cfg80211: comprehensively check station changes

The station change API isn't being checked properly before
drivers are called, and as a result it is difficult to see
what should be allowed and what not.

In order to comprehensively check the API parameters parse
everything first, and then have the driver call a function
(cfg80211_check_station_change()) with the additionally
information about the kind of station that is being changed;
this allows the function to make better decisions than the
old code could.

While at it, also add a few checks, particularly in mesh
and clarify the TDLS station lifetime in documentation.

To be able to reduce a few checks, ignore any flag set bits
when the mask isn't set, they shouldn't be applied then.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

2 files changed, 60 insertions, 4 deletions

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 7ca321d2b599..ed2b08da3b93 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -678,6 +678,49 @@ struct station_parameters {
 };
 
 /**
+ * enum cfg80211_station_type - the type of station being modified
+ * @CFG80211_STA_AP_CLIENT: client of an AP interface
+ * @CFG80211_STA_AP_MLME_CLIENT: client of an AP interface that has
+ *      the AP MLME in the device
+ * @CFG80211_STA_AP_STA: AP station on managed interface
+ * @CFG80211_STA_IBSS: IBSS station
+ * @CFG80211_STA_TDLS_PEER_SETUP: TDLS peer on managed interface (dummy entry
+ *      while TDLS setup is in progress, it moves out of this state when
+ *      being marked authorized; use this only if TDLS with external setup is
+ *      supported/used)
+ * @CFG80211_STA_TDLS_PEER_ACTIVE: TDLS peer on managed interface (active
+ *      entry that is operating, has been marked authorized by userspace)
+ * @CFG80211_STA_MESH_PEER_NONSEC: peer on mesh interface (non-secured)
+ * @CFG80211_STA_MESH_PEER_SECURE: peer on mesh interface (secured)
+ */
+enum cfg80211_station_type {
+        CFG80211_STA_AP_CLIENT,
+        CFG80211_STA_AP_MLME_CLIENT,
+        CFG80211_STA_AP_STA,
+        CFG80211_STA_IBSS,
+        CFG80211_STA_TDLS_PEER_SETUP,
+        CFG80211_STA_TDLS_PEER_ACTIVE,
+        CFG80211_STA_MESH_PEER_NONSEC,
+        CFG80211_STA_MESH_PEER_SECURE,
+};
+
+/**
+ * cfg80211_check_station_change - validate parameter changes
+ * @wiphy: the wiphy this operates on
+ * @params: the new parameters for a station
+ * @statype: the type of station being modified
+ *
+ * Utility function for the @change_station driver method. Call this function
+ * with the appropriate station type looking up the station (and checking that
+ * it exists). It will verify whether the station change is acceptable, and if
+ * not will return an error code. Note that it may modify the parameters for
+ * backward compatibility reasons, so don't use them before calling this.
+ */
+int cfg80211_check_station_change(struct wiphy *wiphy,
+                                  struct station_parameters *params,
+                                  enum cfg80211_station_type statype);
+
+/**
  * enum station_info_flags - station information flags
  *
  * Used by the driver to indicate which info in &struct station_info
@@ -1770,9 +1813,8 @@ struct cfg80211_gtk_rekey_data {
  * @change_station: Modify a given station. Note that flags changes are not much
  *      validated in cfg80211, in particular the auth/assoc/authorized flags
  *      might come to the driver in invalid combinations -- make sure to check
- *      them, also against the existing state! Also, supported_rates changes are
- *      not checked in station mode -- drivers need to reject (or ignore) them
- *      for anything but TDLS peers.
+ *      them, also against the existing state! Drivers must call
+ *      cfg80211_check_station_change() to validate the information.
  * @get_station: get station information for the station identified by @mac
  * @dump_station: dump station callback -- resume dump at index @idx
  *
diff --git a/include/uapi/linux/nl80211.h b/include/uapi/linux/nl80211.h
index 7dcc69f73d2c..523ed3d65b41 100644
--- a/include/uapi/linux/nl80211.h
+++ b/include/uapi/linux/nl80211.h
@@ -36,7 +36,21 @@
  * The station is still assumed to belong to the AP interface it was added
  * to.
  *
- * TODO: need more info?
+ * Station handling varies per interface type and depending on the driver's
+ * capabilities.
+ *
+ * For drivers supporting TDLS with external setup (WIPHY_FLAG_SUPPORTS_TDLS
+ * and WIPHY_FLAG_TDLS_EXTERNAL_SETUP), the station lifetime is as follows:
+ *  - a setup station entry is added, not yet authorized, without any rate
+ *    or capability information, this just exists to avoid race conditions
+ *  - when the TDLS setup is done, a single NL80211_CMD_SET_STATION is valid
+ *    to add rate and capability information to the station and at the same
+ *    time mark it authorized.
+ *  - %NL80211_TDLS_ENABLE_LINK is then used
+ *  - after this, the only valid operation is to remove it by tearing down
+ *    the TDLS link (%NL80211_TDLS_DISABLE_LINK)
+ *
+ * TODO: need more info for other interface types
  */
 
 /**