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>

3 files changed, 33 insertions, 28 deletions

diff --git a/net/wireless/core.c b/net/wireless/core.c
index 17fe39049740..d1f556535f6d 100644
--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -87,7 +87,7 @@ struct wiphy *wiphy_idx_to_wiphy(int wiphy_idx)
 }
 
 /* requires cfg80211_mutex to be held! */
-static struct cfg80211_registered_device *
+struct cfg80211_registered_device *
 __cfg80211_drv_from_info(struct genl_info *info)
 {
         int ifindex;
@@ -176,13 +176,14 @@ void cfg80211_put_dev(struct cfg80211_registered_device *drv)
         mutex_unlock(&drv->mtx);
 }
 
+/* requires cfg80211_mutex to be held */
 int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
                         char *newname)
 {
         struct cfg80211_registered_device *drv;
         int wiphy_idx, taken = -1, result, digits;
 
-        mutex_lock(&cfg80211_mutex);
+        assert_cfg80211_lock();
 
         /* prohibit calling the thing phy%d when %d is not its number */
         sscanf(newname, PHY_NAME "%d%n", &wiphy_idx, &taken);
@@ -195,30 +196,23 @@ int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
                  * deny the name if it is phy<idx> where <idx> is printed
                  * without leading zeroes. taken == strlen(newname) here
                  */
-                result = -EINVAL;
                 if (taken == strlen(PHY_NAME) + digits)
-                        goto out_unlock;
+                        return -EINVAL;
         }
 
 
         /* Ignore nop renames */
-        result = 0;
         if (strcmp(newname, dev_name(&rdev->wiphy.dev)) == 0)
-                goto out_unlock;
+                return 0;
 
         /* Ensure another device does not already have this name. */
-        list_for_each_entry(drv, &cfg80211_drv_list, list) {
-                result = -EINVAL;
+        list_for_each_entry(drv, &cfg80211_drv_list, list)
                 if (strcmp(newname, dev_name(&drv->wiphy.dev)) == 0)
-                        goto out_unlock;
-        }
+                        return -EINVAL;
 
-        /* this will only check for collisions in sysfs
-         * which is not even always compiled in.
-         */
         result = device_rename(&rdev->wiphy.dev, newname);
         if (result)
-                goto out_unlock;
+                return result;
 
         if (rdev->wiphy.debugfsdir &&
             !debugfs_rename(rdev->wiphy.debugfsdir->d_parent,
@@ -228,13 +222,9 @@ int cfg80211_dev_rename(struct cfg80211_registered_device *rdev,
                 printk(KERN_ERR "cfg80211: failed to rename debugfs dir to %s!\n",
                        newname);
 
-        result = 0;
-out_unlock:
-        mutex_unlock(&cfg80211_mutex);
-        if (result == 0)
-                nl80211_notify_dev_rename(rdev);
+        nl80211_notify_dev_rename(rdev);
 
-        return result;
+        return 0;
 }
 
 /* exported functions */
diff --git a/net/wireless/core.h b/net/wireless/core.h
index 97a6fd8b2b03..d43daa236ef9 100644
--- a/net/wireless/core.h
+++ b/net/wireless/core.h
@@ -99,6 +99,9 @@ struct cfg80211_internal_bss {
 struct cfg80211_registered_device *cfg80211_drv_by_wiphy_idx(int wiphy_idx);
 int get_wiphy_idx(struct wiphy *wiphy);
 
+struct cfg80211_registered_device *
+__cfg80211_drv_from_info(struct genl_info *info);
+
 /*
  * This function returns a pointer to the driver
  * that the genl_info item that is passed refers to.
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;
 }