netdev - Re: [PATCH net-next v2] net: ctnetlink: support filtering by zone

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Date: Fri, 2 Feb 2024 12:04:35 +0100
From: Ilya Maximets <i.maximets@....org>
To: Pablo Neira Ayuso <pablo@...filter.org>,
 Felix Huettner <felix.huettner@...l.schwarz>
Cc: linux-kernel@...r.kernel.org, netfilter-devel@...r.kernel.org,
 coreteam@...filter.org, netdev@...r.kernel.org,
 linux-kselftest@...r.kernel.org, kadlec@...filter.org, fw@...len.de,
 davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
 shuah@...nel.org, luca.czesla@...l.schwarz, max.lamprecht@...l.schwarz,
 i.maximets@....org, Simon Horman <horms@....org>
Subject: Re: [PATCH net-next v2] net: ctnetlink: support filtering by zone

On 12/22/23 13:01, Pablo Neira Ayuso wrote:
> On Mon, Nov 27, 2023 at 11:49:16AM +0000, Felix Huettner wrote:
>> conntrack zones are heavily used by tools like openvswitch to run
>> multiple virtual "routers" on a single machine. In this context each
>> conntrack zone matches to a single router, thereby preventing
>> overlapping IPs from becoming issues.
>> In these systems it is common to operate on all conntrack entries of a
>> given zone, e.g. to delete them when a router is deleted. Previously this
>> required these tools to dump the full conntrack table and filter out the
>> relevant entries in userspace potentially causing performance issues.
>>
>> To do this we reuse the existing CTA_ZONE attribute. This was previous
>> parsed but not used during dump and flush requests. Now if CTA_ZONE is
>> set we filter these operations based on the provided zone.
>> However this means that users that previously passed CTA_ZONE will
>> experience a difference in functionality.
>>
>> Alternatively CTA_FILTER could have been used for the same
>> functionality. However it is not yet supported during flush requests and
>> is only available when using AF_INET or AF_INET6.
> 
> For the record, this is applied to nf-next.

Hi, Felix and Pablo.

I was looking through the code and the following part is bothering me:

 diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
 index fb0ae15e96df..4e9133f61251 100644
 --- a/net/netfilter/nf_conntrack_netlink.c
 +++ b/net/netfilter/nf_conntrack_netlink.c
 @@ -1148,6 +1149,10 @@ static int ctnetlink_filter_match(struct nf_conn *ct, void *data)
         if (filter->family && nf_ct_l3num(ct) != filter->family)
                 goto ignore_entry;
 
 +       if (filter->zone.id != NF_CT_DEFAULT_ZONE_ID &&
 +           !nf_ct_zone_equal_any(ct, &filter->zone))
 +               goto ignore_entry;
 +
         if (filter->orig_flags) {
                 tuple = nf_ct_tuple(ct, IP_CT_DIR_ORIGINAL);
                 if (!ctnetlink_filter_match_tuple(&filter->orig, tuple,

If I'm reading that right, the default zone is always flushed, even if the
user requested to flush a different zone.  I.e. the entry is never ignored
for a default zone.  Is that correct or am I reading that wrong?

If my observation is correct, then I don't think this functionality can
actually be used by applications as it does something unexpected.

Best regards, Ilya Maximets.