staging: rtl8723bs: properly validate the data in rtw_get_ie_ex()

Just like in commit 154828b ("staging: rtl8723bs: fix out-of-bounds
read in rtw_get_ie() parser"), we don't trust the data in the frame so
we should check the length better before acting on it

Cc: stable <stable@kernel.org>
Assisted-by: gkh_clanker_2000
Tested-by: Navaneeth K <knavaneeth786@gmail.com>
Reviewed-by: Navaneeth K <knavaneeth786@gmail.com>
Link: https://patch.msgid.link/2026022336-arrange-footwork-6e54@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gregkh

drivers/staging/rtl8723bs/core/rtw_ieee80211.c

@@ -186,20 +186,25 @@ u8 *rtw_get_ie_ex(u8 *in_ie, uint in_len, u8 eid, u8 *oui, u8 oui_len, u8 *ie, u
 
 	cnt = 0;
 
-	while (cnt < in_len) {
+	while (cnt + 2 <= in_len) {
+		u8 ie_len = in_ie[cnt + 1];
+
+		if (cnt + 2 + ie_len > in_len)
+			break;
+
 		if (eid == in_ie[cnt]
-			&& (!oui || !memcmp(&in_ie[cnt+2], oui, oui_len))) {
+			&& (!oui || (ie_len >= oui_len && !memcmp(&in_ie[cnt + 2], oui, oui_len)))) {
 			target_ie = &in_ie[cnt];
 
 			if (ie)
-				memcpy(ie, &in_ie[cnt], in_ie[cnt+1]+2);
+				memcpy(ie, &in_ie[cnt], ie_len + 2);
 
 			if (ielen)
-				*ielen = in_ie[cnt+1]+2;
+				*ielen = ie_len + 2;
 
 			break;
 		}
-		cnt += in_ie[cnt+1]+2; /* goto next */
+		cnt += ie_len + 2; /* goto next */
 	}
 
 	return target_ie;