[PATCH 4/4] staging: rtl8723bs: fix NULL deref on bcmc station lookup in defrag path

[Yi Cong]

From: Yi Cong <yicong@xxxxxxxxxx>

In recvframe_chk_defrag(), when a fragment's transmitter address is unknown
(no associated station) and the frame is not a data frame, the code looks
up the broadcast/multicast station with rtw_get_bcmc_stainfo() and
immediately dereferences the result to obtain defrag_q, without a NULL
check. rtw_get_bcmc_stainfo() (a thin wrapper around rtw_get_stainfo())
can return NULL, for example if the bcmc station has not been or is no
longer allocated.

Every other call site of rtw_get_bcmc_stainfo() in the driver checks the
return value; this one was missed. A fragment with an unknown transmitter
address received from the network (e.g. an injected/rogue management
fragment) could thus trigger a NULL pointer dereference panic.

Check the return value and set pdefrag_q = NULL when no bcmc station is
available, consistent with the adjacent data-frame branch (the later code
already handles pdefrag_q == NULL).

Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Signed-off-by: Yi Cong <yicong@xxxxxxxxxx>
---
 drivers/staging/rtl8723bs/core/rtw_recv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 86c5e2c4e7dd..ffcee431caf5 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -1146,7 +1146,10 @@ static union recv_frame *recvframe_chk_defrag(struct adapter *padapter, union re
 
 		if (type != WIFI_DATA_TYPE) {
 			psta = rtw_get_bcmc_stainfo(padapter);
-			pdefrag_q = &psta->sta_recvpriv.defrag_q;
+			if (psta)
+				pdefrag_q = &psta->sta_recvpriv.defrag_q;
+			else
+				pdefrag_q = NULL;
 		} else {
 			pdefrag_q = NULL;
 		}
-- 
2.25.1