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, 18 insertions, 9 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 4a719770eaaf..f45706adaf34 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -4808,6 +4808,7 @@ static int nl80211_send_bss(struct sk_buff *msg, struct netlink_callback *cb,
                             struct cfg80211_internal_bss *intbss)
 {
         struct cfg80211_bss *res = &intbss->pub;
+        const struct cfg80211_bss_ies *ies;
         void *hdr;
         struct nlattr *bss;
 
@@ -4828,16 +4829,24 @@ static int nl80211_send_bss(struct sk_buff *msg, struct netlink_callback *cb,
         if (!bss)
                 goto nla_put_failure;
         if ((!is_zero_ether_addr(res->bssid) &&
-             nla_put(msg, NL80211_BSS_BSSID, ETH_ALEN, res->bssid)) ||
-            (res->information_elements && res->len_information_elements &&
-             nla_put(msg, NL80211_BSS_INFORMATION_ELEMENTS,
-                     res->len_information_elements,
-                     res->information_elements)) ||
-            (res->beacon_ies && res->len_beacon_ies &&
-             res->beacon_ies != res->information_elements &&
-             nla_put(msg, NL80211_BSS_BEACON_IES,
-                     res->len_beacon_ies, res->beacon_ies)))
+             nla_put(msg, NL80211_BSS_BSSID, ETH_ALEN, res->bssid)))
                 goto nla_put_failure;
+
+        rcu_read_lock();
+        ies = rcu_dereference(res->ies);
+        if (ies && ies->len && nla_put(msg, NL80211_BSS_INFORMATION_ELEMENTS,
+                                       ies->len, ies->data)) {
+                rcu_read_unlock();
+                goto nla_put_failure;
+        }
+        ies = rcu_dereference(res->beacon_ies);
+        if (ies && ies->len && nla_put(msg, NL80211_BSS_BEACON_IES,
+                                       ies->len, ies->data)) {
+                rcu_read_unlock();
+                goto nla_put_failure;
+        }
+        rcu_read_unlock();
+
         if (res->tsf &&
             nla_put_u64(msg, NL80211_BSS_TSF, res->tsf))
                 goto nla_put_failure;