cfg80211: don't get expired BSSes

When kernel-internal users use cfg80211_get_bss()
to get a reference to a BSS struct, they may end
up getting one that would have been removed from
the list if there had been any userspace access
to the list. This leads to inconsistencies and
problems.

Fix it by making cfg80211_get_bss() ignore BSSes
that cfg80211_bss_expire() would remove.

Fixes http://bugzilla.intellinuxwireless.org/show_bug.cgi?id=2180

Cc: stable@kernel.org
Reported-by: Jiajia Zheng <jiajia.zheng@intel.com>
Tested-by: Jiajia Zheng <jiajia.zheng@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/scan.c

@@ -275,6 +275,7 @@ struct cfg80211_bss *cfg80211_get_bss(struct wiphy *wiphy,
 {
 	struct cfg80211_registered_device *dev = wiphy_to_dev(wiphy);
 	struct cfg80211_internal_bss *bss, *res = NULL;
+	unsigned long now = jiffies;
 
 	spin_lock_bh(&dev->bss_lock);
 
@@ -283,6 +284,10 @@ struct cfg80211_bss *cfg80211_get_bss(struct wiphy *wiphy,
 			continue;
 		if (channel && bss->pub.channel != channel)
 			continue;
+		/* Don't get expired BSS structs */
+		if (time_after(now, bss->ts + IEEE80211_SCAN_RESULT_EXPIRE) &&
+		    !atomic_read(&bss->hold))
+			continue;
 		if (is_bss(&bss->pub, bssid, ssid, ssid_len)) {
 			res = bss;
 			kref_get(&res->ref);