[PATCH] mt76: hold RCU lock when calling ieee80211_find_sta_by_ifaddr()

[Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>]

ieee80211_find_sta_by_ifaddr() must be called under the RCU lock and
the resulting pointer is only valid under RCU lock as well.

Fix mt76_check_sta() to hold RCU read lock before it calls
ieee80211_find_sta_by_ifaddr() and release it when the resulting
pointer is no longer needed.

This problem was found while reviewing code to debug RCU warn from
ath10k_wmi_tlv_parse_peer_stats_info() and a subsequent manual audit
of other callers of ieee80211_find_sta_by_ifaddr() that don't hold
RCU read lock.

Signed-off-by: Shuah Khan <skhan@xxxxxxxxxxxxxxxxxxx>
---
- Note: This patch is compile tested. I don't have access to
  hardware.

 drivers/net/wireless/mediatek/mt76/mac80211.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/mediatek/mt76/mac80211.c b/drivers/net/wireless/mediatek/mt76/mac80211.c
index a840396f2c74..3c732da2a53f 100644
--- a/drivers/net/wireless/mediatek/mt76/mac80211.c
+++ b/drivers/net/wireless/mediatek/mt76/mac80211.c
@@ -867,6 +867,9 @@ mt76_check_sta(struct mt76_dev *dev, struct sk_buff *skb)
 	bool ps;
 
 	hw = mt76_phy_hw(dev, status->ext_phy);
+
+	rcu_read_lock();
+
 	if (ieee80211_is_pspoll(hdr->frame_control) && !wcid) {
 		sta = ieee80211_find_sta_by_ifaddr(hw, hdr->addr2, NULL);
 		if (sta)
@@ -876,7 +879,7 @@ mt76_check_sta(struct mt76_dev *dev, struct sk_buff *skb)
 	mt76_airtime_check(dev, skb);
 
 	if (!wcid || !wcid->sta)
-		return;
+		goto exit;
 
 	sta = container_of((void *)wcid, struct ieee80211_sta, drv_priv);
 
@@ -886,17 +889,17 @@ mt76_check_sta(struct mt76_dev *dev, struct sk_buff *skb)
 	wcid->inactive_count = 0;
 
 	if (!test_bit(MT_WCID_FLAG_CHECK_PS, &wcid->flags))
-		return;
+		goto exit;
 
 	if (ieee80211_is_pspoll(hdr->frame_control)) {
 		ieee80211_sta_pspoll(sta);
-		return;
+		goto exit;
 	}
 
 	if (ieee80211_has_morefrags(hdr->frame_control) ||
 	    !(ieee80211_is_mgmt(hdr->frame_control) ||
 	      ieee80211_is_data(hdr->frame_control)))
-		return;
+		goto exit;
 
 	ps = ieee80211_has_pm(hdr->frame_control);
 
@@ -905,7 +908,7 @@ mt76_check_sta(struct mt76_dev *dev, struct sk_buff *skb)
 		ieee80211_sta_uapsd_trigger(sta, status->tid);
 
 	if (!!test_bit(MT_WCID_FLAG_PS, &wcid->flags) == ps)
-		return;
+		goto exit;
 
 	if (ps)
 		set_bit(MT_WCID_FLAG_PS, &wcid->flags);
@@ -914,6 +917,9 @@ mt76_check_sta(struct mt76_dev *dev, struct sk_buff *skb)
 
 	dev->drv->sta_ps(dev, sta, ps);
 	ieee80211_sta_ps_transition(sta, ps);
+
+exit:
+	rcu_read_unlock();
 }
 
 void mt76_rx_complete(struct mt76_dev *dev, struct sk_buff_head *frames,
-- 
2.27.0