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Message-ID: <fb2a9ee9-ff66-3590-9aa9-88f5b037d786@blackwall.org>
Date: Fri, 3 Feb 2023 10:59:25 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Petr Machata <petrm@...dia.com>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Roopa Prabhu <roopa@...dia.com>, netdev@...r.kernel.org
Cc: bridge@...ts.linux-foundation.org, Ido Schimmel <idosch@...dia.com>
Subject: Re: [PATCH net-next v3 07/16] net: bridge: Maintain number of MDB
entries in net_bridge_mcast_port
On 02/02/2023 19:59, Petr Machata wrote:
> The MDB maintained by the bridge is limited. When the bridge is configured
> for IGMP / MLD snooping, a buggy or malicious client can easily exhaust its
> capacity. In SW datapath, the capacity is configurable through the
> IFLA_BR_MCAST_HASH_MAX parameter, but ultimately is finite. Obviously a
> similar limit exists in the HW datapath for purposes of offloading.
>
> In order to prevent the issue of unilateral exhaustion of MDB resources,
> introduce two parameters in each of two contexts:
>
> - Per-port and per-port-VLAN number of MDB entries that the port
> is member in.
>
> - Per-port and (when BROPT_MCAST_VLAN_SNOOPING_ENABLED is enabled)
> per-port-VLAN maximum permitted number of MDB entries, or 0 for
> no limit.
>
> The per-port multicast context is used for tracking of MDB entries for the
> port as a whole. This is available for all bridges.
>
> The per-port-VLAN multicast context is then only available on
> VLAN-filtering bridges on VLANs that have multicast snooping on.
>
> With these changes in place, it will be possible to configure MDB limit for
> bridge as a whole, or any one port as a whole, or any single port-VLAN.
>
> Note that unlike the global limit, exhaustion of the per-port and
> per-port-VLAN maximums does not cause disablement of multicast snooping.
> It is also permitted to configure the local limit larger than hash_max,
> even though that is not useful.
>
> In this patch, introduce only the accounting for number of entries, and the
> max field itself, but not the means to toggle the max. The next patch
> introduces the netlink APIs to toggle and read the values.
>
> Signed-off-by: Petr Machata <petrm@...dia.com>
> ---
>
> Notes:
> v3:
> - Access mdb_max_/_n_entries through READ_/WRITE_ONCE
> - Move extack setting to br_multicast_port_ngroups_inc_one().
> Since we use NL_SET_ERR_MSG_FMT_MOD, the correct context
> (port / port-vlan) can be passed through an argument.
> This also removes the need for more READ/WRITE_ONCE's
> at the extack-setting site.
>
> v2:
> - In br_multicast_port_ngroups_inc_one(), bounce
> if n>=max, not if n==max
> - Adjust extack messages to mention ngroups, now that
> the bounces appear when n>=max, not n==max
> - In __br_multicast_enable_port_ctx(), do not reset
> max to 0. Also do not count number of entries by
> going through _inc, as that would end up incorrectly
> bouncing the entries.
>
> net/bridge/br_multicast.c | 136 +++++++++++++++++++++++++++++++++++++-
> net/bridge/br_private.h | 2 +
> 2 files changed, 137 insertions(+), 1 deletion(-)
Acked-by: Nikolay Aleksandrov <razor@...ckwall.org>
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