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 8808431bd581..353e1a4ece83 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;
 }