bridge: mdb: Allow replace of a host-joined group

JIRA: https://issues.redhat.com/browse/RHEL-75595

commit d9e9f6d
Author: Petr Machata <[email protected]>
Date:   Tue Feb 4 18:37:15 2025 +0100

    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 <[email protected]>
    Reviewed-by: Ido Schimmel <[email protected]>
    Acked-by: Nikolay Aleksandrov <[email protected]>
    Link: https://patch.msgid.link/e5c5188b9787ae806609e7ca3aa2a0a501b9b5c4.1738685648.git.petrm@nvidia.com
    Signed-off-by: Jakub Kicinski <[email protected]>

Signed-off-by: Mohammad Heib <[email protected]>

Author: mohammadheib

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;
 		}

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