netdev - [PATCH net-next] bridge: mdb: Allow replace of a host-joined group

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Message-ID: <e5c5188b9787ae806609e7ca3aa2a0a501b9b5c4.1738685648.git.petrm@nvidia.com>
Date: Tue, 4 Feb 2025 18:37:15 +0100
From: Petr Machata <petrm@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
	<netdev@...r.kernel.org>
CC: Roopa Prabhu <roopa@...dia.com>, Nikolay Aleksandrov
	<razor@...ckwall.org>, Ido Schimmel <idosch@...dia.com>, Petr Machata
	<petrm@...dia.com>, <bridge@...ts.linux.dev>, <mlxsw@...dia.com>
Subject: [PATCH net-next] bridge: mdb: Allow replace of a host-joined group

Attempts to replace an MDB group membership of the host itself are
currently bounced:

 # ip link add name br up type bridge vlan_filtering 1
 # bridge mdb replace dev br port br grp 239.0.0.1 vid 2
 # bridge mdb replace dev br port br grp 239.0.0.1 vid 2
 Error: bridge: Group is already joined by host.

A similar operation done on a member port would succeed. Ignore the check
for replacement of host group memberships as well.

The bit of code that this enables is br_multicast_host_join(), which, for
already-joined groups only refreshes the MC group expiration timer, which
is desirable; and a userspace notification, also desirable.

Change a selftest that exercises this code path from expecting a rejection
to expecting a pass. The rest of MDB selftests pass without modification.

Signed-off-by: Petr Machata <petrm@...dia.com>
Reviewed-by: Ido Schimmel <idosch@...dia.com>
---
 net/bridge/br_mdb.c                                  | 2 +-
 tools/testing/selftests/net/forwarding/bridge_mdb.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bridge/br_mdb.c b/net/bridge/br_mdb.c
index 1a52a0bca086..7e1ad229e133 100644
--- a/net/bridge/br_mdb.c
+++ b/net/bridge/br_mdb.c
@@ -1040,7 +1040,7 @@ static int br_mdb_add_group(const struct br_mdb_config *cfg,
 
 	/* host join */
 	if (!port) {
-		if (mp->host_joined) {
+		if (mp->host_joined && !(cfg->nlflags & NLM_F_REPLACE)) {
 			NL_SET_ERR_MSG_MOD(extack, "Group is already joined by host");
 			return -EEXIST;
 		}
diff --git a/tools/testing/selftests/net/forwarding/bridge_mdb.sh b/tools/testing/selftests/net/forwarding/bridge_mdb.sh
index d9d587454d20..8c1597ebc2d3 100755
--- a/tools/testing/selftests/net/forwarding/bridge_mdb.sh
+++ b/tools/testing/selftests/net/forwarding/bridge_mdb.sh
@@ -149,7 +149,7 @@ cfg_test_host_common()
 	check_err $? "Failed to add $name host entry"
 
 	bridge mdb replace dev br0 port br0 grp $grp $state vid 10 &> /dev/null
-	check_fail $? "Managed to replace $name host entry"
+	check_err $? "Failed to replace $name host entry"
 
 	bridge mdb del dev br0 port br0 grp $grp $state vid 10
 	bridge mdb get dev br0 grp $grp vid 10 &> /dev/null
-- 
2.47.0