[PATCH v2] staging: rtl8723bs: Fix potential race in expire_timeout_chk

[Minu Jin]

The expire_timeout_chk function currently do lock and unlock inside the
loop before calling rtw_free_stainfo().

This can be risky as the list might be changed
when the lock is briefly released.

To fix this, move expired sta_info entries into a local free_list while
holding the lock, and then perform the actual freeing after the lock is
released.

Signed-off-by: Minu Jin <s9430939@xxxxxxxxx>
---
Changes in v2:
    - Use LIST_HEAD for init list (suggested by Dan Carpenter)
    - Replace list_for_each_safe with list_for_each_entry_safe
    - Clean up unused variable 'plist' and fix type of 'tmp' iterator.
    - Remove redundant "free free_list" comment.

 drivers/staging/rtl8723bs/core/rtw_ap.c | 27 ++++++++++++-------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_ap.c b/drivers/staging/rtl8723bs/core/rtw_ap.c
index 67197c7d4a4d..d0a26134b67d 100644
--- a/drivers/staging/rtl8723bs/core/rtw_ap.c
+++ b/drivers/staging/rtl8723bs/core/rtw_ap.c
@@ -172,45 +172,44 @@ static u8 chk_sta_is_alive(struct sta_info *psta)
 
 void expire_timeout_chk(struct adapter *padapter)
 {
-	struct list_head *phead, *plist, *tmp;
+	struct list_head *phead;
 	u8 updated = false;
-	struct sta_info *psta = NULL;
+	struct sta_info *psta = NULL, *tmp;
 	struct sta_priv *pstapriv = &padapter->stapriv;
 	u8 chk_alive_num = 0;
 	char chk_alive_list[NUM_STA];
 	int i;
 
+	LIST_HEAD(free_list);
+
 	spin_lock_bh(&pstapriv->auth_list_lock);
 
 	phead = &pstapriv->auth_list;
 	/* check auth_queue */
-	list_for_each_safe(plist, tmp, phead) {
-		psta = list_entry(plist, struct sta_info, auth_list);
-
+	list_for_each_entry_safe(psta, tmp, phead, auth_list) {
 		if (psta->expire_to > 0) {
 			psta->expire_to--;
 			if (psta->expire_to == 0) {
-				list_del_init(&psta->auth_list);
+				list_move(&psta->auth_list, &free_list);
 				pstapriv->auth_list_cnt--;
-
-				spin_unlock_bh(&pstapriv->auth_list_lock);
-
-				rtw_free_stainfo(padapter, psta);
-
-				spin_lock_bh(&pstapriv->auth_list_lock);
 			}
 		}
 	}
 
 	spin_unlock_bh(&pstapriv->auth_list_lock);
+
+	list_for_each_entry_safe(psta, tmp, &free_list, auth_list) {
+		list_del_init(&psta->auth_list);
+		rtw_free_stainfo(padapter, psta);
+	}
+
 	psta = NULL;
 
 	spin_lock_bh(&pstapriv->asoc_list_lock);
 
 	phead = &pstapriv->asoc_list;
 	/* check asoc_queue */
-	list_for_each_safe(plist, tmp, phead) {
-		psta = list_entry(plist, struct sta_info, asoc_list);
+	list_for_each_entry_safe(psta, tmp, phead, asoc_list) {
 		if (chk_sta_is_alive(psta) || !psta->expire_to) {
 			psta->expire_to = pstapriv->expire_to;
 			psta->keep_alive_trycnt = 0;
-- 
2.43.0