staging: wfx: fix RCU usage between hif_join() and ieee80211_bss_get_ie()

Access to result of ieee80211_bss_get_ie() is protected by RCU. In other
hand, function hif_join() can sleep and cannot be called with RCU
locked.

Provide a copy of "ssidie" to hif_join() to solve this behavior.

Fixes: 9ced9b5937 ("staging: wfx: simplify hif_join()")
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200310101356.182818-6-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_tx.c

@@ -290,7 +290,7 @@ int hif_stop_scan(struct wfx_vif *wvif)
 }
 
 int hif_join(struct wfx_vif *wvif, const struct ieee80211_bss_conf *conf,
-	     const struct ieee80211_channel *channel, const u8 *ssidie)
+	     struct ieee80211_channel *channel, const u8 *ssid, int ssidlen)
 {
 	int ret;
 	struct hif_msg *hif;
@@ -308,9 +308,9 @@ int hif_join(struct wfx_vif *wvif, const struct ieee80211_bss_conf *conf,
 	body->basic_rate_set =
 		cpu_to_le32(wfx_rate_mask_to_hw(wvif->wdev, conf->basic_rates));
 	memcpy(body->bssid, conf->bssid, sizeof(body->bssid));
-	if (!conf->ibss_joined && ssidie) {
-		body->ssid_length = cpu_to_le32(ssidie[1]);
-		memcpy(body->ssid, &ssidie[2], ssidie[1]);
+	if (!conf->ibss_joined && ssid) {
+		body->ssid_length = cpu_to_le32(ssidlen);
+		memcpy(body->ssid, ssid, ssidlen);
 	}
 	wfx_fill_header(hif, wvif->id, HIF_REQ_ID_JOIN, sizeof(*body));
 	ret = wfx_cmd_send(wvif->wdev, hif, NULL, 0, false);

drivers/staging/wfx/hif_tx.h

@@ -46,7 +46,7 @@ int hif_scan(struct wfx_vif *wvif, struct cfg80211_scan_request *req80211,
 	     int chan_start, int chan_num);
 int hif_stop_scan(struct wfx_vif *wvif);
 int hif_join(struct wfx_vif *wvif, const struct ieee80211_bss_conf *conf,
-	     const struct ieee80211_channel *channel, const u8 *ssidie);
+	     struct ieee80211_channel *channel, const u8 *ssid, int ssidlen);
 int hif_set_pm(struct wfx_vif *wvif, bool ps, int dynamic_ps_timeout);
 int hif_set_bss_params(struct wfx_vif *wvif,
 		       const struct hif_req_set_bss_params *arg);

drivers/staging/wfx/sta.c

@@ -491,9 +491,11 @@ static void wfx_set_mfp(struct wfx_vif *wvif,
 static void wfx_do_join(struct wfx_vif *wvif)
 {
 	int ret;
-	const u8 *ssidie;
 	struct ieee80211_bss_conf *conf = &wvif->vif->bss_conf;
 	struct cfg80211_bss *bss = NULL;
+	u8 ssid[IEEE80211_MAX_SSID_LEN];
+	const u8 *ssidie = NULL;
+	int ssidlen = 0;
 
 	wfx_tx_lock_flush(wvif->wdev);
 
@@ -514,11 +516,14 @@ static void wfx_do_join(struct wfx_vif *wvif)
 	if (!wvif->beacon_int)
 		wvif->beacon_int = 1;
 
-	rcu_read_lock();
+	rcu_read_lock(); // protect ssidie
 	if (!conf->ibss_joined)
 		ssidie = ieee80211_bss_get_ie(bss, WLAN_EID_SSID);
-	else
-		ssidie = NULL;
+	if (ssidie) {
+		ssidlen = ssidie[1];
+		memcpy(ssid, &ssidie[2], ssidie[1]);
+	}
+	rcu_read_unlock();
 
 	wfx_tx_flush(wvif->wdev);
 
@@ -527,10 +532,8 @@ static void wfx_do_join(struct wfx_vif *wvif)
 
 	wfx_set_mfp(wvif, bss);
 
-	/* Perform actual join */
 	wvif->wdev->tx_burst_idx = -1;
-	ret = hif_join(wvif, conf, wvif->channel, ssidie);
-	rcu_read_unlock();
+	ret = hif_join(wvif, conf, wvif->channel, ssid, ssidlen);
 	if (ret) {
 		ieee80211_connection_loss(wvif->vif);
 		wvif->join_complete_status = -1;