mwifiex: fixup error cases in mwifiex_add_virtual_intf()

If we fail to add an interface in mwifiex_add_virtual_intf(), we might
hit a BUG_ON() in the networking code, because we didn't tear things
down properly. Among the problems:

 (a) when failing to allocate workqueues, we fail to unregister the
     netdev before calling free_netdev()
 (b) even if we do try to unregister the netdev, we're still holding the
     rtnl lock, so the device never properly unregistered; we'll be at
     state NETREG_UNREGISTERING, and then hit free_netdev()'s:
	BUG_ON(dev->reg_state != NETREG_UNREGISTERED);
 (c) we're allocating some dependent resources (e.g., DFS workqueues)
     after we've registered the interface; this may or may not cause
     problems, but it's good practice to allocate these before registering
 (d) we're not even trying to unwind anything when mwifiex_send_cmd() or
     mwifiex_sta_init_cmd() fail

To fix these issues, let's:

 * add a stacked set of error handling labels, to keep error handling
   consistent and properly ordered (resolving (a) and (d))
 * move the workqueue allocations before the registration (to resolve
   (c); also resolves (b) by avoiding error cases where we have to
   unregister)

[Incidentally, it's pretty easy to interrupt the alloc_workqueue() in,
e.g., the following:

  iw phy phy0 interface add mlan0 type station

by sending it SIGTERM.]

This bugfix covers commits like commit 7d652034 ("mwifiex: channel
switch support for mwifiex"), but parts of this bug exist all the way
back to the introduction of dynamic interface handling in commit
93a1df48 ("mwifiex: add cfg80211 handlers add/del_virtual_intf").

Cc: <stable@vger.kernel.org>
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/marvell/mwifiex/cfg80211.c

@@ -2964,10 +2964,8 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 	if (!dev) {
 		mwifiex_dbg(adapter, ERROR,
 			    "no memory available for netdevice\n");
-		memset(&priv->wdev, 0, sizeof(priv->wdev));
-		priv->wdev.iftype = NL80211_IFTYPE_UNSPECIFIED;
-		priv->bss_mode = NL80211_IFTYPE_UNSPECIFIED;
-		return ERR_PTR(-ENOMEM);
+		ret = -ENOMEM;
+		goto err_alloc_netdev;
 	}
 
 	mwifiex_init_priv_params(priv, dev);
@@ -2976,11 +2974,11 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 	ret = mwifiex_send_cmd(priv, HostCmd_CMD_SET_BSS_MODE,
 			       HostCmd_ACT_GEN_SET, 0, NULL, true);
 	if (ret)
-		return ERR_PTR(ret);
+		goto err_set_bss_mode;
 
 	ret = mwifiex_sta_init_cmd(priv, false, false);
 	if (ret)
-		return ERR_PTR(ret);
+		goto err_sta_init;
 
 	mwifiex_setup_ht_caps(&wiphy->bands[NL80211_BAND_2GHZ]->ht_cap, priv);
 	if (adapter->is_hw_11ac_capable)
@@ -3011,31 +3009,14 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 
 	SET_NETDEV_DEV(dev, adapter->dev);
 
-	/* Register network device */
-	if (register_netdevice(dev)) {
-		mwifiex_dbg(adapter, ERROR,
-			    "cannot register virtual network device\n");
-		free_netdev(dev);
-		priv->bss_mode = NL80211_IFTYPE_UNSPECIFIED;
-		priv->netdev = NULL;
-		memset(&priv->wdev, 0, sizeof(priv->wdev));
-		priv->wdev.iftype = NL80211_IFTYPE_UNSPECIFIED;
-		return ERR_PTR(-EFAULT);
-	}
-
 	priv->dfs_cac_workqueue = alloc_workqueue("MWIFIEX_DFS_CAC%s",
 						  WQ_HIGHPRI |
 						  WQ_MEM_RECLAIM |
 						  WQ_UNBOUND, 1, name);
 	if (!priv->dfs_cac_workqueue) {
-		mwifiex_dbg(adapter, ERROR,
-			    "cannot register virtual network device\n");
-		free_netdev(dev);
-		priv->bss_mode = NL80211_IFTYPE_UNSPECIFIED;
-		priv->netdev = NULL;
-		memset(&priv->wdev, 0, sizeof(priv->wdev));
-		priv->wdev.iftype = NL80211_IFTYPE_UNSPECIFIED;
-		return ERR_PTR(-ENOMEM);
+		mwifiex_dbg(adapter, ERROR, "cannot alloc DFS CAC queue\n");
+		ret = -ENOMEM;
+		goto err_alloc_cac;
 	}
 
 	INIT_DELAYED_WORK(&priv->dfs_cac_work, mwifiex_dfs_cac_work_queue);
@@ -3044,16 +3025,9 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 						      WQ_HIGHPRI | WQ_UNBOUND |
 						      WQ_MEM_RECLAIM, 1, name);
 	if (!priv->dfs_chan_sw_workqueue) {
-		mwifiex_dbg(adapter, ERROR,
-			    "cannot register virtual network device\n");
-		free_netdev(dev);
-		priv->bss_mode = NL80211_IFTYPE_UNSPECIFIED;
-		priv->netdev = NULL;
-		memset(&priv->wdev, 0, sizeof(priv->wdev));
-		priv->wdev.iftype = NL80211_IFTYPE_UNSPECIFIED;
-		destroy_workqueue(priv->dfs_cac_workqueue);
-		priv->dfs_cac_workqueue = NULL;
-		return ERR_PTR(-ENOMEM);
+		mwifiex_dbg(adapter, ERROR, "cannot alloc DFS channel sw queue\n");
+		ret = -ENOMEM;
+		goto err_alloc_chsw;
 	}
 
 	INIT_DELAYED_WORK(&priv->dfs_chan_sw_work,
@@ -3061,6 +3035,13 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 
 	sema_init(&priv->async_sem, 1);
 
+	/* Register network device */
+	if (register_netdevice(dev)) {
+		mwifiex_dbg(adapter, ERROR, "cannot register network device\n");
+		ret = -EFAULT;
+		goto err_reg_netdev;
+	}
+
 	mwifiex_dbg(adapter, INFO,
 		    "info: %s: Marvell 802.11 Adapter\n", dev->name);
 
@@ -3081,11 +3062,29 @@ struct wireless_dev *mwifiex_add_virtual_intf(struct wiphy *wiphy,
 		adapter->curr_iface_comb.p2p_intf++;
 		break;
 	default:
+		/* This should be dead code; checked above */
 		mwifiex_dbg(adapter, ERROR, "type not supported\n");
 		return ERR_PTR(-EINVAL);
 	}
 
 	return &priv->wdev;
+
+err_reg_netdev:
+	destroy_workqueue(priv->dfs_chan_sw_workqueue);
+	priv->dfs_chan_sw_workqueue = NULL;
+err_alloc_chsw:
+	destroy_workqueue(priv->dfs_cac_workqueue);
+	priv->dfs_cac_workqueue = NULL;
+err_alloc_cac:
+	free_netdev(dev);
+	priv->netdev = NULL;
+err_sta_init:
+err_set_bss_mode:
+err_alloc_netdev:
+	memset(&priv->wdev, 0, sizeof(priv->wdev));
+	priv->wdev.iftype = NL80211_IFTYPE_UNSPECIFIED;
+	priv->bss_mode = NL80211_IFTYPE_UNSPECIFIED;
+	return ERR_PTR(ret);
 }
 EXPORT_SYMBOL_GPL(mwifiex_add_virtual_intf);