mac80211: set bss_info data before configuring the channel

When mac80211 changes the channel, it also calls into the driver's
bss_info_changed() callback, e.g. with BSS_CHANGED_IDLE. The driver
may, like iwlwifi does, access more data from bss_info in that case
and iwlwifi accesses the basic_rates bitmap, but if changing from a
band with more (basic) rates to one with fewer, an out-of-bounds
access of the rate array may result.

While we can't avoid having invalid data at some point in time, we
can avoid having it while we call the driver - so set up all the
data before configuring the channel, and then apply it afterwards.

This fixes https://bugzilla.kernel.org/show_bug.cgi?id=195677

Reported-by: Johannes Hirte <johannes.hirte@datenkhaos.de>
Tested-by: Johannes Hirte <johannes.hirte@datenkhaos.de>
Debugged-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 28 insertions, 10 deletions

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 2f46db7d3afc..cc8e6ea1b27e 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -4392,15 +4392,19 @@ static int ieee80211_prep_connection(struct ieee80211_sub_if_data *sdata,
                         return -ENOMEM;
         }
 
-        if (new_sta || override) {
-                err = ieee80211_prep_channel(sdata, cbss);
-                if (err) {
-                        if (new_sta)
-                                sta_info_free(local, new_sta);
-                        return -EINVAL;
-                }
-        }
-
+        /*
+         * Set up the information for the new channel before setting the
+         * new channel. We can't - completely race-free - change the basic
+         * rates bitmap and the channel (sband) that it refers to, but if
+         * we set it up before we at least avoid calling into the driver's
+         * bss_info_changed() method with invalid information (since we do
+         * call that from changing the channel - only for IDLE and perhaps
+         * some others, but ...).
+         *
+         * So to avoid that, just set up all the new information before the
+         * channel, but tell the driver to apply it only afterwards, since
+         * it might need the new channel for that.
+         */
         if (new_sta) {
                 u32 rates = 0, basic_rates = 0;
                 bool have_higher_than_11mbit;
@@ -4471,8 +4475,22 @@ static int ieee80211_prep_connection(struct ieee80211_sub_if_data *sdata,
                         sdata->vif.bss_conf.sync_dtim_count = 0;
                 }
                 rcu_read_unlock();
+        }
 
-                /* tell driver about BSSID, basic rates and timing */
+        if (new_sta || override) {
+                err = ieee80211_prep_channel(sdata, cbss);
+                if (err) {
+                        if (new_sta)
+                                sta_info_free(local, new_sta);
+                        return -EINVAL;
+                }
+        }
+
+        if (new_sta) {
+                /*
+                 * tell driver about BSSID, basic rates and timing
+                 * this was set up above, before setting the channel
+                 */
                 ieee80211_bss_info_change_notify(sdata,
                         BSS_CHANGED_BSSID | BSS_CHANGED_BASIC_RATES |
                         BSS_CHANGED_BEACON_INT);