mac80211: fix deadlock with multiple interfaces

The locking around ieee80211_recalc_smps is
buggy -- it cannot acquire another interface's
mutex while the iflist mutex is held because
another code path could be holding the iface
mutex and trying to acquire the iflist mutex.

But the locking is also unnecessary, we only
check "ifmgd->associated" as a bool, and don't
use the pointer (in check_mgd_smps).

Reported-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 3 insertions, 17 deletions

diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index aba025d748e9..4ee8f2b53cb7 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1297,16 +1297,12 @@ static int check_mgd_smps(struct ieee80211_if_managed *ifmgd,
 }
 
 /* must hold iflist_mtx */
-void ieee80211_recalc_smps(struct ieee80211_local *local,
-			   struct ieee80211_sub_if_data *forsdata)
+void ieee80211_recalc_smps(struct ieee80211_local *local)
 {
 	struct ieee80211_sub_if_data *sdata;
 	enum ieee80211_smps_mode smps_mode = IEEE80211_SMPS_OFF;
 	int count = 0;
 
-	if (forsdata)
-		lockdep_assert_held(&forsdata->u.mgd.mtx);
-
 	lockdep_assert_held(&local->iflist_mtx);
 
 	/*
@@ -1324,18 +1320,8 @@ void ieee80211_recalc_smps(struct ieee80211_local *local,
 			continue;
 		if (sdata->vif.type != NL80211_IFTYPE_STATION)
 			goto set;
-		if (sdata != forsdata) {
-			/*
-			 * This nested is ok -- we are holding the iflist_mtx
-			 * so can't get here twice or so. But it's required
-			 * since normally we acquire it first and then the
-			 * iflist_mtx.
-			 */
-			mutex_lock_nested(&sdata->u.mgd.mtx, SINGLE_DEPTH_NESTING);
-			count += check_mgd_smps(&sdata->u.mgd, &smps_mode);
-			mutex_unlock(&sdata->u.mgd.mtx);
-		} else
-			count += check_mgd_smps(&sdata->u.mgd, &smps_mode);
+
+		count += check_mgd_smps(&sdata->u.mgd, &smps_mode);
 
 		if (count > 1) {
 			smps_mode = IEEE80211_SMPS_OFF;