cfg80211: validate SSID/MBSSID element ordering assumption

BugLink: https://bugs.launchpad.net/bugs/1848039
commit 242b0931c1918c56cd1dc5563fd250a3c39b996d upstream.

The code copying the data assumes that the SSID element is
before the MBSSID element, but since the data is untrusted
from the AP, this cannot be guaranteed.

Validate that this is indeed the case and ignore the MBSSID
otherwise, to avoid having to deal with both cases for the
copy of data that should be between them.

Cc: stable@vger.kernel.org
Fixes: 0b8fb8235be8 ("cfg80211: Parsing of Multiple BSSID information in scanning")
Link: https://lore.kernel.org/r/1569009255-I1673911f5eae02964e21bdc11b2bf58e5e207e59@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/wireless/scan.c b/net/wireless/scan.c
index d66e6d4b75555e991699fbd0cd4dbd7e5159942a..27d76c4c5cea1ac016afbefc103753057546e24d 100644 (file)
--- a/net/wireless/scan.c
+++ b/net/wireless/scan.c
@@ -1711,7 +1711,12 @@ cfg80211_update_notlisted_nontrans(struct wiphy *wiphy,
                return;
        new_ie_len -= trans_ssid[1];
        mbssid = cfg80211_find_ie(WLAN_EID_MULTIPLE_BSSID, ie, ielen);
-       if (!mbssid)
+       /*
+        * It's not valid to have the MBSSID element before SSID
+        * ignore if that happens - the code below assumes it is
+        * after (while copying things inbetween).
+        */
+       if (!mbssid || mbssid < trans_ssid)
                return;
        new_ie_len -= mbssid[1];
        rcu_read_lock();