[RFC PATCH] 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>
---
Hi,

I noticed this lock-unlock pattern in expire_timeout_chk() while
studying the code and it looked like a potential race condition.

I've refactored the code to use a local list so we can handle the
cleanup after releasing the lock. What do you think about this approach?

Any feedback is appreciated.

 drivers/staging/rtl8723bs/core/rtw_ap.c | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_ap.c b/drivers/staging/rtl8723bs/core/rtw_ap.c
index 67197c7d4a4d..5947f6363ab0 100644
--- a/drivers/staging/rtl8723bs/core/rtw_ap.c
+++ b/drivers/staging/rtl8723bs/core/rtw_ap.c
@@ -179,6 +179,9 @@ void expire_timeout_chk(struct adapter *padapter)
 	u8 chk_alive_num = 0;
 	char chk_alive_list[NUM_STA];
 	int i;
+	struct list_head free_list;
+
+	INIT_LIST_HEAD(&free_list);
 
 	spin_lock_bh(&pstapriv->auth_list_lock);
 
@@ -190,19 +193,21 @@ void expire_timeout_chk(struct adapter *padapter)
 		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);
+
+	/* free free_list */
+	list_for_each_safe(plist, tmp, &free_list) {
+		psta = list_entry(plist, struct sta_info, auth_list);
+		list_del_init(&psta->auth_list);
+		rtw_free_stainfo(padapter, psta);
+	}
+
 	psta = NULL;
 
 	spin_lock_bh(&pstapriv->asoc_list_lock);
-- 
2.43.0