bes2600: fix concurrency UAF in bes2600_hw_scan and sched_scan

bes2600_bss_info_changed() and bes2600_hw_scan() can run concurrently.
The probe-request SKB allocated by ieee80211_probereq_get() before
scan.lock + conf_lock are taken can be touched by a concurrent
bss_info_changed (via wsm_set_template_frame's path) while we hold no
lock.  Reorder to acquire both locks BEFORE the SKB allocation.

Also reorder cleanup paths so dev_kfree_skb() runs BEFORE up() —
otherwise a small window exists where the SKB has been touched but the
lock has been released, allowing concurrent code to also touch it.

Three sites fixed:
  - bes2600_hw_scan: lock-take + ENOMEM cleanup + wsm_set_template_frame
    error cleanup + success-path SKB free + lock release order
  - bes2600_sched_scan_start (#ifdef ROAM_OFFLOAD): same three sub-fixes
    (compiled-out at default build, fixed for consistency)
  - All success/error paths: dev_kfree_skb before up()

Backport of cw1200 mainline commit 86760e0dfe36 ("cw1200: Fix
concurrency use-after-free bugs in cw1200_hw_scan()", 2018-12-14),
which fixed the identical bug in the same code shape we inherited.
That commit was merged from upstream 4f68ef64cd7f.

Cherry-picked from upstream Linux:
  86760e0dfe36 cw1200: Fix concurrency use-after-free bugs in cw1200_hw_scan()
  Author: Jia-Ju Bai <baijiaju1990@gmail.com>
  Link: https://lore.kernel.org/r/20181214035521.7575-1-baijiaju1990@gmail.com

bes2600/bh.c

@@ -101,7 +101,7 @@ void bes2600_unregister_bh(struct bes2600_common *hw_priv)
 	coex_deinit_mode(hw_priv);
 #endif
 
-	atomic_add(1, &hw_priv->bh_term);
+	atomic_inc(&hw_priv->bh_term);
 	wake_up(&hw_priv->bh_wq);
 
 	flush_workqueue(hw_priv->bh_workqueue);
@@ -590,7 +590,7 @@ static int bes2600_bh(void *arg)
 			bes_devel("[BH] Device resume.\n");
 			atomic_set(&hw_priv->bh_suspend, BES2600_BH_RESUMED);
 			wake_up(&hw_priv->bh_evt_wq);
-			atomic_add(1, &hw_priv->bh_rx);
+			atomic_inc(&hw_priv->bh_rx);
 			continue;
 		}
 
@@ -758,9 +758,9 @@ tx:
 
 #if 0 /* count is not implemented */
 				if (ret > 1)
-					atomic_add(1, &hw_priv->bh_tx);
+					atomic_inc(&hw_priv->bh_tx);
 #else
-				atomic_add(1, &hw_priv->bh_tx);
+				atomic_inc(&hw_priv->bh_tx);
 #endif
 
 #if defined(CONFIG_BES2600_NON_POWER_OF_TWO_BLOCKSIZES)
@@ -1134,7 +1134,7 @@ static int bes2600_bh_tx_helper(struct bes2600_common *hw_priv,
 	tx_len += 4;
 #endif
 
-	atomic_add(1, &hw_priv->bh_tx);
+	atomic_inc(&hw_priv->bh_tx);
 
 	tx_len = hw_priv->sbus_ops->align_size(
 		hw_priv->sbus_priv, tx_len);
@@ -1435,7 +1435,7 @@ static int bes2600_bh(void *arg)
 			bes_devel("[BH] Device resume.\n");
 			atomic_set(&hw_priv->bh_suspend, BES2600_BH_RESUMED);
 			wake_up(&hw_priv->bh_evt_wq);
-			atomic_add(1, &hw_priv->bh_rx);
+			atomic_inc(&hw_priv->bh_rx);
 			goto done;
 		}
 

bes2600/itp.c

@@ -570,7 +570,7 @@ int bes2600_itp_get_tx(struct bes2600_common *priv, u8 **data,
 	*burst = 2;
 	atomic_set(&priv->bh_tx, 1);
 	ktime_get_ts(&itp->last_sent);
-	atomic_add(1, &itp->awaiting_confirm);
+	atomic_inc(&itp->awaiting_confirm);
 	spin_unlock_bh(&itp->tx_lock);
 	return 1;
 

