net: bridge: mst: pass vlan group directly to br_mst_vlan_set_state

Pass the already obtained vlan group pointer to br_mst_vlan_set_state()
instead of dereferencing it again. Each caller has already correctly
dereferenced it for their context. This change is required for the
following suspicious RCU dereference fix. No functional changes
intended.

Fixes: 3a7c1661 ("net: bridge: mst: fix vlan use-after-free")
Reported-by: syzbot+9bbe2de1bc9d470eb5fe@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=9bbe2de1bc9d470eb5feSigned-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Link: https://lore.kernel.org/r/20240609103654.914987-2-razor@blackwall.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/bridge/br_mst.c

@@ -73,11 +73,10 @@ int br_mst_get_state(const struct net_device *dev, u16 msti, u8 *state)
 }
 EXPORT_SYMBOL_GPL(br_mst_get_state);
 
-static void br_mst_vlan_set_state(struct net_bridge_port *p, struct net_bridge_vlan *v,
+static void br_mst_vlan_set_state(struct net_bridge_vlan_group *vg,
+				  struct net_bridge_vlan *v,
 				  u8 state)
 {
-	struct net_bridge_vlan_group *vg = nbp_vlan_group(p);
-
 	if (br_vlan_get_state(v) == state)
 		return;
 
@@ -121,7 +120,7 @@ int br_mst_set_state(struct net_bridge_port *p, u16 msti, u8 state,
 		if (v->brvlan->msti != msti)
 			continue;
 
-		br_mst_vlan_set_state(p, v, state);
+		br_mst_vlan_set_state(vg, v, state);
 	}
 
 out:
@@ -140,13 +139,13 @@ static void br_mst_vlan_sync_state(struct net_bridge_vlan *pv, u16 msti)
 		 * it.
 		 */
 		if (v != pv && v->brvlan->msti == msti) {
-			br_mst_vlan_set_state(pv->port, pv, v->state);
+			br_mst_vlan_set_state(vg, pv, v->state);
 			return;
 		}
 	}
 
 	/* Otherwise, start out in a new MSTI with all ports disabled. */
-	return br_mst_vlan_set_state(pv->port, pv, BR_STATE_DISABLED);
+	return br_mst_vlan_set_state(vg, pv, BR_STATE_DISABLED);
 }
 
 int br_mst_vlan_set_msti(struct net_bridge_vlan *mv, u16 msti)