[PATCH v1] staging: rtl8723bs: rtw_mlme: add bounds checks before ie_length subtraction

[Salman Alghamdi <me@cipherat.com>]

Add guards to ensure ie_length is large enough before subtracting
fixed IE offsets to prevent unsigned integer underflow.

Fixes: 2038fe84b8bd ("staging: rtl8723bs: fix spacing around operators")
Fixes: d3fcee1b78a5 ("staging: rtl8723bs: fix camel case in struct wlan_bssid_ex")
Closes: https://lore.kernel.org/linux-staging/DI2H39EAAFBZ.3KI5NWN02AQ2S@linux.dev/
Cc: stable@vger.kernel.org
Signed-off-by: Salman Alghamdi <me@cipherat.com>
---
 drivers/staging/rtl8723bs/core/rtw_mlme.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/rtl8723bs/core/rtw_mlme.c b/drivers/staging/rtl8723bs/core/rtw_mlme.c
index 268f294528e6..9f21a2226dbd 100644
--- a/drivers/staging/rtl8723bs/core/rtw_mlme.c
+++ b/drivers/staging/rtl8723bs/core/rtw_mlme.c
@@ -604,6 +604,8 @@ static bool rtw_is_desired_network(struct adapter *adapter, struct wlan_network
 	privacy = pnetwork->network.privacy;
 
 	if (check_fwstate(pmlmepriv, WIFI_UNDER_WPS)) {
+		if (pnetwork->network.ie_length < _FIXED_IE_LENGTH_)
+			return false;
 		if (rtw_get_wps_ie(pnetwork->network.ies + _FIXED_IE_LENGTH_, pnetwork->network.ie_length - _FIXED_IE_LENGTH_, NULL, &wps_ielen))
 			return true;
 		else
@@ -617,11 +619,15 @@ static bool rtw_is_desired_network(struct adapter *adapter, struct wlan_network
 			bselected = false;
 
 		if (psecuritypriv->ndisauthtype == Ndis802_11AuthModeWPA2PSK) {
-			p = rtw_get_ie(pnetwork->network.ies + _BEACON_IE_OFFSET_, WLAN_EID_RSN, &ie_len, (pnetwork->network.ie_length - _BEACON_IE_OFFSET_));
-			if (p && ie_len > 0)
-				bselected = true;
-			else
+			if (pnetwork->network.ie_length < _BEACON_IE_OFFSET_) {
 				bselected = false;
+			} else {
+				p = rtw_get_ie(pnetwork->network.ies + _BEACON_IE_OFFSET_, WLAN_EID_RSN, &ie_len, (pnetwork->network.ie_length - _BEACON_IE_OFFSET_));
+				if (p && ie_len > 0)
+					bselected = true;
+				else
+					bselected = false;
+			}
 		}
 	}
 
-- 
2.54.0