nl/cfg80211: force scan using an AP vif if requested

If the user wants to scan using a vif configured as AP,
cfg80211 must give him a chance to do it, even if this
will disrupt the stations performance due to off-channel
scanning. To do so, this patch adds a 'force' flag to the
SCAN_TRIGGER command which tells cfg80211 to perform the
scanning operation even if the vif is an AP and the
beaconing has already started.

Signed-off-by: Antonio Quartulli <ordex@autistici.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

3 files changed, 21 insertions, 2 deletions

diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index 0e6277a06c29..617d0fbfc96f 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -3050,6 +3050,7 @@ enum nl80211_ap_sme_features {
  *      mode
  * @NL80211_FEATURE_LOW_PRIORITY_SCAN: This driver supports low priority scan
  * @NL80211_FEATURE_SCAN_FLUSH: Scan flush is supported
+ * @NL80211_FEATURE_AP_SCAN: Support scanning using an AP vif
  */
 enum nl80211_feature_flags {
         NL80211_FEATURE_SK_TX_STATUS                    = 1 << 0,
@@ -3060,6 +3061,7 @@ enum nl80211_feature_flags {
         NL80211_FEATURE_SAE                             = 1 << 5,
         NL80211_FEATURE_LOW_PRIORITY_SCAN               = 1 << 6,
         NL80211_FEATURE_SCAN_FLUSH                      = 1 << 7,
+        NL80211_FEATURE_AP_SCAN                         = 1 << 8,
 };
 
 /**
@@ -3103,10 +3105,16 @@ enum nl80211_connect_failed_reason {
  *
  * @NL80211_SCAN_FLAG_LOW_PRIORITY: scan request has low priority
  * @NL80211_SCAN_FLAG_FLUSH: flush cache before scanning
+ * @NL80211_SCAN_FLAG_AP: force a scan even if the interface is configured
+ *      as AP and the beaconing has already been configured. This attribute is
+ *      dangerous because will destroy stations performance as a lot of frames
+ *      will be lost while scanning off-channel, therefore it must be used only
+ *      when really needed
  */
 enum nl80211_scan_flags {
         NL80211_SCAN_FLAG_LOW_PRIORITY                  = 1<<0,
         NL80211_SCAN_FLAG_FLUSH                         = 1<<1,
+        NL80211_SCAN_FLAG_AP                            = 1<<2,
 };
 
 #endif /* __LINUX_NL80211_H */
diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c
index 5739bfbf2999..5eab1325a0f6 100644
--- a/net/mac80211/cfg.c
+++ b/net/mac80211/cfg.c
@@ -1855,7 +1855,16 @@ static int ieee80211_scan(struct wiphy *wiphy,
                  * beaconing hasn't been configured yet
                  */
         case NL80211_IFTYPE_AP:
-                if (sdata->u.ap.beacon)
+                /*
+                 * If the scan has been forced (and the driver supports
+                 * forcing), don't care about being beaconing already.
+                 * This will create problems to the attached stations (e.g. all
+                 * the  frames sent while scanning on other channel will be
+                 * lost)
+                 */
+                if (sdata->u.ap.beacon &&
+                    (!(wiphy->features & NL80211_FEATURE_AP_SCAN) ||
+                     !(req->flags & NL80211_SCAN_FLAG_AP)))
                         return -EOPNOTSUPP;
                 break;
         default:
diff --git a/net/mac80211/main.c b/net/mac80211/main.c
index ba5a23249771..c42094be2f0b 100644
--- a/net/mac80211/main.c
+++ b/net/mac80211/main.c
@@ -603,7 +603,9 @@ struct ieee80211_hw *ieee80211_alloc_hw(size_t priv_data_len,
                            NL80211_FEATURE_HT_IBSS;
 
         if (!ops->hw_scan)
-                wiphy->features |= NL80211_FEATURE_LOW_PRIORITY_SCAN;
+                wiphy->features |= NL80211_FEATURE_LOW_PRIORITY_SCAN |
+                                   NL80211_FEATURE_AP_SCAN;
+
 
         if (!ops->set_key)
                 wiphy->flags |= WIPHY_FLAG_IBSS_RSN;