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/bes2600_sdio.c

@@ -29,7 +29,6 @@
 #include <linux/of_gpio.h>
 
 #include "bes2600.h"
-#include "bh.h"
 #include "sbus.h"
 #include "bes2600_plat.h"
 #include "bes2600_factory.h"
@@ -813,23 +812,10 @@ static int bes2600_sdio_extract_packets(struct sbus_priv *self, u32 ctrl_reg, u8
 		skb_put(skb, packet_len);
 		memcpy(skb->data, &data[pos], packet_len);
 		bes_devel("%s, %d,%d\n", __func__, packet_len, pos);
+		spin_lock(&self->rx_queue_lock);
+		skb_queue_tail(&self->rx_queue, skb);
 		self->rx_data_cnt++;
-		/*
+		spin_unlock(&self->rx_queue_lock);
-		 * Patch C: deliver SKB directly into the WSM/mac80211 stack
-		 * instead of skb_queue_tail-ing onto self->rx_queue for later
-		 * pickup by the bh thread.  Removes two spinlock acquires
-		 * (rx_queue->lock at queue-tail + at dequeue) per RX frame
-		 * and one bh wait-queue wake-up per IRQ batch.
-		 *
-		 * bes2600_bh_handle_rx_skb owns the SKB on every path.
-		 * Contract: process context, sleepable, caller holds no
-		 * bes2600 spinlock.  See bh.c for the contract block.
-		 *
-		 * Pre-condition satisfied here: bes2600_sdio_unlock(self)
-		 * was called at the bottom of the SDIO read sequence in
-		 * sdio_rx_work, so we hold no bes2600 mutex either.
-		 */
-		bes2600_bh_handle_rx_skb(self->core, skb);
 		packet_len = (packet_len + 3) & (~0x3);
 		pos += packet_len;
 		#ifdef BES_SDIO_OPTIMIZED_LEN
@@ -912,17 +898,12 @@ static void sdio_rx_work(struct work_struct *work)
 
 		ctrl_reg = 0;
 
-		/*
+		if (likely(self->irq_handler)) {
-		 * Patch C: with direct delivery in extract_packets, the bh
+			self->irq_handler(self->irq_priv);
-		 * thread no longer drives RX consumption — there is no
+		} else {
-		 * rx_queue to drain.  Calling self->irq_handler() here would
+			bes_err("%s,%d\n", __func__, __LINE__);
-		 * wake the bh thread for nothing on every IRQ batch.  TX
+			goto failed;
-		 * wakes still flow through bes2600_bh_wakeup() from TX
+		}
-		 * submitters and from bes2600_bh_handle_rx_skb when a
-		 * confirm releases a TX buffer; early-boot IRQs (before
-		 * fw_started) still go through self->irq_handler from the
-		 * GPIO IRQ handler's fallback branch.
-		 */
 
 	} while (again);
 

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)
@@ -958,115 +958,6 @@ static void bes2600_bh_parse_wakeup_event(struct bes2600_common *hw_priv, struct
 	}
 }
 
