cfg80211: fix BSS struct IE access races

When a BSS struct is updated, the IEs are currently
overwritten or freed. This can lead to races if some
other CPU is accessing the BSS struct and using the
IEs concurrently.

Fix this by always allocating the IEs in a new struct
that holds the data and length and protecting access
to this new struct with RCU.

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

1 files changed, 27 insertions, 14 deletions

diff --git a/include/net/cfg80211.h b/include/net/cfg80211.h
index 731b48fa238b..8e6a6b73b9c9 100644
--- a/include/net/cfg80211.h
+++ b/include/net/cfg80211.h
@@ -1206,6 +1206,18 @@ enum cfg80211_signal_type {
 };
 
 /**
+ * struct cfg80211_bss_ie_data - BSS entry IE data
+ * @rcu_head: internal use, for freeing
+ * @len: length of the IEs
+ * @data: IE data
+ */
+struct cfg80211_bss_ies {
+	struct rcu_head rcu_head;
+	int len;
+	u8 data[];
+};
+
+/**
  * struct cfg80211_bss - BSS description
  *
  * This structure describes a BSS (which may also be a mesh network)
@@ -1216,36 +1228,34 @@ enum cfg80211_signal_type {
  * @tsf: timestamp of last received update
  * @beacon_interval: the beacon interval as from the frame
  * @capability: the capability field in host byte order
- * @information_elements: the information elements (Note that there
+ * @ies: the information elements (Note that there
  *	is no guarantee that these are well-formed!); this is a pointer to
  *	either the beacon_ies or proberesp_ies depending on whether Probe
  *	Response frame has been received
- * @len_information_elements: total length of the information elements
  * @beacon_ies: the information elements from the last Beacon frame
- * @len_beacon_ies: total length of the beacon_ies
  * @proberesp_ies: the information elements from the last Probe Response frame
- * @len_proberesp_ies: total length of the proberesp_ies
  * @signal: signal strength value (type depends on the wiphy's signal_type)
  * @free_priv: function pointer to free private data
  * @priv: private area for driver use, has at least wiphy->bss_priv_size bytes
  */
 struct cfg80211_bss {
+	u64 tsf;
+
 	struct ieee80211_channel *channel;
 
-	u8 bssid[ETH_ALEN];
-	u64 tsf;
+	const struct cfg80211_bss_ies __rcu *ies;
+	const struct cfg80211_bss_ies __rcu *beacon_ies;
+	const struct cfg80211_bss_ies __rcu *proberesp_ies;
+
+	void (*free_priv)(struct cfg80211_bss *bss);
+
+	s32 signal;
+
 	u16 beacon_interval;
 	u16 capability;
-	u8 *information_elements;
-	size_t len_information_elements;
-	u8 *beacon_ies;
-	size_t len_beacon_ies;
-	u8 *proberesp_ies;
-	size_t len_proberesp_ies;
 
-	s32 signal;
+	u8 bssid[ETH_ALEN];
 
-	void (*free_priv)(struct cfg80211_bss *bss);
 	u8 priv[0] __attribute__((__aligned__(sizeof(void *))));
 };
 
@@ -1253,6 +1263,9 @@ struct cfg80211_bss {
  * ieee80211_bss_get_ie - find IE with given ID
  * @bss: the bss to search
  * @ie: the IE ID
+ *
+ * Note that the return value is an RCU-protected pointer, so
+ * rcu_read_lock() must be held when calling this function.
  * Returns %NULL if not found.
  */
 const u8 *ieee80211_bss_get_ie(struct cfg80211_bss *bss, u8 ie);