mac80211: fix a race condition in the cfg80211 scanning code (thx, johill)

SVN-Revision: 17341

package/mac80211/patches/100-cfg80211_fix_scan_check_again.patch

@@ -0,0 +1,98 @@
+Subject: cfg80211: check lost scans later, fix bug
+
+When we lose a scan, cfg80211 tries to clean up after
+the driver. However, it currently does this too early,
+it does this in GOING_DOWN already instead of DOWN, so
+it may happen with mac80211. Besides fixing this, also
+make it more robust by leaking the scan request so if
+the driver later actually finishes the scan, it won't
+crash. Also check in ___cfg80211_scan_done whether a
+scan request is still pending and exit if not.
+
+Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
+---
+ net/wireless/core.c |    4 +++-
+ net/wireless/core.h |    2 +-
+ net/wireless/scan.c |   19 ++++++++++++++++---
+ 3 files changed, 20 insertions(+), 5 deletions(-)
+
+--- a/net/wireless/core.c
++++ b/net/wireless/core.c
+@@ -664,7 +664,7 @@ static void wdev_cleanup_work(struct wor
+ 
+ 	if (WARN_ON(rdev->scan_req && rdev->scan_req->dev == wdev->netdev)) {
+ 		rdev->scan_req->aborted = true;
+-		___cfg80211_scan_done(rdev);
++		___cfg80211_scan_done(rdev, true);
+ 	}
+ 
+ 	cfg80211_unlock_rdev(rdev);
+@@ -755,6 +755,8 @@ static int cfg80211_netdev_notifier_call
+ 		default:
+ 			break;
+ 		}
++		break;
++	case NETDEV_DOWN:
+ 		dev_hold(dev);
+ 		schedule_work(&wdev->cleanup_work);
+ 		break;
+--- a/net/wireless/core.h
++++ b/net/wireless/core.h
+@@ -374,7 +374,7 @@ void cfg80211_sme_scan_done(struct net_d
+ 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_scan_done(struct cfg80211_registered_device *rdev, bool leak);
+ void cfg80211_upload_connect_keys(struct wireless_dev *wdev);
+ 
+ struct ieee80211_channel *
+--- a/net/wireless/scan.c
++++ b/net/wireless/scan.c
+@@ -18,7 +18,7 @@
+ 
+ #define IEEE80211_SCAN_RESULT_EXPIRE	(15 * HZ)
+ 
+-void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev)
++void ___cfg80211_scan_done(struct cfg80211_registered_device *rdev, bool leak)
+ {
+ 	struct cfg80211_scan_request *request;
+ 	struct net_device *dev;
+@@ -28,6 +28,9 @@ void ___cfg80211_scan_done(struct cfg802
+ 
+ 	request = rdev->scan_req;
+ 
++	if (!request)
++		return;
++
+ 	dev = request->dev;
+ 
+ 	/*
+@@ -53,7 +56,17 @@ void ___cfg80211_scan_done(struct cfg802
+ 	dev_put(dev);
+ 
+ 	rdev->scan_req = NULL;
+-	kfree(request);
++
++	/*
++	 * OK. If this is invoked with "leak" then we can't
++	 * free this ... but we've cleaned it up anyway. The
++	 * driver failed to call the scan_done callback, so
++	 * all bets are off, it might still be trying to use
++	 * the scan request or not ... if it accesses the dev
++	 * in there (it shouldn't anyway) then it may crash.
++	 */
++	if (!leak)
++		kfree(request);
+ }
+ 
+ void __cfg80211_scan_done(struct work_struct *wk)
+@@ -64,7 +77,7 @@ void __cfg80211_scan_done(struct work_st
+ 			    scan_done_wk);
+ 
+ 	cfg80211_lock_rdev(rdev);
+-	___cfg80211_scan_done(rdev);
++	___cfg80211_scan_done(rdev, false);
+ 	cfg80211_unlock_rdev(rdev);
+ }
+