mac80211: fix rx monitor filter refcounters

This patch fixes an refcounting bug. Previously it
was possible to corrupt the per-device recv. filter
and monitor management counters when:
	iw dev wlanX set monitor [new flags]
was issued on an active monitor interface.

Acked-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 30 insertions, 2 deletions

diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index c981604b71e..9e63fc28f85 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -68,8 +68,36 @@ static int ieee80211_change_iface(struct wiphy *wiphy,
                  params && params->use_4addr >= 0)
                 sdata->u.mgd.use_4addr = params->use_4addr;
 
-        if (sdata->vif.type == NL80211_IFTYPE_MONITOR && flags)
-                sdata->u.mntr_flags = *flags;
+        if (sdata->vif.type == NL80211_IFTYPE_MONITOR && flags) {
+                struct ieee80211_local *local = sdata->local;
+
+                if (ieee80211_sdata_running(sdata)) {
+                        /*
+                         * Prohibit MONITOR_FLAG_COOK_FRAMES to be
+                         * changed while the interface is up.
+                         * Else we would need to add a lot of cruft
+                         * to update everything:
+                         *      cooked_mntrs, monitor and all fif_* counters
+                         *      reconfigure hardware
+                         */
+                        if ((*flags & MONITOR_FLAG_COOK_FRAMES) !=
+                            (sdata->u.mntr_flags & MONITOR_FLAG_COOK_FRAMES))
+                                return -EBUSY;
+
+                        ieee80211_adjust_monitor_flags(sdata, -1);
+                        sdata->u.mntr_flags = *flags;
+                        ieee80211_adjust_monitor_flags(sdata, 1);
+
+                        ieee80211_configure_filter(local);
+                } else {
+                        /*
+                         * Because the interface is down, ieee80211_do_stop
+                         * and ieee80211_do_open take care of "everything"
+                         * mentioned in the comment above.
+                         */
+                        sdata->u.mntr_flags = *flags;
+                }
+        }
 
         return 0;
 }