wifi: mac80211: Fix UAF in ieee80211_scan_rx()

ieee80211_scan_rx() tries to access scan_req->flags after a
null check, but a UAF is observed when the scan is completed
and __ieee80211_scan_completed() executes, which then calls
cfg80211_scan_done() leading to the freeing of scan_req.

Since scan_req is rcu_dereference()'d, prevent the racing in
__ieee80211_scan_completed() by ensuring that from mac80211's
POV it is no longer accessed from an RCU read critical section
before we call cfg80211_scan_done().

Cc: stable@vger.kernel.org
Link: https://syzkaller.appspot.com/bug?extid=f9acff9bf08a845f225d
Reported-by: syzbot+f9acff9bf08a845f225d@syzkaller.appspotmail.com
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
Link: https://lore.kernel.org/r/20220819200340.34826-1-code@siddh.me
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index fa8ddf576bc1c88e31984e1fc8d746813b3f9b09..c4f2aeb31da3ad2b8428b7e36ce36bd9d434c1d5 100644 (file)
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -469,16 +469,19 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
        scan_req = rcu_dereference_protected(local->scan_req,
                                             lockdep_is_held(&local->mtx));
 
-       if (scan_req != local->int_scan_req) {
-               local->scan_info.aborted = aborted;
-               cfg80211_scan_done(scan_req, &local->scan_info);
-       }
        RCU_INIT_POINTER(local->scan_req, NULL);
        RCU_INIT_POINTER(local->scan_sdata, NULL);
 
        local->scanning = 0;
        local->scan_chandef.chan = NULL;
 
+       synchronize_rcu();
+
+       if (scan_req != local->int_scan_req) {
+               local->scan_info.aborted = aborted;
+               cfg80211_scan_done(scan_req, &local->scan_info);
+       }
+
        /* Set power back to normal operating levels. */
        ieee80211_hw_config(local, 0);