cfg80211: check for and abort dangling scan requests

If you trigger a scan request on an interface and then
take it down, or rmmod the module or unplug the device
the driver might "forget" to cancel the scan request.
That is a bug in the driver, but the current behaviour
is that we just hang endlessly waiting for the netdev
refcount to become 0 which it never will. To improve
robustness, check for this situation in cfg80211, warn
about it and clean up behind the driver. I don't just
clean up silently because it's likely that the driver
also has some internal state it has now leaked.

Additionally, this fixes a locking bug, clearing the
scan_req pointer should be done under the rdev lock.

Finally, we also need to _wait_ for the scan work and
not just abort it since it might be pending and wanting
to do a cleanup.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

3 files changed, 26 insertions, 11 deletions

diff --git a/net/wireless/core.c b/net/wireless/core.c
index e630648fef79..35d83bedfe5b 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -601,8 +601,8 @@ void wiphy_unregister(struct wiphy *wiphy)
 
         mutex_unlock(&cfg80211_mutex);
 
+        flush_work(&rdev->scan_done_wk);
         cancel_work_sync(&rdev->conn_work);
-        cancel_work_sync(&rdev->scan_done_wk);
         kfree(rdev->scan_req);
         flush_work(&rdev->event_work);
 }
@@ -728,6 +728,13 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 #endif
                 break;
         case NETDEV_UNREGISTER:
+                cfg80211_lock_rdev(rdev);
+
+                if (WARN_ON(rdev->scan_req && rdev->scan_req->dev == dev)) {
+                        rdev->scan_req->aborted = true;
+                        ___cfg80211_scan_done(rdev);
+                }
+
                 mutex_lock(&rdev->devlist_mtx);
                 /*
                  * It is possible to get NETDEV_UNREGISTER
@@ -746,6 +753,7 @@ static int cfg80211_netdev_notifier_call(struct notifier_block * nb,
 #endif
                 }
                 mutex_unlock(&rdev->devlist_mtx);
+                cfg80211_unlock_rdev(rdev);
                 break;
         case NETDEV_PRE_UP:
                 if (!(wdev->wiphy->interface_modes & BIT(wdev->iftype)))
diff --git a/net/wireless/core.h b/net/wireless/core.h
index f7be3a9b427e..c603f5286326 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -368,6 +368,7 @@ void cfg80211_sme_scan_done(struct net_device *dev);
 void cfg80211_sme_rx_auth(struct net_device *dev, const u8 *buf, size_t len);
 void cfg80211_sme_disassoc(struct net_device *dev, int idx);
 void __cfg80211_scan_done(struct work_struct *wk);
+void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev);
 void cfg80211_upload_connect_keys(struct wireless_dev *wdev);
 
 struct ieee80211_channel *
diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index e6c1f11595da..fe575a24c95c 100644
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -18,19 +18,14 @@
 
 #define IEEE80211_SCAN_RESULT_EXPIRE    (15 * HZ)
 
-void __cfg80211_scan_done(struct work_struct *wk)
+void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev)
 {
-        struct cfg80211_registered_device *rdev;
         struct cfg80211_scan_request *request;
         struct net_device *dev;
 #ifdef CONFIG_WIRELESS_EXT
         union iwreq_data wrqu;
 #endif
 
-        rdev = container_of(wk, struct cfg80211_registered_device,
-                            scan_done_wk);
-
-        mutex_lock(&rdev->mtx);
         request = rdev->scan_req;
 
         dev = request->dev;
@@ -43,9 +38,9 @@ void __cfg80211_scan_done(struct work_struct *wk)
         cfg80211_sme_scan_done(dev);
 
         if (request->aborted)
-                nl80211_send_scan_aborted(wiphy_to_dev(request->wiphy), dev);
+                nl80211_send_scan_aborted(rdev, dev);
         else
-                nl80211_send_scan_done(wiphy_to_dev(request->wiphy), dev);
+                nl80211_send_scan_done(rdev, dev);
 
 #ifdef CONFIG_WIRELESS_EXT
         if (!request->aborted) {
@@ -57,11 +52,22 @@ void __cfg80211_scan_done(struct work_struct *wk)
 
         dev_put(dev);
 
-        cfg80211_unlock_rdev(rdev);
-        wiphy_to_dev(request->wiphy)->scan_req = NULL;
+        rdev->scan_req = NULL;
         kfree(request);
 }
 
+void __cfg80211_scan_done(struct work_struct *wk)
+{
+        struct cfg80211_registered_device *rdev;
+
+        rdev = container_of(wk, struct cfg80211_registered_device,
+                            scan_done_wk);
+
+        cfg80211_lock_rdev(rdev);
+        ___cfg80211_scan_done(rdev);
+        cfg80211_unlock_rdev(rdev);
+}
+
 void cfg80211_scan_done(struct cfg80211_scan_request *request, bool aborted)
 {
         WARN_ON(request != wiphy_to_dev(request->wiphy)->scan_req);