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_setup_wiphybands(struct wiphy *wiphy)
{
	struct brcmf_cfg80211_info *cfg = wiphy_priv(wiphy);
	struct brcmf_if *ifp = netdev_priv(cfg_to_ndev(cfg));
	u32 nmode = 0;
	u32 vhtmode = 0;
	u32 bw_cap[2] = { WLC_BW_20MHZ_BIT, WLC_BW_20MHZ_BIT };
	u32 rxchain;
	u32 nchain;
	int err;
	s32 i;
	struct ieee80211_supported_band *band;
	u32 txstreams = 0;
	u32 txbf_bfe_cap = 0;
	u32 txbf_bfr_cap = 0;

	(void)brcmf_fil_iovar_int_get(ifp, "vhtmode", &vhtmode);
	err = brcmf_fil_iovar_int_get(ifp, "nmode", &nmode);
	if (err) {
		brcmf_err("nmode error (%d)\n", err);
	} else {
		brcmf_get_bwcap(ifp, bw_cap);
	}
	brcmf_dbg(INFO, "nmode=%d, vhtmode=%d, bw_cap=(%d, %d)\n",
		  nmode, vhtmode, bw_cap[NL80211_BAND_2GHZ],
		  bw_cap[NL80211_BAND_5GHZ]);

	err = brcmf_fil_iovar_int_get(ifp, "rxchain", &rxchain);
	if (err) {
		brcmf_err("rxchain error (%d)\n", err);
		nchain = 1;
	} else {
		for (nchain = 0; rxchain; nchain++)
			rxchain = rxchain & (rxchain - 1);
	}
	brcmf_dbg(INFO, "nchain=%d\n", nchain);

	err = brcmf_construct_chaninfo(cfg, bw_cap);
	if (err) {
		brcmf_err("brcmf_construct_chaninfo failed (%d)\n", err);
		return err;
	}

	if (vhtmode) {
		(void)brcmf_fil_iovar_int_get(ifp, "txstreams", &txstreams);
		(void)brcmf_fil_iovar_int_get(ifp, "txbf_bfe_cap",
					      &txbf_bfe_cap);
		(void)brcmf_fil_iovar_int_get(ifp, "txbf_bfr_cap",
					      &txbf_bfr_cap);
	}

	wiphy = cfg_to_wiphy(cfg);
	for (i = 0; i < ARRAY_SIZE(wiphy->bands); i++) {
		band = wiphy->bands[i];
		if (band == NULL)
			continue;

		if (nmode)
			brcmf_update_ht_cap(band, bw_cap, nchain);
		if (vhtmode)
			brcmf_update_vht_cap(band, bw_cap, nchain, txstreams,
					     txbf_bfe_cap, txbf_bfr_cap);
	}

	return 0;
}

static int brcmf_setup_wiphybands(struct wiphy *wiphy)
{
	struct brcmf_cfg80211_info *cfg = wiphy_priv(wiphy);
	struct brcmf_if *ifp = netdev_priv(cfg_to_ndev(cfg));
	u32 nmode = 0;
	u32 vhtmode = 0;
	u32 bw_cap[2] = { WLC_BW_20MHZ_BIT, WLC_BW_20MHZ_BIT };
	u32 rxchain;
	u32 nchain;
	int err;
	s32 i;
	struct ieee80211_supported_band *band;
	u32 txstreams = 0;
	u32 txbf_bfe_cap = 0;
	u32 txbf_bfr_cap = 0;

	(void)brcmf_fil_iovar_int_get(ifp, "vhtmode", &vhtmode);
	err = brcmf_fil_iovar_int_get(ifp, "nmode", &nmode);
	if (err) {
		brcmf_err("nmode error (%d)\n", err);
	} else {
		brcmf_get_bwcap(ifp, bw_cap);
	}
	brcmf_dbg(INFO, "nmode=%d, vhtmode=%d, bw_cap=(%d, %d)\n",
		  nmode, vhtmode, bw_cap[NL80211_BAND_2GHZ],
		  bw_cap[NL80211_BAND_5GHZ]);

	err = brcmf_fil_iovar_int_get(ifp, "rxchain", &rxchain);
	if (err) {
		brcmf_err("rxchain error (%d)\n", err);
		nchain = 1;
	} else {
		for (nchain = 0; rxchain; nchain++)
			rxchain = rxchain & (rxchain - 1);
	}
	brcmf_dbg(INFO, "nchain=%d\n", nchain);

	err = brcmf_construct_chaninfo(cfg, bw_cap);
	if (err) {
		brcmf_err("brcmf_construct_chaninfo failed (%d)\n", err);
		return err;
	}

	if (vhtmode) {
		(void)brcmf_fil_iovar_int_get(ifp, "txstreams", &txstreams);
		(void)brcmf_fil_iovar_int_get(ifp, "txbf_bfe_cap",
					      &txbf_bfe_cap);
		(void)brcmf_fil_iovar_int_get(ifp, "txbf_bfr_cap",
					      &txbf_bfr_cap);
	}

	wiphy = cfg_to_wiphy(cfg);
	for (i = 0; i < ARRAY_SIZE(wiphy->bands); i++) {
		band = wiphy->bands[i];
		if (band == NULL)
			continue;

		if (nmode)
			brcmf_update_ht_cap(band, bw_cap, nchain);
		if (vhtmode)
			brcmf_update_vht_cap(band, bw_cap, nchain, txstreams,
					     txbf_bfe_cap, txbf_bfr_cap);
	}

	return 0;
}
