Staging: rtl8723bs: prevent buffer overflow in update_sta_support_rate()

The "ie_len" variable is in the 0-255 range and it comes from the
network. If it's over NDIS_802_11_LENGTH_RATES_EX (16) then that will
lead to memory corruption.

Fixes: 554c0a3abf21 ("staging: Add rtl8723bs sdio wifi driver")
Signed-off-by: Dan Carpenter <[e-mail]>
Cc: stable <[e-mail]>
Link: https://lore.kernel.org/r/20200603101958.GA1845750@mwanda
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/rtl8723bs/core/rtw_wlan_util.c

···
 	pIE = (struct ndis_80211_var_ie *)rtw_get_ie(pvar_ie, _SUPPORTEDRATES_IE_, &ie_len, var_ie_len);
 	if (!pIE)
 		return _FAIL;
+	if (ie_len > sizeof(pmlmeinfo->FW_sta_info[cam_idx].SupportedRates))
+		return _FAIL;
 
 	memcpy(pmlmeinfo->FW_sta_info[cam_idx].SupportedRates, pIE->data, ie_len);
 	supportRateNum = ie_len;
 
 	pIE = (struct ndis_80211_var_ie *)rtw_get_ie(pvar_ie, _EXT_SUPPORTEDRATES_IE_, &ie_len, var_ie_len);
-	if (pIE)
+	if (pIE && (ie_len <= sizeof(pmlmeinfo->FW_sta_info[cam_idx].SupportedRates) - supportRateNum))
 		memcpy((pmlmeinfo->FW_sta_info[cam_idx].SupportedRates + supportRateNum), pIE->data, ie_len);
 
 	return _SUCCESS;