[PATCH] nl80211: take RCU read lock when calling ieee80211_bss_get_ie()

[Dominik Brodowski]

As ieee80211_bss_get_ie() derefences an RCU, it needs to be called with
rcu_read_lock held.

Fixes: 44905265bc15 ("nl80211: don't expose wdev->ssid for most interfaces")
Signed-off-by: Dominik Brodowski <li...@dominikbrodowski.net>
---

This patch fixes the regression I reported in the last couple of weeks for
various v4.15-rcX revisions to netdev, where a "suspicious RCU usage"
showed up in net/wireless/util.c:778.

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 2b3dbcd40e46..1eecc249fb5e 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -2618,8 +2618,10 @@ static int nl80211_send_iface(struct sk_buff *msg, u32 
portid, u32 seq, int flag
                const u8 *ssid_ie;
                if (!wdev->current_bss)
                        break;
+               rcu_read_lock();
                ssid_ie = ieee80211_bss_get_ie(&wdev->current_bss->pub,
                                               WLAN_EID_SSID);
+               rcu_read_unlock();
                if (!ssid_ie)
                        break;
                if (nla_put(msg, NL80211_ATTR_SSID, ssid_ie[1], ssid_ie + 2))