Author: adrian
Date: Mon Sep  7 23:16:39 2015
New Revision: 287543
URL: https://svnweb.freebsd.org/changeset/base/287543

Log:
  Don't call enable_all_rings if the adapter has been freed.
  
  This is a subtle use-after-free race that results in some very undesirable
  hang behaviour.
  
  Reviewed by:  pkelsey
  Obtained from:        Kip Macy, NextBSD 
(https://github.com/NextBSD/NextBSD/commit/91a9bd1dbb33dafb41684d054e59d73976de9654)

Modified:
  head/sys/dev/netmap/netmap.c

Modified: head/sys/dev/netmap/netmap.c
==============================================================================
--- head/sys/dev/netmap/netmap.c        Mon Sep  7 21:59:11 2015        
(r287542)
+++ head/sys/dev/netmap/netmap.c        Mon Sep  7 23:16:39 2015        
(r287543)
@@ -2841,10 +2841,12 @@ void
 netmap_detach(struct ifnet *ifp)
 {
        struct netmap_adapter *na = NA(ifp);
+       int skip;
 
        if (!na)
                return;
 
+       skip = 0;
        NMG_LOCK();
        netmap_disable_all_rings(ifp);
        na->ifp = NULL;
@@ -2856,10 +2858,11 @@ netmap_detach(struct ifnet *ifp)
         * the driver is gone.
         */
        if (na->na_flags & NAF_NATIVE) {
-               netmap_adapter_put(na);
+               skip = netmap_adapter_put(na);
        }
        /* give them a chance to notice */
-       netmap_enable_all_rings(ifp);
+       if (skip == 0)
+               netmap_enable_all_rings(ifp);
        NMG_UNLOCK();
 }
 
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