller wrote:
>>
>>> Dave it is not necessary to queue this fix for stable releases since
>>> NETLINK_ROUTE is the first to reach more groups after I added the vlan
>>> notification changes and I don't think we'll ever backport new groups. :)
>>> Up to you of course.
> 
> RTNLGRP_NEXTHOP was the first to overflow; RTNLGRP_NEXTHOP = 32.
> 
> Apparently my comment about overflowing the groups was only in the
> iproute2 commit (e7cd93e7afe1a0407ccb94b9124bbd56b87b8660)
> 

While that is true, RTNLGRP_MAX == (__RTNLGRP_MAX - 1) == RTNLGRP_NEXTHOP == 32
which is fine. You just can't bind to the group via netlink_bind() but the loop
is capped at 32 again and the test_bit() shouldn't access anything beyond because
it's a strict less than.