-/*
- * Direct-deliver an RX SKB into the WSM/mac80211 stack.
- *
- * Patch C (sdio_rx_work direct delivery): this function does the
- * per-SKB bookkeeping (sequence-number check, exception handling,
- * tx-confirm accounting, mac80211 hand-off via wsm_handle_rx) that
- * previously ran inside bes2600_bh_rx_helper after pipe_read dequeued
- * an SKB from sbus_priv->rx_queue.  It is now called inline from
- * bes2600_sdio_extract_packets, eliminating the queue + bh-wakeup
- * relay (one wait-queue wake-up + two rx_queue->lock acquires per
- * RX frame).
- *
- * Contract:
- *   - process context, sleepable.  wsm_handle_rx (wsm.c:2211, exported
- *     at wsm.c:2463) acquires wsm_cmd.lock, may call into mac80211
- *     and may sleep on wait_event_timeout (wsm.c:2036, 2091).
- *   - caller MUST hold no bes2600 spinlock.  Reference precedent:
- *     bes2600_bh_rx_helper (this file) called from the bh thread.
- *     The SDIO mutex is released at bes2600_sdio.c before
- *     extract_packets is called, so this is satisfied.
- *   - SKB ownership: function frees on every path (success and error).
- *   - Returns 0 on success, negative on error.  When the SKB carries
- *     a confirm that releases a TX buffer, the function asynchronously
- *     wakes the bh thread to drain TX (matches the in-bh tx=1
- *     signaling that bh_rx_helper used).
- */
-int bes2600_bh_handle_rx_skb(struct bes2600_common *priv, struct sk_buff *skb)
-{
-	struct wsm_hdr *wsm;
-	size_t wsm_len;
-	u16 wsm_id;
-	u8 wsm_seq;
-	int tx = 0;
-	u32 confirm_label = 0x0;
-
-	if (!skb)
-		return 0;
-
-	wsm = (struct wsm_hdr *)skb->data;
-	wsm_len = __le16_to_cpu(wsm->len);
-	if (WARN_ON(wsm_len > skb->len)) {
-		bes_err("wsm_len err %d %d\n", (int)wsm_len, (int)skb->len);
-		dev_kfree_skb(skb);
-		return -1;
-	}
-
-	if (priv->wsm_enable_wsm_dumps)
-		print_hex_dump(KERN_DEBUG, "<-- ", DUMP_PREFIX_NONE, 16, 1,
-			       skb->data, wsm_len, false);
-
-	wsm_id  = __le16_to_cpu(wsm->id) & 0xFFF;
-	wsm_seq = (__le16_to_cpu(wsm->id) >> 13) & 7;
-	bes_devel("bes2600_bh_handle_rx_skb wsm_id:0x%04x seq:%d\n",
-		  wsm_id, wsm_seq);
-
-	skb_trim(skb, wsm_len);
-
-	if (wsm_id == 0x0800) {
-		wsm_handle_exception(priv,
-				     &skb->data[sizeof(*wsm)],
-				     wsm_len - sizeof(*wsm));
-		bes_err("wsm exception\n");
-		dev_kfree_skb(skb);
-		return -1;
-	} else if ((wsm_seq != priv->wsm_rx_seq[WSM_TXRX_SEQ_IDX(wsm_id)])) {
-		bes_err("seq error! %u. %u. 0x%x.", wsm_seq,
-			priv->wsm_rx_seq[WSM_TXRX_SEQ_IDX(wsm_id)], wsm_id);
-		dev_kfree_skb(skb);
-		return -1;
-	}
-
-	bes2600_bh_parse_wakeup_event(priv, skb);
-
-	priv->wsm_rx_seq[WSM_TXRX_SEQ_IDX(wsm_id)] = (wsm_seq + 1) & 7;
-
-	if (IS_DRIVER_TO_MCU_CMD(wsm_id))
-		confirm_label = __le32_to_cpu(((struct wsm_mcu_hdr *)wsm)->handle_label);
-
-	if (WSM_CONFIRM_CONDITION(wsm_id, confirm_label)) {
-		int rc = wsm_release_tx_buffer(priv, 1);
-		bes2600_bh_dec_pending_count(priv, WSM_TXRX_SEQ_IDX(wsm->id));
-
-		if (rc < 0) {
-			bes_err("wsm_release_tx_buffer failed: %d\n", rc);
-			dev_kfree_skb(skb);
-			return rc;
-		} else if (rc > 0) {
-			tx = 1;
-		}
-	}
-
-	/* wsm_handle_rx takes care of SKB lifetime: zeroes *skb_p if consumed. */
-	if (wsm_handle_rx(priv, wsm_id, wsm, &skb)) {
-		bes_err("wsm_handle_rx failed (id=0x%04x)\n", wsm_id);
-		if (skb)
-			dev_kfree_skb(skb);
-		return -1;
-	}
-
-	if (skb)
-		dev_kfree_skb(skb);
-
-	if (tx)
-		bes2600_bh_wakeup(priv);
-
-	return 0;
-}
-EXPORT_SYMBOL(bes2600_bh_handle_rx_skb);
-
 static int bes2600_bh_rx_helper(struct bes2600_common *priv, int *tx)
 {
 	struct sk_buff *skb = NULL;
@@ -1243,7 +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);
@@ -1544,7 +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/bh.h

@@ -36,13 +36,6 @@ void bes2600_enable_powersave(struct bes2600_vif *priv,
 int wsm_release_tx_buffer(struct bes2600_common *hw_priv, int count);
 int wsm_release_vif_tx_buffer(struct bes2600_common *hw_priv, int if_id,
 				int count);
-/*
- * Direct-deliver an RX SKB into the WSM/mac80211 stack.
- * Process context, sleepable, caller holds no bes2600 spinlock.
- * Function frees skb on every path. See bh.c for full contract.
- */
-int bes2600_bh_handle_rx_skb(struct bes2600_common *hw_priv,
-			     struct sk_buff *skb);
 int bes2600_bh_sw_process(struct bes2600_common *hw_priv,
 			 struct wsm_tx_confirm *tx_confirm);
 

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;