cfg80211: fix locking in nl80211_set_wiphy

Luis reports that there's a circular locking dependency;
this is because cfg80211_dev_rename() will acquire the
cfg80211_mutex while the device mutex is held, while
this normally is done the other way around. The solution
is to open-code the device-getting in nl80211_set_wiphy
and require holding the mutex around cfg80211_dev_rename
rather than acquiring it within.

Also fix a bug -- rtnl locking is expected by drivers so
we need to provide it.

Reported-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 20 insertions, 8 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 8808431..353e1a4 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -366,16 +366,26 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 	int result = 0, rem_txq_params = 0;
 	struct nlattr *nl_txq_params;
 
-	rdev = cfg80211_get_dev_from_info(info);
-	if (IS_ERR(rdev))
-		return PTR_ERR(rdev);
+	rtnl_lock();
+
+	mutex_lock(&cfg80211_mutex);
+
+	rdev = __cfg80211_drv_from_info(info);
+	if (IS_ERR(rdev)) {
+		result = PTR_ERR(rdev);
+		goto unlock;
+	}
 
-	if (info->attrs[NL80211_ATTR_WIPHY_NAME]) {
+	mutex_lock(&rdev->mtx);
+
+	if (info->attrs[NL80211_ATTR_WIPHY_NAME])
 		result = cfg80211_dev_rename(
 			rdev, nla_data(info->attrs[NL80211_ATTR_WIPHY_NAME]));
-		if (result)
-			goto bad_res;
-	}
+
+	mutex_unlock(&cfg80211_mutex);
+
+	if (result)
+		goto bad_res;
 
 	if (info->attrs[NL80211_ATTR_WIPHY_TXQ_PARAMS]) {
 		struct ieee80211_txq_params txq_params;
@@ -471,7 +481,9 @@ static int nl80211_set_wiphy(struct sk_buff *skb, struct genl_info *info)
 
 
  bad_res:
-	cfg80211_put_dev(rdev);
+	mutex_unlock(&rdev->mtx);
+ unlock:
+	rtnl_unlock();
 	return result;
 }