staging: rtl8188eu: fix potential memory corruption in rtw_check_beacon_data()

The "ie_len" is a value in the 1-255 range that comes from the user.  We
have to cap it to ensure that it's not too large or it could lead to
memory corruption.

Fixes: 9a7fe54 ("staging: r8188eu: Add source files for new driver - part 1")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/YEHyQCrFZKTXyT7J@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Dan Carpenter

drivers/staging/rtl8188eu/core/rtw_ap.c

@@ -791,6 +791,7 @@ int rtw_check_beacon_data(struct adapter *padapter, u8 *pbuf,  int len)
 	p = rtw_get_ie(ie + _BEACON_IE_OFFSET_, WLAN_EID_SSID, &ie_len,
 		       pbss_network->ie_length - _BEACON_IE_OFFSET_);
 	if (p && ie_len > 0) {
+		ie_len = min_t(int, ie_len, sizeof(pbss_network->ssid.ssid));
 		memset(&pbss_network->ssid, 0, sizeof(struct ndis_802_11_ssid));
 		memcpy(pbss_network->ssid.ssid, p + 2, ie_len);
 		pbss_network->ssid.ssid_length = ie_len;
@@ -811,6 +812,7 @@ int rtw_check_beacon_data(struct adapter *padapter, u8 *pbuf,  int len)
 	p = rtw_get_ie(ie + _BEACON_IE_OFFSET_, WLAN_EID_SUPP_RATES, &ie_len,
 		       pbss_network->ie_length - _BEACON_IE_OFFSET_);
 	if (p) {
+		ie_len = min_t(int, ie_len, NDIS_802_11_LENGTH_RATES_EX);
 		memcpy(supportRate, p + 2, ie_len);
 		supportRateNum = ie_len;
 	}
@@ -819,6 +821,8 @@ int rtw_check_beacon_data(struct adapter *padapter, u8 *pbuf,  int len)
 	p = rtw_get_ie(ie + _BEACON_IE_OFFSET_, WLAN_EID_EXT_SUPP_RATES,
 		       &ie_len, pbss_network->ie_length - _BEACON_IE_OFFSET_);
 	if (p) {
+		ie_len = min_t(int, ie_len,
+			       NDIS_802_11_LENGTH_RATES_EX - supportRateNum);
 		memcpy(supportRate + supportRateNum, p + 2, ie_len);
 		supportRateNum += ie_len;
 	}
@@ -934,6 +938,7 @@ int rtw_check_beacon_data(struct adapter *padapter, u8 *pbuf,  int len)
 
 		pht_cap->mcs.rx_mask[0] = 0xff;
 		pht_cap->mcs.rx_mask[1] = 0x0;
+		ie_len = min_t(int, ie_len, sizeof(pmlmepriv->htpriv.ht_cap));
 		memcpy(&pmlmepriv->htpriv.ht_cap, p + 2, ie_len);
 	}