bes2600/main.c

@@ -497,6 +497,7 @@ static struct ieee80211_hw *bes2600_init_common(size_t hw_priv_data_len)
 			WLAN_LINK_ID_MAX,
 			bes2600_skb_dtor,
 			hw_priv))) {
+		destroy_workqueue(hw_priv->workqueue);
 		ieee80211_free_hw(hw);
 		return NULL;
 	}
@@ -508,6 +509,7 @@ static struct ieee80211_hw *bes2600_init_common(size_t hw_priv_data_len)
 			for (; i > 0; i--)
 				bes2600_queue_deinit(&hw_priv->tx_queue[i - 1]);
 			bes2600_queue_stats_deinit(&hw_priv->tx_queue_stats);
+			destroy_workqueue(hw_priv->workqueue);
 			ieee80211_free_hw(hw);
 			return NULL;
 		}

bes2600/scan.c

@@ -257,18 +257,21 @@ int bes2600_hw_scan(struct ieee80211_hw *hw,
 
 	bes2600_pwr_set_busy_event(hw_priv, BES_PWR_LOCK_ON_SCAN);
 
-	frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
-		req->ie_len);
-	if (!frame.skb)
-		return -ENOMEM;
-
-	if (req->ie_len)
-		skb_put_data(frame.skb, req->ie, req->ie_len);
-
 	/* will be unlocked in bes2600_scan_work() */
 	down(&hw_priv->scan.lock);
 	down(&hw_priv->conf_lock);
 
+	frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
+		req->ie_len);
+	if (!frame.skb) {
+		up(&hw_priv->conf_lock);
+		up(&hw_priv->scan.lock);
+		return -ENOMEM;
+	}
+
+	if (req->ie_len)
+		skb_put_data(frame.skb, req->ie, req->ie_len);
+
 	if (frame.skb) {
 		int ret;
 		//if (priv->if_id == 0)
@@ -286,9 +289,9 @@ int bes2600_hw_scan(struct ieee80211_hw *hw,
 		}
 #endif
 		if (ret) {
+			dev_kfree_skb(frame.skb);
 			up(&hw_priv->conf_lock);
 			up(&hw_priv->scan.lock);
-			dev_kfree_skb(frame.skb);
 			return ret;
 		}
 	}
@@ -318,10 +321,10 @@ int bes2600_hw_scan(struct ieee80211_hw *hw,
 		++hw_priv->scan.n_ssids;
 	}
 
-	up(&hw_priv->conf_lock);
-
 	if (frame.skb)
 		dev_kfree_skb(frame.skb);
+
+	up(&hw_priv->conf_lock);
 #ifdef WIFI_BT_COEXIST_EPTA_ENABLE
 	bwifi_change_current_status(hw_priv, BWIFI_STATUS_SCANNING);
 #endif
@@ -362,14 +365,18 @@ int bes2600_hw_sched_scan_start(struct ieee80211_hw *hw,
 	if (req->n_ssids > hw->wiphy->max_scan_ssids)
 		return -EINVAL;
 
-	frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
-		req->ie_len);
-	if (!frame.skb)
-		return -ENOMEM;
-
 	/* will be unlocked in bes2600_scan_work() */
 	down(&hw_priv->scan.lock);
 	down(&hw_priv->conf_lock);
+
+	frame.skb = ieee80211_probereq_get(hw, priv->vif->addr, NULL, 0,
+		req->ie_len);
+	if (!frame.skb) {
+		up(&hw_priv->conf_lock);
+		up(&hw_priv->scan.lock);
+		return -ENOMEM;
+	}
+
 	if (frame.skb) {
 		int ret;
 		if (priv->if_id == 0)
@@ -380,9 +387,9 @@ int bes2600_hw_sched_scan_start(struct ieee80211_hw *hw,
 			ret = wsm_set_probe_responder(priv, true);
 		}
 		if (ret) {
+			dev_kfree_skb(frame.skb);
 			up(&hw_priv->conf_lock);
 			up(&hw_priv->scan.lock);
-			dev_kfree_skb(frame.skb);
 			return ret;
 		}
 	}
@@ -414,10 +421,10 @@ int bes2600_hw_sched_scan_start(struct ieee80211_hw *hw,
 		}
 	}
 
-	up(&hw_priv->conf_lock);
-
 	if (frame.skb)
 		dev_kfree_skb(frame.skb);
+
+	up(&hw_priv->conf_lock);
 	queue_work(hw_priv->workqueue, &hw_priv->scan.swork);
 	wiphy_warn(hw->wiphy, "<--[SCAN] Scheduled scan request.\n");
 	return 0;