brcmfmac: avoid potential stack overflow in brcmf_cfg80211_start_ap()

User-space can choose to omit NL80211_ATTR_SSID and only provide raw
IE TLV data. When doing so it can provide SSID IE with length exceeding
the allowed size. The driver further processes this IE copying it
into a local variable without checking the length. Hence stack can be
corrupted and used as exploit.

Cc: stable@vger.kernel.org # v4.7
Reported-by: Daxing Guo <freener.gdx@gmail.com>
Reviewed-by: Hante Meuleman <hante.meuleman@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Reviewed-by: Franky Lin <franky.lin@broadcom.com>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
static int brcmf_convert_nl80211_tdls_oper(enum nl80211_tdls_operation oper)
{
	int ret;

	switch (oper) {
	case NL80211_TDLS_DISCOVERY_REQ:
		ret = BRCMF_TDLS_MANUAL_EP_DISCOVERY;
		break;
	case NL80211_TDLS_SETUP:
		ret = BRCMF_TDLS_MANUAL_EP_CREATE;
		break;
	case NL80211_TDLS_TEARDOWN:
		ret = BRCMF_TDLS_MANUAL_EP_DELETE;
		break;
	default:
		brcmf_err("unsupported operation: %d\n", oper);
		ret = -EOPNOTSUPP;
	}
	return ret;
}

static int brcmf_convert_nl80211_tdls_oper(enum nl80211_tdls_operation oper)
{
	int ret;

	switch (oper) {
	case NL80211_TDLS_DISCOVERY_REQ:
		ret = BRCMF_TDLS_MANUAL_EP_DISCOVERY;
		break;
	case NL80211_TDLS_SETUP:
		ret = BRCMF_TDLS_MANUAL_EP_CREATE;
		break;
	case NL80211_TDLS_TEARDOWN:
		ret = BRCMF_TDLS_MANUAL_EP_DELETE;
		break;
	default:
		brcmf_err("unsupported operation: %d\n", oper);
		ret = -EOPNOTSUPP;
	}
	return ret;
}
