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 s32 brcmf_inform_single_bss(struct brcmf_cfg80211_info *cfg,
				   struct brcmf_bss_info_le *bi)
{
	struct wiphy *wiphy = cfg_to_wiphy(cfg);
	struct ieee80211_channel *notify_channel;
	struct cfg80211_bss *bss;
	struct ieee80211_supported_band *band;
	struct brcmu_chan ch;
	u16 channel;
	u32 freq;
	u16 notify_capability;
	u16 notify_interval;
	u8 *notify_ie;
	size_t notify_ielen;
	s32 notify_signal;

	if (le32_to_cpu(bi->length) > WL_BSS_INFO_MAX) {
		brcmf_err("Bss info is larger than buffer. Discarding\n");
		return 0;
	}

	if (!bi->ctl_ch) {
		ch.chspec = le16_to_cpu(bi->chanspec);
		cfg->d11inf.decchspec(&ch);
		bi->ctl_ch = ch.control_ch_num;
	}
	channel = bi->ctl_ch;

	if (channel <= CH_MAX_2G_CHANNEL)
		band = wiphy->bands[NL80211_BAND_2GHZ];
	else
		band = wiphy->bands[NL80211_BAND_5GHZ];

	freq = ieee80211_channel_to_frequency(channel, band->band);
	notify_channel = ieee80211_get_channel(wiphy, freq);

	notify_capability = le16_to_cpu(bi->capability);
	notify_interval = le16_to_cpu(bi->beacon_period);
	notify_ie = (u8 *)bi + le16_to_cpu(bi->ie_offset);
	notify_ielen = le32_to_cpu(bi->ie_length);
	notify_signal = (s16)le16_to_cpu(bi->RSSI) * 100;

	brcmf_dbg(CONN, "bssid: %pM\n", bi->BSSID);
	brcmf_dbg(CONN, "Channel: %d(%d)\n", channel, freq);
	brcmf_dbg(CONN, "Capability: %X\n", notify_capability);
	brcmf_dbg(CONN, "Beacon interval: %d\n", notify_interval);
	brcmf_dbg(CONN, "Signal: %d\n", notify_signal);

	bss = cfg80211_inform_bss(wiphy, notify_channel,
				  CFG80211_BSS_FTYPE_UNKNOWN,
				  (const u8 *)bi->BSSID,
				  0, notify_capability,
				  notify_interval, notify_ie,
				  notify_ielen, notify_signal,
				  GFP_KERNEL);

	if (!bss)
		return -ENOMEM;

	cfg80211_put_bss(wiphy, bss);

	return 0;
}

static s32 brcmf_inform_single_bss(struct brcmf_cfg80211_info *cfg,
				   struct brcmf_bss_info_le *bi)
{
	struct wiphy *wiphy = cfg_to_wiphy(cfg);
	struct ieee80211_channel *notify_channel;
	struct cfg80211_bss *bss;
	struct ieee80211_supported_band *band;
	struct brcmu_chan ch;
	u16 channel;
	u32 freq;
	u16 notify_capability;
	u16 notify_interval;
	u8 *notify_ie;
	size_t notify_ielen;
	s32 notify_signal;

	if (le32_to_cpu(bi->length) > WL_BSS_INFO_MAX) {
		brcmf_err("Bss info is larger than buffer. Discarding\n");
		return 0;
	}

	if (!bi->ctl_ch) {
		ch.chspec = le16_to_cpu(bi->chanspec);
		cfg->d11inf.decchspec(&ch);
		bi->ctl_ch = ch.control_ch_num;
	}
	channel = bi->ctl_ch;

	if (channel <= CH_MAX_2G_CHANNEL)
		band = wiphy->bands[NL80211_BAND_2GHZ];
	else
		band = wiphy->bands[NL80211_BAND_5GHZ];

	freq = ieee80211_channel_to_frequency(channel, band->band);
	notify_channel = ieee80211_get_channel(wiphy, freq);

	notify_capability = le16_to_cpu(bi->capability);
	notify_interval = le16_to_cpu(bi->beacon_period);
	notify_ie = (u8 *)bi + le16_to_cpu(bi->ie_offset);
	notify_ielen = le32_to_cpu(bi->ie_length);
	notify_signal = (s16)le16_to_cpu(bi->RSSI) * 100;

	brcmf_dbg(CONN, "bssid: %pM\n", bi->BSSID);
	brcmf_dbg(CONN, "Channel: %d(%d)\n", channel, freq);
	brcmf_dbg(CONN, "Capability: %X\n", notify_capability);
	brcmf_dbg(CONN, "Beacon interval: %d\n", notify_interval);
	brcmf_dbg(CONN, "Signal: %d\n", notify_signal);

	bss = cfg80211_inform_bss(wiphy, notify_channel,
				  CFG80211_BSS_FTYPE_UNKNOWN,
				  (const u8 *)bi->BSSID,
				  0, notify_capability,
				  notify_interval, notify_ie,
				  notify_ielen, notify_signal,
				  GFP_KERNEL);

	if (!bss)
		return -ENOMEM;

	cfg80211_put_bss(wiphy, bss);

	return 0;
}
